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  • 1.
    Abdulrazaq, Muhammed
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Extensional Instability in Complex Fluids: A Computational Study2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this study, instability and failure in complex fluids (Elastoviscoplastic fluids) is explored using the classic Considère (F˙ < 0) and stress curvature (σ¨ < 0) criteria. Employing the Saramito model, numerical simulation of the extensional protocol on non-Newtonian fluids is carried out. Validation is firstly performed (with a purely viscoelastic model) and in general found to be in agreement with previous works. Parameter variation of the Bingham number (Bi), capillary number (Ca) and extension rate (ε˙) is then undertaken. It is found out that for Oldroyd-B based fluids, the stress curvature condition almost always occurs from inception of the flow for all cases. Additionally, increasing surface tension has a stabilizing effect on the extending fluid when it is below a critical value, above which it aids breakup. Increasing the yield stress, though, delays the onset of instability, but reduces the final length of the extending filament. At mild to high extension rates, the Considère criterion and the extension at the maximum stress are suit-able indicators of the final extension at strain-to-break(εST B). Furthermore, the rate of the of necking instability till final breakup varies with the εST B at moderate to high ε˙.

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  • 2. Abdulrazaq, Muhammed
    et al.
    Shahmardi, Armin
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Edoardo Rost, Marco
    Brandt, Luca
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
    Numerical modelling of the extensional dynamics in elastoviscoplastic fluidsManuscript (preprint) (Other academic)
    Abstract [en]

    The extensional dynamics of an elasto-viscoplastic (EVP) fluid is studied by means of numerical simulations closely modelling an experimental configuration.  Specifically, we track the interface between the EVP material and the Newtonian medium using an algebraic volume of fluid method (MTHINC-VOF) and employ a fully Eulerian immersed boundary method (IBM) to model the motion of the piston responsible of the extension of the material.

    We investigate the role of different values of the yield stress, surface tension at the interface between the EVP material and the surrounding fluid, polymer viscosity ratio, and extension rates on the necking thickness of the material, extensional viscosity, and yielding of the material. 

     The results of the simulations reveal that when the yield stress of the EVP material is much larger than the viscous stresses, the material undergoes an elastic deformation, regardless of the selected values of extension rate, interfacial forces, and viscosity ratio. Moreover, increasing the ratio of the polymeric viscosity to the total viscosity of the system accelerates the EVP rupture due to the high stress concentration in the central part of the material sample. Specific and novel to our study, we show that interfacial forces cannot be ignored when the surface tension coefficient is such that a Capillary number based on the extensional rate is order 1. For large values of the surface tension coefficient, the EVP material fails sooner, with a clear deviation from the exponential reduction in the neck thickness.

  • 3. Abreu, L. I.
    et al.
    Cavalieri, A. V. G.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Reduced-order models to analyse coherent structures in turbulent pipe flow2019In: 11th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2019, International Symposium on Turbulence and Shear Flow Phenomena, TSFP , 2019Conference paper (Refereed)
    Abstract [en]

    Fully resolved direct numerical simulations, performed with a high-order spectral-element method, are used to study coherent structures in turbulent pipe flow at friction Reynolds numbers Reτ = 180 and 550 (El Khoury et al., 2013). The database was analysed using spectral proper orthogonal decomposition (SPOD) so as to identify dominant coherent structures, most of which are of streaky shape. As a reduced-order model for such structures, the linearised flow response to harmonic forcing was computed, and the analysed singular modes of the resolvent operator were analysed. For turbulent flows, this approach amounts to considering the non-linear terms in the Navier–Stokes system as an unknown forcing, treated convenienty as external. Resolvent analysis then allows an identification of the optimal forcing and most amplified flow response; the latter may be related to observed relevant structures obtained by SPOD, especially if the gain between forcing and response is much larger than what is found for suboptimal forcings or if the non-linear forcing is white noise. Results from SPOD and resolvent analysis were extracted for several combinations of frequencies, streamwise and azimuthal wavenumbers. For both Reynolds numbers, good agreement between SPOD and resolvent modes was observed for parameter combinations where the lift-up mechanism is present: optimal forcing from resolvent analysis represents streamwise vortices and the associated response are streaky structures.

  • 4. Abreu, Leandra, I
    et al.
    Cavalieri, Andre V. G.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Resolvent modelling of near-wall coherent structures in turbulent channel flow2020In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 85, article id 108662Article in journal (Refereed)
    Abstract [en]

    Turbulent channel flow was analysed using direct numerical simulations at friction Reynolds numbers Re-tau = 180 and 550. The databases were studied using spectral proper orthogonal decomposition (SPOD) to identify dominant near-wall coherent structures, most of which turn out to be streaks and streamwise vortices. Resolvent analysis was used as a theoretical approach to model such structures, as it allows the identification of the optimal forcing and most amplified flow response; the latter may be related to the observed relevant structures obtained by SPOD, especially if the gain between forcing and response is much larger than what is found for suboptimal forcings or if the non-linear forcing is white noise. Results from SPOD and resolvent analysis were compared for several combinations of frequencies and wavenumbers. For both Reynolds numbers, the best agreement between SPOD and resolvent modes was observed for the cases where the lift-up mechanism from resolvent analysis is present, which are also the cases where the optimal resolvent gain is dominant. These results confirm the outcomes in our previous studies (Abreu et al., 2019; Abreu et al., 2020), where we used a DNS database of a pipe flow for the same Reynolds numbers.

  • 5.
    Abreu, Leandra, I
    et al.
    Sao Paulo State Univ UNESP, Campus Sao Joao da Boa Vista, BR-13876750 Sao Joao da Boa Vista, SP, Brazil.;Inst Tecnol Aeronaut, Div Engn Aeronaut, BR-12228900 Sao Jose Dos Campos, SP, Brazil..
    Cavalieri, Andre V. G.
    Inst Tecnol Aeronaut, Div Engn Aeronaut, BR-12228900 Sao Jose Dos Campos, SP, Brazil..
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Stability, Transition and Control.
    Spectral proper orthogonal decomposition and resolvent analysis of near-wall coherent structures in turbulent pipe flows2020In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 900, article id A11Article in journal (Refereed)
    Abstract [en]

    Direct numerical simulations, performed with a high-order spectral-element method, are used to study coherent structures in turbulent pipe flow at friction Reynolds numbers Re-tau = 180 and 550. The database was analysed using spectral proper orthogonal decomposition (SPOD) to identify energetically dominant coherent structures, most of which turn out to be streaks and quasi-streamwise vortices. To understand how such structures can be modelled, the linear flow responses to harmonic forcing were computed using the singular value decomposition of the resolvent operator, using the mean field as a base flow. The SPOD and resolvent analysis were calculated for several combinations of frequencies and wavenumbers, allowing the mapping out of similarities between SPOD modes and optimal responses for a wide range of relevant scales in turbulent pipe flows. In order to explore physical reasons behind the agreement between both methods, an indicator of lift-up mechanism in the resolvent analysis was introduced, activated when optimal forcing is dominated by the wall-normal and azimuthal components, and associated response corresponds to streaks of streamwise velocity. Good agreement between leading SPOD and resolvent modes is observed in a large region of parameter space. In this region, a significant gain separation is found in resolvent analysis, which may be attributed to the strong amplification associated with the lift-up mechanism, here understood as nonlinear forcing terms leading to the appearance of streamwise vortices, which in turn form high-amplitude streaks. For both Reynolds numbers, the observed concordances were generally for structures with large energy in the buffer layer. The results highlight resolvent analysis as a pertinent reduced-order model for coherent structures in wall-bounded turbulence, particularly for streamwise elongated structures corresponding to near-wall streamwise vortices and streaks.

  • 6.
    Abreu, Leandra, I
    et al.
    Sao Paulo State Univ UNESP, Campus Sao Joao Boa Vista, BR-13876750 Sao Joao Da Boa Vista, SP, Brazil.;Inst Tecnol Aeronaut, Div Engn Aeronaut, BR-12228900 Sao Jose Dos Campos, SP, Brazil..
    Tanarro, Alvaro
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Cavalieri, Andre V. G.
    Inst Tecnol Aeronaut, Div Engn Aeronaut, BR-12228900 Sao Jose Dos Campos, SP, Brazil..
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Hanifi, Ardeshir
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Spanwise-coherent hydrodynamic waves around flat plates and airfoils2021In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 927, article id A1Article in journal (Refereed)
    Abstract [en]

    We investigate spanwise-coherent structures in the turbulent flow around airfoils, motivated by their connection with trailing-edge noise. We analyse well-resolved large-eddy simulations (LES) of the flow around NACA 0012 and NACA 4412 airfoils, both at a Reynolds number of 400 000 based on the chord length. Spectral proper orthogonal decomposition performed on the data reveals that the most energetic coherent structures are hydrodynamic waves, extending over the turbulent boundary layers around the airfoils with significant amplitudes near the trailing edge. Resolvent analysis was used to model such structures, using the mean field as a base flow. We then focus on evaluating the dependence of such structures on the domain size, to ensure that they are not an artefact of periodic boundary conditions in small computational boxes. To this end, we performed incompressible LES of a zero-pressure-gradient turbulent boundary layer, for three different spanwise sizes, with the momentum-thickness Reynolds number matching those near the airfoils trailing edge. The same coherent hydrodynamic waves were observed for the three domains. Such waves are accurately modelled as the most amplified flow response from resolvent analysis. The signature of such wide structures is seen in non-premultiplied spanwise wavenumber spectra, which collapse for the three computational domains. These results suggest that the spanwise-elongated structures are not domain-size dependent for the studied simulations, indicating thus the presence of very wide structures in wall-bounded turbulent flows.

