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  • 1.
    Altimira, Mireia
    et al.
    Lund University.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Effect of fuel flexibility on cavitation in injector-like flows2014In: Proceedings of the 26th ILASS-Europe 2014, 2014Conference paper (Refereed)
  • 2. Arlov, D.
    et al.
    Revstedt, J.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Numerical simulation of a gas-liquid Rushton stirred reactor - LES and LPT2008In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 37, no 7, p. 793-801Conference paper (Refereed)
    Abstract [en]

    Simulations of aerated stirred reactor is performed using a combination of large eddy simulation (LES) and Lagrangian particle tracking (LPT). A single impeller Rushton turbine is positioned at the center of the reactor and air is introduced at the bottom through a circular sparger. Effects of the gas volume flow, stirrer speed and sparger dimension are investigated. The results show that the time averaged liquid velocities in radial and tangential directions decrease with increasing gas volume fraction. In the axial direction, the gas redirects the radial jet upwards, breaking the symmetry of the ring vortices. Especially, for a narrower sparger, a more concentrated tilt upwards is observed with a larger region of negative axial velocity. Although, low aeration number is used, the periodicity from the impeller is decreasing and interfering with the creation of the trailing vortex pair. The gas dispersion increases with decreasing the sparger diameter.

  • 3.
    Bark, Fritz H.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Vynnycky, M.
    A note on electrolysis with forced convection at large peclet number in a channel