  • 7.
    Abreu, Leandra I.
    et al.
    Divisão de Engenharia Aeronáutica, Instituto Tecnológico de Aeronáutica, 12228-900, São José dos Campos, SP, Brazil.
    Tanarro, Alvaro
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Cavalieri, André V.G.
    Divisão de Engenharia Aeronáutica, Instituto Tecnológico de Aeronáutica, 12228-900, São José dos Campos, SP, Brazil.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Superseded Departments (pre-2005), Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Hanifi, Ardeshir
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Superseded Departments (pre-2005), Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Wavepackets in turbulent flows around airfoilsManuscript (preprint) (Other academic)
    Abstract [en]

    Motivated by the recent analysis by Sano et al. 2019, Phys. Rev. Fluids, vol. 4, p. 094602, of spanwise-coherent structures in the turbulent flow around airfoils and their connection to trailing-edge noise, we carry out a thorough characterisation of such structures in three simulation databases. We analyse two different numerical simulations of incompressible flow in turbulent regime, both at chord Reynolds number of 400,000: a large-eddy simulation for a NACA 0012 profile at zero angle of attack, and a direct numerical simulation for a NACA 4412 airfoil with an angle of attack of 5 degrees. Snapshots of the flow field were analysed using Spectral Proper Orthogonal Decomposition (SPOD), in order to extract the dominant coherent structures of the flow. Focus is given to  the aforementioned spanwise-coherent fluctuations, which two-dimensional disturbances in the computational domain due to the use of periodic boundary conditions. The leading SPOD modes show that the most energetic coherent structures are wavepackets, extending over the whole turbulent boundary layers around the airfoils with significant amplitudes near the trailing-edge. Higher amplitudes are observed in the region of  stronger adverse pressure gradient at the suction side of the NACA 4412 airfoil. To understand how such structures in the turbulent field can be modelled, the linear response of the flow using the singular value decomposition of the linearised resolvent operator was performed, using the mean field as a base flow and considering a locally parallel approximation. Such analysis shows that the leading SPOD modes can be associated to optimal, linearised flow responses, particularly for stations far from the trailing edge; the latter introduces a discontinuity in boundary conditions, and the locally parallel approximation becomes questionable. We then focus on evaluating the dependence of such wavepackets on the domain size, to ensure that these structures are not an artifact of the use of periodic boundary conditions in small computational boxes. To do so, we performed an incompressible LES of a zero-pressure gradient turbulent boundary layer (ZPGTBL), for three different spanwise sizes: Lz=32 δ*, Lz=64 δ* and Lz=128 δ*, where δ* is a reference displacement thickness in a region of developed turbulent flow, with Reynolds number matching the values in the airfoil simulations. The signature of such wavepackets is seen in non-premultiplied spanwise wavenumber spectra, which reaches, for the three domain sizes, a plateau for spanwise wavelengths going to infinity (or wavenumbers going to zero); this plateau is representative of the spanwise-coherent structures seen in the airfoil simulations. Similar SPOD and resolvent analyses were carried out for the zero spanwise wavenumber of the ZPGTBL, and the same coherent wavepackets were observed for the three domains, with very similar amplitudes. Such wavepackets were also accurately modelled using the optimal resolvent response. These results confirm that the spanwise-elongated structures are not domain-size dependent for the studied simulations, and are thus a feature of turbulent boundary layers.

  • 8.
    Agrawal, Vishal
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Kulachenko, Artem
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Scapin, Nicolo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Tammisola, Outi
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim, Norway.
    An efficient isogeometric/finite-difference immersed boundary method for the fluid–structure interactions of slender flexible structures2024In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 418, article id 116495Article in journal (Refereed)
    Abstract [en]

    In this contribution, we present a robust and efficient computational framework capable of accurately capturing the dynamic motion and large deformation/deflection responses of highly-flexible rods interacting with an incompressible viscous flow. Within the partitioned approach, we adopt separate field solvers to compute the dynamics of the immersed structures and the evolution of the flow field over time, considering finite Reynolds numbers. We employ a geometrically exact, nonlinear Cosserat rod formulation in the context of the isogeometric analysis (IGA) technique to model the elastic responses of each rod in three dimensions (3D). The Navier–Stokes equations are resolved using a pressure projection method on a standard staggered Cartesian grid. The direct-forcing immersed boundary method is utilized for coupling the IGA-based structural solver with the finite-difference fluid solver. In order to fully exploit the accuracy of the IGA technique for FSI simulations, the proposed framework introduces a new procedure that decouples the resolution of the structural domain from the fluid grid. Uniformly distributed Lagrangian markers with density relative to the Eulerian grid are generated to communicate between Lagrangian and Eulerian grids consistently with IGA. We successfully validate the proposed computational framework against two- and three-dimensional FSI benchmarks involving flexible filaments undergoing large deflections/motions in an incompressible flow. We show that six times coarser structural mesh than the flow Eulerian grid delivers accurate results for classic benchmarks, leading to a major gain in computational efficiency. The simultaneous spatial and temporal convergence studies demonstrate the consistent performance of the proposed framework, showing that it conserves the order of the convergence, which is the same as that of the fluid solver.

  • 9.
    Ahn, Myeonghwan
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Karnam, A.
    Gutmark, E. J.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Flow and Near-field Pressure Fluctuations of Twin Square Jets2021In: AIAA Propulsion and Energy Forum, 2021, American Institute of Aeronautics and Astronautics Inc, AIAA , 2021Conference paper (Refereed)
    Abstract [en]

    We aim to investigate the aerodynamic and acoustics characteristics of a twin square jet using an implicit Large Eddy Simulation (ILES). A screeching cold jet condition, a nozzle pressure ratio (NPR) of 3.0, is considered to simulate a coupled twin-jet. A second-order central scheme with a modified version of Jameson’s artificial dissipation is adopted to damp numerical oscillations and to mimic the effect of small-scale turbulence without an explicit subgrid-scale (SGS) model. Numerical results show that the overall trends of time-averaged streamwise velocity profiles are similar to the experimental data, with the largest differences observed at locations associated with the presence of the shock-cell structures. A detailed investigation of the flow fluctuations in jet shear layers is performed. The amplitude of the velocity fluctuations is highly dependent on the location of the shear layers with respect to the twin-jet configuration (upper, lateral, or inner). The coupling mode of twin jets associated with the screech tone is determined as a symmetrical flapping mode be a two-points spacetime cross-correlation analysis. The overall trends of near-field pressure fluctuation spectra by LES agree well with the experimental results in both upstream and downstream regions. Near-field pressure fluctuation spectra by ILES agree well with the experimentally obtained spectra at different locations in the nozzle exit plane as well as at several downstream locations in the near-field acoustic region. The highest screech tone is observed at the inter-nozzle region where superposition of in-phase waves and standing waves are found. Fourier phase and amplitude fields at the fundamental frequency also confirm the symmetrical flapping mode of the twin jets by showing in-phase relations of hydrodynamic/acoustic waves and noise directivities. 

  • 10.
    Ahn, MyeongHwan
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Effects of Temperature on the Characteristics of Twin Square Jets by Large Eddy Simulations2022In: AIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2022, American Institute of Aeronautics and Astronautics (AIAA) , 2022, article id AIAA 2022-0681Conference paper (Refereed)
    Abstract [en]

    In this study, we investigate the effects of temperature on the aerodynamic and aeroacoustics characteristics of twin square jets. Implicit Large Eddy Simulations (ILES) are performed for twin jets with a fixed nozzle pressure ratio (NPR) of 3.0 and temperature ratios (TR) of 1.0, 2.0, 4.0, and 7.0. A second-order central scheme is used to resolve acoustic waves, and an artificial dissipation model is applied to capture shock waves and to suppress non-physical oscillations. In addition, the variation of a specific heat ratio as function of temperature is considered under the chemical equilibrium assumption. The numerical results show that the length of potential core is reduced with the increase of temperature due to the enhanced mixing in jet shear layers which can be estimated by turbulent kinetic energy (TKE). Meanwhile, the fluctuations of the transverse velocity show different trends between the cases within the corresponding potential core length, which can be associated with the screeching phenomena of the twin-jet. As temperature increases, the convection Mach number in the jet shear layers is also increased so that the Mach wave is generated for TR of 2.0, 4.0, and 7.0. However, a crackle noise is only observed for TR of 4.0 and 7.0, whose generation is identified by the skewness and kurtosis factors. Relatively low temperature jets (TR of 1.0 and 2.0) are screeching so that peaks are observed in the spectra obtained upstream. On the other hand, broadband component is gradually increased when the jets are heated, and the largest increase is observed at the location exposed to the Mach wave radiation.

  • 11.
    Ahn, MyeongHwan
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Karnam, Aatresh
    University of Cincinnati.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Large-eddy simulations of flow and aeroacoustics of twin square jets including turbulence tripping2023In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 35, no 6Article in journal (Refereed)
    Abstract [en]

    In this study, we investigate the flow and aeroacoustics of twin square (i.e., aspect ratio of 1.0) jets by implicit large-eddy simulations (LESs) under a nozzle pressure ratio of 3.0 and a temperature ratio of 1.0 conditions. A second-order central scheme coupled with a modified Jameson's artificial dissipation is used to resolve acoustics as well as to capture discontinuous solutions, e.g., shock waves. The flow boundary layer inside of the nozzle is tripped, using a small step in the convergent section of the nozzle. The time-averaged axial velocity and turbulent kinetic energy of LES with boundary layer tripping approaches better to particle image velocimetry experimental data than the LES without turbulence tripping case. A two-point space–time cross-correlation analysis suggests that the twin jets are screeching and are coupled to each other in a symmetrical flapping mode. Intense pressure fluctuations and standing waves are observed between the jets. Spectral proper orthogonal decomposition (SPOD) confirms the determined mode and the relevant wave propagation. The upstream propagating mode associated with the shock-cell structures is confined inside jets. Far-field noise obtained by solving Ffowcs Williams and Hawkings equation is in good agreement with the measured acoustic data. The symmetrical flapping mode of twin jets yields different levels of the screech tone depending on observation planes. The tonalities—the fundamental tone, second and third harmonics—appear clearly in the far-field, showing different contributions at angles corresponding to the directivities revealed by SPOD.

    Download full text (pdf)
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  • 12.
    Aihara, Aya
    et al.
    Division of Electricity, Department of Electrical Engineering, Uppsala University, Uppsala, Sweden.
    Bolin, Karl
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    Goude, Anders
    Division of Electricity, Department of Electrical Engineering, Uppsala University, Uppsala, Sweden.
    Bernhoff, Hans
    Division of Electricity, Department of Electrical Engineering, Uppsala University, Uppsala, Sweden.
    Aeroacoustic noise prediction of a vertical axis wind turbine using large eddy simulation2021In: International Journal of Aeroacoustics, ISSN 1475-472X, E-ISSN 2048-4003, Vol. 20, no 8, p. 959-978Article in journal (Refereed)
    Abstract [en]

    This study investigates the numerical prediction for the aerodynamic noise of the vertical axis wind turbine using large eddy simulation and the acoustic analogy. Low noise designs are required especially in residential areas, and sound level generated by the wind turbine is therefore important to estimate. In this paper, the incompressible flow field around the 12 kW straight-bladed vertical axis wind turbine with the rotor diameter of 6.5 m is solved, and the sound propagation is calculated based on the Ffowcs Williams and Hawkings acoustic analogy. The sound pressure for the turbine operating at high tip speed ratio is predicted, and it is validated by comparing with measurement. The measured spectra of the sound pressure observed at several azimuth angles show the broadband characteristics, and the prediction is able to reproduce the shape of these spectra. While previous works studying small-scaled vertical axis wind turbines found that the thickness noise is the dominant sound source, the loading noise can be considered to be a main contribution to the total sound for this turbine. The simulation also indicates that the received noise level is higher when the blade moves in the downwind than in the upwind side.

  • 13.
    Alarcón, José Faúndez
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Morra, Pierluigi
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Hanifi, Ardeshir
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Disturbance growth on a NACA0008 wing subjected to free stream turbulence2022In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 944, article id A44Article in journal (Refereed)
    Abstract [en]

    The stability of an incompressible boundary layer flow over a wing in the presence of free stream turbulence (FST) has been investigated by means of direct numerical simulations and compared with the linearised boundary layer equations. Four different. FST conditions have been considered, which are characterised by their turbulence intensity levels and length scales. In all cases the perturbed flow develops into elongated disturbances of high and low streamwise velocity inside the boundary layer, where their spacing has been found to be strongly dependent on the scales of the incoming free stream vorticity. The breakdown of these streaks into turbulent spots from local secondary instabilities is also observed, presenting the same development as the ones reported in flat plate experiments. The disturbance growth, characterised by its root mean squares value, is found to depend not only on the turbulence level, but also on the FST length scales. Particularly, higher disturbance growth is observed for our cases with larger length scales. This behaviour is attributed to the preferred wavenumbers that can exhibit maximum transient growth. We study this boundary layer preference by projection of the flow fields at the leading edge onto optimal disturbances. Our results demonstrate that optimal disturbance growth is the main cause of growth of disturbances on the wing boundary layer.

  • 14.
    Alenius, Emma
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    LES of acoustic-flow interaction at an orifice plate2012In: 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference), American Institute of Aeronautics and Astronautics Inc. , 2012Conference paper (Refereed)
    Abstract [en]

    The scattering of plane waves by a thick orifice plate, placed in a circular or square duct with ow, is studied through Large Eddy Simulation. The scattering matrix is computed and compared to measurements, showing reasonably good agreement except around one frequency (St ≈ 0:4). Here a stronger amplification of acoustic energy is observed in the circular duct simulations than in the measurements and the square duct simulations. In order to improve the understanding of the interaction between an incoming wave, the flow, and the plate, a few frequencies are studied in more detail. A Dynamic Mode Decomposition is performed to identify flow structures at significant frequencies. This shows that the amplification of acoustic energy occurs at the frequency where the jet in the circular duct has an axisymmetric instability. Furthermore, the incoming wave slightly amplifies this instability, and suppresses background flow fiuctuations.

  • 15.
    Alex, Alvisi
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Adalberto, Perez
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Analysis of wall-mounted hot-wire probes2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Flush-mounted cavity hot-wire probes have been around since two decades, but have typically not been applied as often compared to the traditional wall hot-wires mounted several wire diameters above the surface. While the latter suffer from heat conduction from the hot wire to the substrate in particular when used in air flows, the former is belived to significantly enhance the frequency response of the sensor. The recent work using a cavity hotwire by Gubian et al. (2019) came to the surprising conclusion that the magnitute of the fluctuating wall-shear stress τ+w,rms reaches an asymptotic value of 0.44 beyond the friction Reynolds number Re τ ∼ 600. In an effort to explain this result, which is at odds with the majority of the literature, the present work combines direct numerical simulations (DNS) of a turbulent channel flow with a cavity modelled using the immersed boundary method, as well as an experimental replication of the study of Gubian et al. in a turbulent boundary layer to explain how the contradicting results could have been obtained. It is shown that the measurements of the mentioned study can be replicated qualitatively as a result of measurement problems. We will present why cavity hot-wire probes should neither be used for quantitative nor qualitative measurements of wall-bounded flows, and that several experimental short-comings can interact to sometimes falsely yield seemingly correct results.

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  • 16.
    Alfredsson, Henrik
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Segalini, Antonio
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    The Diagnostic Plot—A Tutorial with a Ten Year Perspective2021In: Progress in Turbulence IX: Proceedings of the iTi Conference in Turbulence 2021, Springer Nature , 2021, Vol. 267, p. 125-135Conference paper (Refereed)
    Abstract [en]

    The diagnostic plot was introduced in 2010 (Eur. J. Mech. B/Fluids 29: 403–406) but was used already in 2008 during a large measurement campaign as a litmus test to determine if tripped zero-pressure gradient turbulent boundary layers fulfilled basic criteria of being canonical. It used the rms-level of streamwise velocity (urms ) in the outer part of the boundary layer, a region where urms can give clear indications if insufficient or too tough tripping has been used. In standard plots one needs both the friction velocity and measurement of the full velocity and turbulence profiles. By instead plotting urms/ U∞ as a function of U/ U∞, it was found that this gives rise to a well-defined distribution that could be used as a canonical measure. It was later discovered that it is possible to extend the description to the near wall region. It has also been extended to boundary layers over rough surfaces and with pressure gradients, and some further uses. This paper aims to be both a review of the development of the method during the last 10+ years and a tutorial for those who want to employ it in their research and maybe also find new uses of the methodology.

  • 17.
    Alghalibi, Dhiya
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. College of Engineering, University of Kufa, Al Najaf, Iraq.
    Fornari, Walter
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Rosti, Marco E.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Complex Fluids and Flows Unit, Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Onna-son, Okinawa 904-0495, Japan.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Sedimentation of finite-size particles in quiescent wall-bounded shear-thinning and Newtonian fluids2020In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 129, article id 103291Article in journal (Refereed)
    Abstract [en]

    We study the sedimentation of finite-size particles in quiescent wall-bounded Newtonian and shear-thinning fluids by interface resolved numerical simulations. The suspended phase consists of Non-Brownian rigid spherical particles with particle to fluid density ratio ρp/ρf=1.5 at three different solid volume fractions Φ=1%, 5% and 20%. Firstly, to focus on the effect of shear-thinning on the particle dynamics and interactions, the Archimedes number is increased for a single particle to have the same settling speed in the Newtonian fluid as in the shear-thinning fluid. Secondly, we consider fixed Archimedes and vary the shear-thinning properties of the fluid. Overall, we report a twofold effect of shear thinning. First and more important, the substantial increase of the particle sedimentation velocity in the shear-thinning case due to the increase of the shear rate around the particles, which reduces the local viscosity leading to a reduced particle drag. Secondly, the shear-thinning fluid reduces the level of particle interactions, causing a reduction of velocity fluctuations and resulting in particles sedimenting at approximately the same speed. Moreover, the mean settling velocities decrease with the particle concentration as a consequence of the hindering effect. Particles tend to sediment in the middle of the channel, preferentially positioning in the wake of neighbouring particles or aside them, resulting in lower levels of fluid velocity fluctuations in the gravity direction in the shear-thinning fluid.

  • 18.
    Alizad Banaei, Arash
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Rahmani, Mona
    Univ British Columbia, Dept Math, Vancouver, BC V6T 1Z2, Canada..
    Martinez, D. Mark
    Univ British Columbia, Dept Chem & Biol Engn, Vancouver, BC V6T 1Z3, Canada..
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Inertial settling of flexible fiber suspensions2020In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 5, no 2, article id 024301Article in journal (Refereed)
    Abstract [en]

    We study the inertial settling of suspensions of flexible and rigid fibers using an immersed boundary method. The fibers considered are inextensible and slender, with an aspect ratio of 20. For a single Galileo number of Ga = 160, we examine a range of dimensionless bending rigidities 0.1 < gamma < 20 and fiber concentrations 0.5 < nL(3) < 25, with n being the fiber number density and L the fiber length, that spans dilute and semidilute regimes. The settling fibers form streamers, regions where the fibers are packed and settle faster than the average settling velocity of the suspension, for nL(3) > 10. In the low-concentration regions outside the streamers, the fibers either go upward or have low settling velocities. Flexible fibers exhibit higher packing inside the streamers and smaller streamers compared to the streamers formed by the rigid fibers. Due to this higher packing, the flexible fibers settle faster compared to the rigid fibers. The formation of the streamers counterbalances the hindering of the settling velocity at higher concentrations. At higher nL(3), however, the maximum local concentration of fibers relative to a uniform distribution diminishes for both flexible and rigid fibers as the mobility of the fibers becomes limited due to the presence of other fibers in their vicinity. Due to this limited mobility, the deformation of the fibers and their settling orientation become insensitive to nL(3) for nL(3) > 7. In both the dilute and semidilute regimes, flexible fibers are more aligned with the direction perpendicular to gravity compared to rigid fibers.

  • 19.
    Alizadehgiashi, Moien
    et al.
    Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada..
    Nemr, Carine R.
    Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada..
    Chekini, Mahshid
    Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada..
    Ramos, Daniel Pinto
    Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada..
    Mittal, Nitesh
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Fluid Physics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada.
    Ahmed, Sharif U.
    Univ Toronto, Dept Pharmaceut Sci, Toronto, ON M5S 3M2, Canada..
    Khuu, Nancy
    Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada..
    Kelley, Shana O.
    Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada.;Univ Toronto, Dept Pharmaceut Sci, Toronto, ON M5S 3M2, Canada.;Univ Toronto, Inst Biomat & Biomed Engn, Toronto, ON M5S 3G9, Canada..
    Kumacheva, Eugenia
    Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada.;Univ Toronto, Inst Biomat & Biomed Engn, Toronto, ON M5S 3G9, Canada.;Univ Toronto, Dept Chem Engn & Appl Chem, Toronto, ON M5S 3E5, Canada..
    Multifunctional 3D-Printed Wound Dressings2021In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 15, no 7, p. 12375-12387Article in journal (Refereed)
    Abstract [en]

    Personalized wound dressings provide enhanced healing for different wound types; however multicomponent wound dressings with discretely controllable delivery of different biologically active agents are yet to be developed. Here we report 3D-printed multicomponent biocomposite hydrogel wound dressings that have been selectively loaded with small molecules, metal nanoparticles, and proteins for independently controlled release at the wound site. Hydrogel wound dressings carrying antibacterial silver nanoparticles and vascular endothelial growth factor with predetermined release profiles were utilized to study the physiological response of the wound in a mouse model. Compared to controls, the application of dressings resulted in improvement in granulation tissue formation and differential levels of vascular density, dependent on the release profile of the growth factor. Our study demonstrates the versatility of the 3D-printed hydrogel dressings that can yield varied physiological responses in vivo and can further be adapted for personalized treatment of various wound types.

  • 20.
    Alobud, Abdullah
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Technical Acoustics.
    The Impact of Compressor Fouling on Gas Turbine Performance and Rotordynamics2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Gas turbines can experience various changes that affect their performance.Compressor fouling is one of the leading causes that deteriorate the gas turbineperformance. This research aims to investigate the impact of compressorfouling on the performance of gas turbines and the rotodynamic behaviorof gas turbines. Fouling was simulated as a reduction of mass flow and areduction of compressor isentropic efficiency by using Turbomatch software.A rotor–bearing model was created to analyze the vibration behavior dueto compressor fouling by using MADYN 2000 software and that particledeposition leads to rotor imbalance. The results show that the main variationsfor performance are power output, pressure ratio and EGT. For the rotodynamicmodel, the result illustrates an increase in vibration level for the first andsecond bearings and a decrease for the third bearing. The results also predictedthat parameters mass flow, compressor discharge temperature or specific fuelconsumption show a similar trend compared to the increase in vibrations. Thisresult can be used in conjunction with GPA analysis to predict the foulingcondition and help in identifying the severity of the fouling condition.

  • 21.
    Amini, Kasra
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Mishra, Ases Akas
    Department of Industrial and Materials Science, Chalmers University of Technology, 412 96 Gothenburg, Sweden.
    Sivakumar, Amit Kumar
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, 412 96 Gothenburg, Sweden.
    Arlov, Dragana
    Tetra Pak Processing Systems, 221 86 Lund, Sweden.
    Innings, Fredrik
    Tetra Pak Processing Systems, 221 86 Lund, Sweden.
    Kádár, Roland
    Department of Industrial and Materials Science, Chalmers University of Technology, 412 96 Gothenburg, Sweden.
    Tammisola, Outi
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Scaling laws for near-wall flows of thixo-elasto-viscoplastic fluids in a millifluidic channel2024In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 36, no 2, article id 023107Article in journal (Refereed)
    Abstract [en]

    Thixo-elasto-viscoplastic (TEVP) fluids are very complex fluids. In addition to elasticity and viscoplasticity, they exhibit thixotropy, i.e., time-dependent rheology due to breakdown and recovery of internal structures at different length- and timescales. General and consistent methods for a priori flow prediction of TEVP fluids based on rheological characteristics are yet to be developed. We report a combined study of the rheology and flow of 18 samples of different TEVP fluids (three yogurts and three concentrations of Laponite and Carbopol, respectively, in water in both the unstirred and a stirred state). The rheology is determined both with standard protocols and with an ex situ protocol aiming at reproducing the shear history of the fluid in the flow. Micrometer resolution flow measurements in a millimeter scale rectangular duct are performed with Doppler Optical Coherence Tomography (D-OCT). As expected, the results show the existence of a plug flow region for samples with sufficiently high yield stress. At low flow rates, the plug extends almost all the way to the wall and the extent of the plug decreases not only with increased flow rate but also with increased thixotropy. The ex situ rheology protocol enables estimation of the shear rate and shear stress close to the wall, making it possible to identify two scaling laws that relates four different non-dimensional groups quantifying the key properties wall-shear stress and slip velocity. The scaling laws are suggested as an ansatz for a priori prediction of the near-wall flow of TEVP fluids based on shear flow-curves obtained with a rheometer.

  • 22.
    Amini, Kasra
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Moradi, Mojgan
    Department of Architectural Technology, Faculty of Architecture and Urban Planning, University of Art, Tehran, Iran.
    Vossoughi, Bahareh
    Faculty of Mechanical Engineering, RWTH Aachen University, Aachen, Germany.
    Janabadi, Ehsan Dehghani
    Department of Architectural Technology, Faculty of Architecture and Urban Planning, University of Art, Tehran, Iran.
    Space-technological and architectural methodology and process towards design of long-term habitats for scientific human missions on mars2023In: MethodsX, ISSN 1258-780X, E-ISSN 2215-0161, Vol. 11, article id 102270Article in journal (Refereed)
    Abstract [en]

    Centered on the core idea of long duration habitat design for research crew on Mars, the Martian Habitat Units (MHUs) are designed as a cluster of 10 units each with the maximum capacity of 9 crew members to live and carry on with the local challenges of scientific and exploratory life, while enjoying their lives as intellectual, social individuals in the harsh environment of Mars for durations in the order of magnitude of several years. This approach to the concept of a living environment in sharp contradiction to that of a shelter with the minimal capabilities to meet the requirements of terrestrial life to the point of survival, has led the outcoming design to be a fulfilling environment for the inhabitants of the units to evolve and thrive culturally, while being on a years-long mission. This manuscript provides detailed insight on the lessons learned of the aforementioned comprehensive design attempt with, but not limited to, the following core concerns: • The initial stand-point of such a design procedure relies on an ever increasing and comprehensive list of concerns, be it classically discussed in the literature and predictable, or unforeseen on the face of it, but to be prevented anyhow. The manuscript discusses the most crucial ones of such criteria/concerns. • The infamous saying of “Whatever that can go wrong, will go wrong” demands a rather complex level of redundancies in all layers of the design and the thought procedure behind its all aspects. The manuscript addresses the adequate steps towards its realization. • Modularity in all layers of the design plays a key role in reducing construction, maintenance, and installation costs, as for any deep space mission the mentioned expenses are astronomically high themselves. The manuscript presents our solution for geometric modularity of the design.

  • 23.
    Amiri, A.
    et al.
    Eindhoven Univ Technol, Dept Mech Engn, NL-5600 MB Eindhoven, Netherlands.;Eindhoven Univ Technol, Inst Complex Mol Syst, NL-5600 MB Eindhoven, Netherlands..
    Caasenbrood, B.
    Eindhoven Univ Technol, Dept Mech Engn, NL-5600 MB Eindhoven, Netherlands..
    van de Wouw, N.
    Eindhoven Univ Technol, Dept Mech Engn, NL-5600 MB Eindhoven, Netherlands..
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    A replacement model to simulate the nonlinear dynamics of electro-responsive liquid crystal coatings2023In: AIP Advances, E-ISSN 2158-3226, Vol. 13, no 3, article id 035203Article in journal (Refereed)
    Abstract [en]

    An electric circuit replacement model is proposed to simulate the key nonlinear dynamics of electro-responsive liquid crystal polymer networks (LCNs). LCNs are known for having great potential to be integrated into smart functional surfaces due to their ability to generate various surface patterns. However, due to their complex molecular dynamics, low-order dynamic models that can accurately describe and predict their dynamic behavior are still lacking. In light of this research gap, we develop a lumped-parameter replacement model based on the observed dynamics in the experimental data and the physics of LCN dielectric properties. The unique assembly of lumped parameters in its simplest form describes the transformation of a high-frequency input voltage to a relatively slow increase in the local height of the LCN coating in between the electrodes, serving as an excitation mechanism to induce height change. The nonlinear dynamics of this height increase, as a function of both excitation frequency and voltage, is described by the proposed model. Furthermore, the comparison of the simulation results with the experimental data from LCN shows that key LCN response characteristics are captured well by the model. This model makes it possible to accurately predict and control the response of the electro-responsive LCN surfaces to obtain a predefined desired deformation pattern, which is a vital requirement for integrating them in haptic and smart surface devices.

  • 24.
    Amo-Navarro, Jesus
    et al.
    Univ Politecn Valencia, Inst Univ Matemat Pura & Aplicada, Valencia 46022, Spain..
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Conejero, J. Alberto
    Univ Politecn Valencia, Inst Univ Matemat Pura & Aplicada, Valencia 46022, Spain..
    Hoyas, Sergio
    Univ Politecn Valencia, Inst Univ Matemat Pura & Aplicada, Valencia 46022, Spain..
    Two-Dimensional Compact-Finite-Difference Schemes for Solving the bi-Laplacian Operator with Homogeneous Wall-Normal Derivatives2021In: Mathematics, E-ISSN 2227-7390, Vol. 9, no 19, article id 2508Article in journal (Refereed)
    Abstract [en]

    In fluid mechanics, the bi-Laplacian operator with Neumann homogeneous boundary conditions emerges when transforming the Navier-Stokes equations to the vorticity-velocity formulation. In the case of problems with a periodic direction, the problem can be transformed into multiple, independent, two-dimensional fourth-order elliptic problems. An efficient method to solve these two-dimensional bi-Laplacian operators with Neumann homogeneus boundary conditions was designed and validated using 2D compact finite difference schemes. The solution is formulated as a linear combination of auxiliary solutions, as many as the number of points on the boundary, a method that was prohibitive some years ago due to the large memory requirements to store all these auxiliary functions. The validation has been made for different field configurations, grid sizes, and stencils of the numerical scheme, showing its potential to tackle high gradient fields as those that can be found in turbulent flows.

  • 25.
    Amor, Christian
    et al.
    Univ Politecn Madrid, Sch Aerosp Engn, Madrid 28040, Spain..
    Perez, Jose M.
    Univ Politecn Madrid, Sch Aerosp Engn, Madrid 28040, Spain..
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Le Clainche, Soledad
    Univ Politecn Madrid, Sch Aerosp Engn, Madrid 28040, Spain..
    Modeling the Turbulent Wake Behind a Wall-Mounted Square Cylinder2020In: Logic journal of the IGPL (Print), ISSN 1367-0751, E-ISSN 1368-9894, Vol. 30, no 2, p. 263-276Article in journal (Refereed)
    Abstract [en]

    This article introduces some soft computing methods generally used for data analysis and flow pattern detection in fluid dynamics. These techniques decompose the original flow field as an expansion of modes, which can be either orthogonal in time (variants of dynamic mode decomposition), or in space (variants of proper orthogonal decomposition) or in time and space (spectral proper orthogonal decomposition), or they can simply be selected using some sophisticated statistical techniques (empirical mode decomposition). The performance of these methods is tested in the turbulent wake of a wall-mounted square cylinder. This highly complex flow is suitable to show the ability of the aforementioned methods to reduce the degrees of freedom of the original data by only retaining the large scales in the flow. The main result is a reduced-order model of the original flow case, based on a low number of modes. A deep discussion is carried out about how to choose the most computationally efficient method to obtain suitable reduced-order models of the flow. The techniques introduced in this article are data-driven methods that could be applied to model any type of non-linear dynamical system, including numerical and experimental databases.

  • 26.
    Amor, Christian
    et al.
    Technol Grad Univ, Okinawa Inst Sci, Complex Fluids & Flows Unit, 1919-1 Tancha, Onna, Okinawa 9040495, Japan..
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Le Clainche, Soledad
    Univ Politecn Madrid, ETSI Aeronaut & Espacio, Plaza Cardenal Cisneros 3, Madrid 28040, Spain..
    Higher-order dynamic mode decomposition on-the-fly: A low-order algorithm for complex fluid flows2023In: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 475, article id 111849Article in journal (Refereed)
    Abstract [en]

    This article presents a new method to identify the main patterns describing the flow motion in complex flows. The algorithm is an extension of the higher-order dynamic mode decomposition (HODMD), which compresses the snapshots from the analysed database and progressively updates new compressed snapshots on-the-fly, so it is denoted as HODMD on -the-fly (HODMD-of). This algorithm can be applied in parallel to the numerical simulations (or experiments), and it exhibits two main advantages over offline algorithms: (i) it automatically selects on-the-fly the number of necessary snapshots from the database to identify the relevant dynamics; and (ii) it can be used from the beginning of a numerical simulation (or experiment), since it uses a sliding-window to automatically select, also on-the-fly, the suitable interval to perform the data analysis, i.e. it automatically identifies and discards the transient dynamics. The HODMD-of algorithm is suitable to build reduced order models, which have a much lower computational cost than the original simulation. The performance of the method has been tested in three different cases: the axi-symmetric synthetic jet, the three-dimensional wake of a circular cylinder and the turbulent wake behind a wall-mounted square cylinder. The obtained speed-up factors are around 7 with respect to HODMD; this value depends on the simulation and the configuration of the hyperparameters. HODMD-of also provides a significant reduction of the memory requirements, between 40 - 80% amongst the two-and three-dimensional cases studied in this paper.

  • 27. Ananthaseshan, S.
    et al.
    Bojakowski, K.
    Sacharczuk, M.
    Poznanski, P.
    Skiba, D. S.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Tillämpad strömningsmekanik.
    MacKenzie, Jordan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Szkulmowska, A.
    Berg, Niclas
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Tillämpad strömningsmekanik.
    Andziak, P.
    Menkens, H.
    Wojtkowski, M.
    Religa, D.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Guzik, T.
    Gaciong, Z.
    Religa, P.
    Red blood cell distribution width is associated with increased interactions of blood cells with vascular wall2022In: Scientific Reports, E-ISSN 2045-2322, Vol. 12, no 1, article id 13676Article in journal (Refereed)
    Abstract [en]

    The mechanism underlying the association between elevated red cell distribution width (RDW) and poor prognosis in variety of diseases is unknown although many researchers consider RDW a marker of inflammation. We hypothesized that RDW directly affects intravascular hemodynamics, interactions between circulating cells and vessel wall, inducing local changes predisposing to atherothrombosis. We applied different human and animal models to verify our hypothesis. Carotid plaques harvested from patients with high RDW had increased expression of genes and proteins associated with accelerated atherosclerosis as compared to subjects with low RDW. In microfluidic channels samples of blood from high RDW subjects showed flow pattern facilitating direct interaction with vessel wall. Flow pattern was also dependent on RDW value in mouse carotid arteries analyzed with Magnetic Resonance Imaging. In different mouse models of elevated RDW accelerated development of atherosclerotic lesions in aortas was observed. Therefore, comprehensive biological, fluid physics and optics studies showed that variation of red blood cells size measured by RDW results in increased interactions between vascular wall and circulating morphotic elements which contribute to vascular pathology.

  • 28.
    Andersson, David
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    Acoustic properties of a 5G Telecom Equipment Shroud Design for Noise suppression2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    As technology moves forward it has a tendency to consume more and more power that needs to be cooled by bigger and louder fans, this is especially true for the new generation of 5G radio equipment. This Master thesis is a collaboration with Ericsson and attempts to construct a shroud for containing a number of 5G radio units whilst attenuating the fan noise of the units as effectively as possible. In this project are air ducts used and at the ends silencers are created utilizing the Cremer impedance; the optimal wall impedance for damping an acoustic mode of a propagating wave. To predict the result, a simplified model in an acoustic FEM program was also explored and compared to the sound level of the constructed shroud. The finished shroud successfully reduces the noise of the radio units by 13 dB(A) while causing an increase in temperature of between 2.8°C to 5.9°C. This result was deemed to be a success and the Cremer impedance approach of reducing noise is therefore advised for future development.

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  • 29.
    Andreolli, Andrea
    et al.
    Karlsruhe Inst Technol, Inst Fluid Mech, Kaiserstr 10, D-76131 Karlsruhe, Germany..
    Gatti, Davide
    Karlsruhe Inst Technol, Inst Fluid Mech, Kaiserstr 10, D-76131 Karlsruhe, Germany..
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. Karlsruhe Inst Technol, Karlsruhe, Germany..
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Separating large-scale superposition and modulation in turbulent channels2023In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 958, article id A37Article in journal (Refereed)
    Abstract [en]

    The presence of very-large-scale motions in wall-bounded turbulent flows is commonly associated with their footprint in the form of the superposition of the large scales at the wall and the additional amplitude modulation of small-scale near-wall turbulence. These two phenomena are currently understood to be interlinked, with the superposed large-scale velocity gradient causing the modulation of small-scale activity in the proximity of the wall. To challenge this idea, we devise a numerical strategy that selectively suppresses either superposition or amplitude modulation, in an effort to isolate and study the remaining phenomenon. Results from our direct numerical simulations indicate that a positive correlation between the amplitude of the small scales in the near-wall region and the large-scale signal in the outer flow persists even when near-wall large-scale motions are suppressed - i.e. in absence of superposition. Clearly, this kind of correlation cannot be caused by the near-wall large-scale velocity or its gradients, as both are absent. Conversely, when modulation is blocked, the near-wall footprints of the large scales seem to disappear. This study has been carried out on channel flows at friction Reynolds number Re-tau = 1000 in both standard simulation domains and minimal streamwise units (MSUs), where the streamwise fluctuation energy is enhanced. The consistency of the results obtained by the two approaches suggests that MSUs can capture correctly this kind of scale interaction at a much reduced cost.

  • 30.
    Apazidis, Nicholas
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Sundarapandian, Sembian
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Liverts, Michael
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Supersonic jet by blast wave focusing2021In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 33, no 12, p. 126101-, article id 126101Article in journal (Refereed)
    Abstract [en]

    A supersonic jet of Mach number M = 4.5 in air is produced experimentally at the apex of a miniature 150 x 50 x 5 mm converging section with a 2 x 5 mm opening by the principle of blast wave amplification through focusing. An initial plane blast wave of M = 2.4 in the convergence section is generated by the exploding wire technique. The profile of the convergence section is specially tailored to smoothly transform a plane blast wave into a perfectly cylindrical arc, imploding at the apex of the section. The cylindrical form of the imploding shock delivers maximum shock amplification in the two-dimensional test section and maximum subsequent jet flow velocity behind the shock front. Blast wave propagation in the convergence chamber as well as jet generation through a 2 mm opening at the apex into the adjacent exhaust chamber is optically captured by a high-speed camera using the shadowgraph method. Visualizing the flow provided a distinct advantage not only for obtaining detailed information on the flow characteristics but also for validating the numerical scheme which further enhanced the analysis. Experimental images together with the numerical analysis deliver detailed information on the blast wave propagation and focusing as well as subsequent jet initiation and development. One of the main advantages of the described method apart from being simple and robust is the effective focusing of low initial input energy levels of just around 500 Joules, resulting in production of supersonic jets in a small confined chamber.

  • 31.
    Appelquist, Ellinor
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Lingwood, Rebecca
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Transition to turbulence in the rotating-disk boundary layer2020In: ETC 2013 - 14th European Turbulence Conference, Zakon Group LLC , 2020Conference paper (Refereed)
    Abstract [en]

    The development of the flow over a rotating disk is investigated by direct numerical simulations using both the linearised and fully nonlinear Navier-Stokes equations. The nonlinear simulations allow investigation of the transition to turbulence of the realistic spatially-developing boundary layer, and these simulations can be directly validated by physical experiments of the same case. The current research aims to elucidate further the global stability properties of the flow. So far, there are no conclusive simulations available in the literature for the fully nonlinear case for this flow, and since the nonlinearity is particularly relevant for transition to turbulence an increased understanding of this process is expected. 

  • 32.
    Arteaga, Ines L.
    et al.
    Dynamics and Control Group, Mechanical Engineering Department, Eindhoven University of Technology, 5612 AZ Eindhoven, Netherlands.
    Rissmann, Martin
    Vibratec 28 Chemin du Petit Bois, 69130 Ecully Cedex, France.
    Garralaga, Miguel Ángel
    Metro de Madrid, Calle Néctar s/n, 28022 Madrid, Spain.
    Thompson, David
    Institute of Sound and Vibration Research, University of Southampton, Southampton SO17 1BJ, UK.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    Cierco, Ester
    Ingeniería para el Control del Ruido SL, Berruguete 52 08035 Barcelona, Spain.
    Dittrich, Michael
    TNO Acoustics and Sonar, Oude Waalsdorperweg 63, 2592 AK, The Hague, The Netherlands.
    Sarradj, Ennes
    Technische Universität Berlin, Strabe des 17. Juni 135, 10623 Berlin, Germany.
    Garcia, Marta
    UNIFE, Union des Industries Ferroviaires Européennes, Avenue Louise 221-B 1050 Brubels, Belgium.
    The TRANSIT project: innovation towards train pass-by noise source characterisation and separation tools2023In: 2022 Conference Proceedings Transport Research Arena, TRA Lisbon 2022, Elsevier B.V. , 2023, Vol. 72, p. 989-996Conference paper (Refereed)
    Abstract [en]

    In TRANSIT, experimental methods are developed to separate and characterise noise sources on moving trains. Improved microphone array techniques allow quantification of sound power and directivity. Source separation methods based on the Pass-By Analysis method, Advanced Transfer Path Analysis and the TWINS model are also developed. For trains at standstill, new test methods are developed to quantify noise transmission paths from sources to the standard microphone positions accounting for installation effects. Several measurement campaigns are used to demonstrate and verify these methods. In addition, innovative materials and methods are investigated for improved sound comfort in trains. Approaches considered include optimal sound absorption at the source, attenuation along ducts for air conditioning systems and innovative meta-structure designs for the car-body parts.

  • 33.
    Assenai, Tagiadin
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Technical Acoustics.
    Epidemiological survey of moderators moderators for railway noise annoyance2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The disturbance caused by railway noise has been investigated in this paper. A total of 127residents living near the Västra Stambanan were interviewed, and the noise levels from NordiskaBeräkningsmodellen were compared with the perceived disturbance. The results of the studyindicate a correlation between indoor noise levels and disturbance. The activities that peoplereported as being affected were meals, relaxation, sleep, and conversations in decreasing order.

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    fulltext
  • 34.
    Atif, Abdul-Raouf
    et al.
    Uppsala Univ, Dept Mat Sci & Engn, S-75122 Uppsala, Sweden..
    Lacis, Ugis
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Engqvist, Håkan
    Uppsala Univ, Dept Mat Sci & Engn, S-75122 Uppsala, Sweden..
    Tenje, Maria
    Uppsala Univ, Dept Mat Sci & Engn, S-75122 Uppsala, Sweden.;Uppsala Univ, Sci Life Lab, S-75122 Uppsala, Sweden..
    Bagheri, Shervin
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Mestres, Gemma
    Uppsala Univ, Dept Mat Sci & Engn, S-75122 Uppsala, Sweden.;Uppsala Univ, Sci Life Lab, S-75122 Uppsala, Sweden..
    Experimental Characterization and Mathematical Modeling of the Adsorption of Proteins and Cells on Biomimetic Hydroxyapatite2022In: ACS Omega, E-ISSN 2470-1343, Vol. 7, no 1, p. 908-920Article in journal (Refereed)
    Abstract [en]

    Biomaterial development is a long process consisting of multiple stages of design and evaluation within the context of both in vitro and in vivo testing. To streamline this process, mathematical and computational modeling displays potential as a tool for rapid biomaterial characterization, enabling the prediction of optimal physicochemical parameters. In this work, a Langmuir isotherm-based model was used to describe protein and cell adhesion on a biomimetic hydroxyapatite surface, both independently and in a one-way coupled system. The results indicated that increased protein surface coverage leads to improved cell adhesion and spread, with maximal protein coverage occurring within 48 h. In addition, the Langmuir model displayed a good fit with the experimental data. Overall, computational modeling is an exciting avenue that may lead to savings in terms of time and cost during the biomaterial development process.

  • 35. Atzori, M.
    et al.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Control effects on coherent structures in a non-uniform adverse-pressure-gradient boundary layer2022In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 97, article id 109036Article in journal (Refereed)
    Abstract [en]

    We examine the effects of three basic but effective control strategies, namely uniform blowing, uniform suction, and body-force damping, on the intense Reynolds-stress events in the turbulent boundary layer (TBL) developing on the suction side of a NACA4412 airfoil. This flow is subjected to a non-uniform adverse pressure gradient (APG), which substantially modifies its turbulence statistics with respect to a zero-pressure-gradient (ZPG) boundary layer, and it also changes how control strategies affect the flow. The strong APG results in intense events that are shorter and more often detached from the wall than in ZPG TBLs. In a quadrant analysis, ejections remain the most relevant structures, but sweeps become more important than in ZPG TBLs, a fact that results in a lower contribution to the wall-normal velocity from intense Reynolds-stress events. Control effects are relatively less important on intense events than on the turbulent statistics. Uniform blowing has an impact similar to that of an even more intense APG, while uniform suction has more complex effects, most likely due to the particular behavior of the wall-normal velocity component near the wall. Body-force damping also reduces the probability of occurrence of very-large attached structures and that of intense events in the proximity of the actuation region. Our results show that intense Reynolds-stress events are robust features of the flow. If control strategies do not target directly these structures, their effects on the strong events is less pronounced than the effects on the mean flow. 

  • 36.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Köpp, Wiebke
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Chien, Wei Der
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Massaro, Daniele
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Mallor, Fermin
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Peplinski, Adam
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Rezaei, Mohamad
    PDC Center for High Performance Computing, KTH Royal Institute of Technology.
    Jansson, Niclas
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Markidis, Stefano
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Laure, Erwin
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Weinkauf, Tino
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    In-situ visualization of large-scale turbulence simulations in Nek5000 with ParaView Catalyst2021Report (Other academic)
    Abstract [en]

    In-situ visualization on HPC systems allows us to analyze simulation results that would otherwise be impossible, given the size of the simulation data sets and offline post-processing execution time. We design and develop in-situ visualization with Paraview Catalyst in Nek5000, a massively parallel Fortran and C code for computational fluid dynamics applications. We perform strong scalability tests up to 2,048 cores on KTH's Beskow Cray XC40 supercomputer and assess in-situ visualization's impact on the Nek5000 performance. In our study case, a high-fidelity simulation of turbulent flow, we observe that in-situ operations significantly limit the strong scalability of the code, reducing the relative parallel efficiency to only ~21\% on 2,048 cores (the relative efficiency of Nek5000 without in-situ operations is ~99\%). Through profiling with Arm MAP, we identified a bottleneck in the image composition step (that uses Radix-kr algorithm) where a majority of the time is spent on MPI communication. We also identified an imbalance of in-situ processing time between rank 0 and all other ranks. Better scaling and load-balancing in the parallel image composition would considerably improve the performance and scalability of Nek5000 with in-situ capabilities in large-scale simulation.

  • 37.
    Atzori, Marco
    et al.
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Mallor, Fermin
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Pozuelo, Ramon
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Fukagata, Koji
    Department of Mechanical Engineering, Keio University, 223-8522 Yokohama, Japan.
    Vinuesa, Ricardo
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Schlatter, Philipp
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    A new perspective on skin-friction contributions in adverse-pressure-gradient turbulent boundary layersManuscript (preprint) (Other academic)
    Abstract [en]

    For adverse-pressure-gradient turbulent boundary layers, the study of integral skin-friction contributions still poses significant challenges. Beyond questions related to the integration boundaries and the derivation procedure, which have been thoroughly investigated in the literature, an important issue is how different terms should be aggregated. The nature of these flows, which exhibit significant in-homogeneity in the streamwise direction, usually results in cancellation between several contributions with high absolute values. We propose a formulation of the identity derived by Fukagata, Iwamoto \& Kasagi (Phys. Fluids, vol. 14, 2002, pp. 73--76), which we obtained from the convective form of the governing equations. A new skin-friction contribution is defined, considering wall-tangential convection and pressure gradient together. This contribution is related to the evolution of the dynamic pressure in the mean flow. The results of the decomposition are examined for a broad range of pressure-gradient conditions and different flow-control strategies. We found that the new formulation of the identity allows to readily identify the different regimes of near-equilibrium conditions and approaching separation. It also provides a more effective description of control effects. A similar aggregation between convection and pressure-gradient terms is also possible for any other decomposition where in-homogeneity contributions are considered explicitly. 

  • 38.
    Atzori, Marco
    et al.
    Johannes Kepler Univ Linz, Dept Particulate Flow Modelling, A-4040 Linz, Austria..
    Mallor, Fermin
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Pozuelo, Ramon
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fukagata, Koji
    Keio Univ, Dept Mech Engn, Yokohama 2238522, Japan..
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    A new perspective on skin-friction contributions in adverse-pressure-gradient turbulent boundary layers2023In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 101, article id 109117Article in journal (Refereed)
    Abstract [en]

    For adverse-pressure-gradient turbulent boundary layers, the study of integral skin-friction contributions still poses significant challenges. Beyond questions related to the integration boundaries and the derivation procedure, which have been thoroughly investigated in the literature, an important issue is how different terms should be aggregated. The nature of these flows, which exhibit significant in-homogeneity in the streamwise direction, usually results in cancellation between several contributions with high absolute values. We propose a formulation of the identity derived by Fukagata et al. (2002), which we obtained from the convective form of the governing equations. A new skin-friction contribution is defined, considering wall-tangential convection and pressure gradient together. This contribution is related to the evolution of the dynamic pressure in the mean flow. The results of the decomposition are examined for a broad range of pressure-gradient conditions and different flow-control strategies. We found that the new formulation of the identity allows to readily identify the different regimes of near-equilibrium conditions and approaching separation. It also provides a more effective description of control effects. A similar aggregation between convection and pressure-gradient terms is also possible for any other decomposition where in-homogeneity contributions are considered explicitly.

  • 39.
    Atzori, Marco
    et al.
    Johannes Kepler Univ Linz, Dept Particulate Flow Modelling, A-4040 Linz, Austria..
    Torres, Pablo
    Univ Politecn Valencia, Inst Univ Matemat Pura & Aplicada, Valencia 46022, Spain..
    Vidal, Alvaro
    Parallel Works, Chicago, IL 60654 USA..
    Le Clainche, Soledad
    Univ Politecn Madrid, Sch Aerosp Engn, Madrid 28040, Spain..
    Hoyas, Sergio
    Univ Politecn Valencia, Inst Univ Matemat Pura & Aplicada, Valencia 46022, Spain..
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    High-resolution simulations of a turbulent boundary layer impacting two obstacles in tandem2023In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 8, no 6, article id 063801Article in journal (Refereed)
    Abstract [en]

    High-fidelity large-eddy simulations of the flow around two rectangular obstacles are carried out at a Reynolds number of 10 000 based on the freestream velocity and the obstacle height. The incoming flow is a developed turbulent boundary layer. Mean-velocity components, turbulence fluctuations, and the terms of the turbulent-kinetic-energy budget are analyzed for three flow regimes: skimming flow, wake interference, and isolated roughness. Three regions are identified where the flow undergoes the most significant changes: the first obstacle's wake, the region in front of the second obstacle, and the region around the second obstacle. In the skimming-flow case, turbulence activity in the cavity between the obstacles is limited and mainly occurs in a small region in front of the second obstacle. In the wake-interference case, there is a strong interaction between the freestream flow that penetrates the cavity and the wake of the first obstacle. This interaction results in more intense turbulent fluctuations between the obstacles. In the isolated-roughness case, the wake of the first obstacle is in good agreement with that of an isolated obstacle. Separation bubbles with strong turbulent fluctuations appear around the second obstacle.

  • 40.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Fahland, G.
    Stroh, A.
    Gatti, D.
    Frohnapfel, B.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Aerodynamic Effects of Uniform Blowing and Suction on a NACA4412 Airfoil2020In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987Article in journal (Refereed)
    Abstract [en]

    We carried out high-fidelity large-eddy simulations to investigate the effects of uniform blowing and uniform suction on the aerodynamic efficiency of a NACA4412 airfoil at the moderate Reynolds number based on chord length and incoming velocity of Rec= 200 , 000. We found that uniform blowing applied at the suction side reduces the aerodynamics efficiency, while uniform suction increases it. This result is due to the combined impact of blowing and suction on skin friction, pressure drag and lift. When applied to the pressure side, uniform blowing improves aerodynamic efficiency. The Reynolds-number dependence of the relative contributions of pressure and friction to the total drag for the reference case is analysed via Reynolds-averaged Navier–Stokes simulations up to Rec= 10 , 000 , 000. The results suggest that our conclusions on the control effect can tentatively be extended to a broader range of Reynolds numbers. 

  • 41.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Gatti, D.
    Stroh, A.
    Frohnapfel, B.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Effects of Different Friction Control Techniques on Turbulence Developing Around Wings2020In: ERCOFTAC Workshop Direct and Large Eddy Simulation: Direct and Large Eddy Simulation XII, Springer, 2020, p. 305-311Chapter in book (Refereed)
    Abstract [en]

    Developing efficient flow control techniques remain a challenging task due to the complexity of turbulent flows in industrial applications, a relevant example of which are turbulent boundary layers (TBL) subjected to pressure gradients. In the present study, we employ high-fidelity numerical simulations to assess the impact of different control strategies on the flow around a NACA4412 airfoil at a Reynolds number Rec=200,000 based on the chord length c and the inflow velocity U∞. The choice of this specific study case is motivated by the relatively weak dependence of the pressure distribution around the airfoil on the Reynolds number [6], which allows distinguishing the effects of increasing Reynolds number and those of the non-uniform adverse pressure gradient (APG).

  • 42.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Lozano-Durán, A.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Contribution of Reynolds-stress structures to the secondary flow in turbulent ducts2019In: 11th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2019, International Symposium on Turbulence and Shear Flow Phenomena, TSFP , 2019Conference paper (Refereed)
    Abstract [en]

    The present work is aimed at evaluating the contribution to the secondary flow in duct flow with square and rectangular cross section from three-dimensional coherent structures, defined as intense Reynolds-stress events. The contribution to a certain mean quantity is defined as the ensemble average over the detected coherent structures, weighted with their own occupied volume fraction. Our analysis unveils that the contribution to the cross-stream components of the mean velocity is either very similar to the same contribution in channel flow, or almost negligible in respect to the contribution from the portion of the domain not occupied by coherent structures. These results suggest that the most intense events are not directly responsible for the secondary flow.

  • 43.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Lozano-Durán, Adrián
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Coherent structures in turbulent boundary layers over an airfoil2020In: Journal of Physics: Conference Series, ISSN 1742-6588, Vol. 1522, article id 012020Article in journal (Refereed)
    Abstract [en]

    This preliminary study is concerned with the identification of three-dimensional coherent structures, defined as intense Reynolds-stress events, in the turbulent boundary layer developing over the suction side of a NACA4412 airfoil at a Reynolds number based on the chord length and the incoming velocity of $Re_c=200,000$. The scientific interest for such flows originates from the non-uniform adverse pressure gradient that affects the boundary-layer development. Firstly, we assess different methods to identify the turbulent-non-turbulent interface, in order to exclude the irrotational region from the analysis. Secondly, we evaluate the contribution of the considered coherent structures to the enhanced wall-normal velocity, characteristic of adverse pressure gradients. Our results show that it is necessary to limit the detection of coherent structures to the turbulent region of the domain, and that the structures reveal qualitative differences between the contributions of intense events to the wall-normal velocity in adverse-pressure-gradient and zero-pressure-gradient turbulent boundary layers.

  • 44.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Lozano-Durán, Adrián
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Intense Reynolds-stress events in turbulent ducts2021In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 89, article id 108802Article in journal (Refereed)
    Abstract [en]

    The aim of the present work is to investigate the role of intense Reynolds shear-stress events in the generation of the secondary flow in turbulent ducts. We consider the connected regions of flow where the product of the instantaneous fluctuations of two velocity components is higher than a threshold based on the long-time turbulence statistics, in the spirit of the three-dimensional quadrant analysis proposed by Lozano-Dur\'an \textit{et al.} (\textit{J.~Fluid Mech.}, vol. 694, 2012, pp. 100--130). We examine both the geometrical properties of these structures and their contribution to the mean in-plane velocity components, and we perform a comparison with turbulent channel flow at similar Reynolds number. The contribution to a certain mean quantity is defined as the ensemble average over the detected coherent structures, weighted with their own occupied volume fraction. In the core region of the duct, the contribution of intense events to the wall-normal component of the mean velocity is in very good agreement with that in the channel, despite the presence of the secondary flow in the former. Additionally, the shapes of the three-dimensional objects do not differ significantly in both flows. In the corner region of the duct, the proximity of the walls affects both the geometrical properties of the coherent structures and the contribution to the mean component of the vertical velocity. However, such contribution is less relevant than that of the complementary portion of the flow not included in such objects. Our results show that strong Reynolds shear-stress events are affected by the presence of a corner but, despite the important role of these structures in the dynamics of wall-bounded turbulent flows, their contribution to the secondary flow is relatively low, both in the core and in the corner.

  • 45.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Control effects on coherent structures in a non-uniform adverse-pressure-gradient boundary layer2021Report (Other academic)
    Abstract [en]

    In the present report, we examine the effects of three control strategies, namely uniform blowing, uniform suction, and body-force damping, on the intense Reynolds-stress events in the turbulent boundary layer (TBL) developing on the suction side of a NACA4412 airfoil. This flow is subjected to a non-uniform adverse pressure gradient (APG), which substantially modifies its turbulence statistics with respect to a zero-pressure-gradient (ZPG) boundary layer, and it also changes how control strategies affect the flow. We found that the strong APG results in intense events that are shorter and more often detached from the wall than in ZPG TBLs, and it also modified the contributions of different quadrants. Ejections remain the most relevant structures, but sweeps become more important than in ZPG TBLs, a fact that results in a lower contribution to the wall-normal vertical velocity from intense events. We found that control effects are relatively less important on intense events than on the turbulent statistics. Uniform blowing has an impact similar to that of an even more intense APG, while uniform suction has more complex effects, most likely due to the particular behavior of the wall-normal velocity component near the wall. Body-force damping also reduces the probability of occurrence of very-large attached structures and, not surprisingly, that of intense events in the proximity of the actuation region. 

  • 46.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Stroh, Alexander
    Institute of Fluid Mechanics, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany.
    Gatti, Davide
    Institute of Fluid Mechanics, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany.
    Frohnapfel, Bettina
    Institute of Fluid Mechanics, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Blowing and suction applied to non-uniform adverse-pressure-gradient boundary layers2021Report (Other academic)
    Abstract [en]

    An extensive parametric study of turbulent boundary layer control on airfoils via uniform blowing or suction is presented. The control is applied on either suction or pressure side of several 4-digit NACA-series airfoils. The considered parameter variations include angle of attack, Reynolds number, control intensity, airfoil camber and airfoil thickness. Two comprehensive metrics, designed to account for the additional energy required by the control, are introduced to evaluate the net aerodynamic performance enhancements. The study confirms previous findings for suction side boundary layer control and demonstrates the interesting potential of blowing on the pressure side under various conditions, which achieves a maximum total net drag saving of 14% within the considered parameter space. The broad parameter space covered by the presented Reynolds-average Navier-Stokes (RANS) simulations allows for more general conclusions than previous studies and can thus provide guidelines for the design of future detailed experimental or numerical studies on similar boundary layer control schemes.

  • 47.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Stroh, Alexander
    Karlsruhe Techonol, Inst Fluid Mech, D-76131 Karlsruhe, Germany..
    Gatti, Davide
    Karlsruhe Techonol, Inst Fluid Mech, D-76131 Karlsruhe, Germany..
    Frohnapfel, Bettina
    Karlsruhe Techonol, Inst Fluid Mech, D-76131 Karlsruhe, Germany..
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Uniform blowing and suction applied to nonuniform adverse-pressure-gradient wing boundary layers2021In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 6, no 11, article id 113904Article in journal (Refereed)
    Abstract [en]

    A detailed analysis of the effects of uniform blowing, uniform suction, and body-force damping on the turbulent boundary layer developing around a NACA4412 airfoil at moderate Reynolds number is presented. The flow over the suction and the pressure sides of the airfoil is subjected to a nonuniform adverse pressure gradient and a moderate favorable pressure gradient, respectively. We find that the changes in total skin friction due to blowing and suction are not very sensitive to different pressure-gradient conditions or the Reynolds number. However, when blowing and suction are applied to an adverse-pressure-gradient (APG) boundary layer, their impact on properties such as the boundary-layer thickness, the intensity of the wall-normal convection, and turbulent fluctuations are more pronounced. We employ the Fukagata-Iwamoto-Kasagi decomposition [K. Fukagata et al., Phys. Fluids 14, 73 (2002)] and spectral analysis to study the interaction between intense adverse pressure gradient and these control strategies. We find that the control modifies skin-friction contributions differently in adverse-pressure-gradient and zero-pressure-gradient boundary layers. In particular, the control strategies modify considerably both the streamwisedevelopment and the pressure-gradient contributions, which have high magnitude when a strong adverse pressure gradient is present. Blowing and suction also impact the convection of structures in the wall-normal direction. Overall, our results suggest that it is not possible to simply separate pressure-gradient and control effects, a fact to take into account in future studies on control design in practical applications.

  • 48.
    Aulitto, Alessia
    et al.
    Eindhoven University of Technology, The Netherlands.
    Hirschberg, Avraham
    Eindhoven University of Technology, The Netherlands.
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL. Eindhoven University of Technology, The Netherlands.
    Saxena, Vertika
    Eindhoven University of Technology, The Netherlands.
    Experimental study of a slit in the presence of a bias flow under medium- and high-level acoustic excitations2023In: International Journal of Spray and Combustion Dynamics, ISSN 1756-8277, Vol. 15, no 2, p. 117-126Article in journal (Refereed)
    Abstract [en]

    This work presents an experimental investigation of the acoustic properties of a slit in the presence of a bias flow under moderate- and high-acoustic excitations. Impedance tube experiments are discussed for a geometry inspired by deep punching resulting in a cut in the plate. The acoustic transfer impedance of the plate is discussed for several bias flow velocities, acoustic excitation, and different frequencies. In the range considered for this study, a bias flow appears to have two main effects, globally enhancing the sound absorption of the plate and creating a protective layer downstream of the plate due to the interaction between the slits. A maximum of the enhancement factor is found at a specific ratio between the acoustic velocity and the bias flow velocity. Two simple asymptotic behaviors are found, dominated by the flow or by the acoustic excitation, respectively. The behavior of the inertance is complex. Globally the inertance decreases with decreasing flow Strouhal number while its dependency on the amplitude of the acoustic velocity is less obvious.

  • 49.
    Baclet, Sacha
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH Digital Futures.
    Khoshkhah, Kaveh
    ITS Lab, Institute of Computer Science, University of Tartu, Estonia.
    Pourmoradnasseri, Mozhgan
    ITS Lab, Institute of Computer Science, University of Tartu, Estonia.
    Rumpler, Romain
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL. KTH Digital Futures.
    Hadachi, Amnir
    ITS Lab, Institute of Computer Science, University of Tartu, Estonia.
    Near-real-time dynamic noise mapping and exposure assessment using calibrated microscopic traffic simulations2023In: Transportation Research Part D: Transport and Environment, ISSN 1361-9209, E-ISSN 1879-2340, Vol. 124, article id 103922Article in journal (Refereed)
    Abstract [en]

    With prospective applications ranging from improving the understanding of the daily and seasonal dynamics of noise exposure to raising public awareness of the associated health effects, dynamic noise mapping in real time is one of the next milestones in environmental acoustics. The present contribution proposes a methodology for near-real-time dynamic noise mapping, enabling the generation of dynamic noise maps and the calculation of advanced noise exposure indicators, here arbitrarily established for the previous day, on the scale of large urban areas. This methodology consists in (i) collecting live traffic counts, measured using dedicated IoT sensors, (ii) calibrating a microscopic traffic simulation using these sparsely distributed traffic counts, (iii) modelling noise emission and propagation from the microscopic traffic simulation, and finally, (iv) post-processing the noise simulation output for the calculation of a wide range of exposure indicators. The applicability of the method is demonstrated on the city of Tartu, Estonia.

  • 50.
    Baclet, Sacha
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Venkataraman, Siddharth
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Rumpler, Romain
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    A methodology to assess the impact of driving noise from individual vehicles in an urban environment2021In: "Advances in Acoustics, Noise and Vibration - 2021" Proceedings of the 27th International Congress on Sound and Vibration, ICSV 2021 / [ed] Carletti E., Crocker M., Pawelczyk M., Tuma J., 2021Conference paper (Other academic)
    Abstract [en]

    Traffic is a major source of environmental noise pollution in urban areas. The present contribution focuses on a methodology designed to assess the impact of the noise generated by individual vehicles on a city's population using NoiseModelling, an open-source library implementing the CNOSSOS-EU model, capable of producing environmental noise maps. The initial step of the proposed method consists in processing microscopic traffic data (simulated in the present contribution), where the traffic intensity is dependent on the time of day that is targeted. The micro-traffic data is subsequently used to generate background noise maps by simulating the propagation of traffic noise. Then, the impact of the noise from the vehicle of interest is simulated, based on several parameters (route followed, type of motorization: diesel or hybrid, etc.). Finally, the data is post-processed to calculate the "exceedance" (increase in ambient noise) caused by the vehicle, taking the previously calculated background noise maps as reference. The complete methodology, its underlying assumptions, and the associated criteria proposed in order to assess the impact of noise emissions from individual vehicles is demonstrated on a realistic scenario.

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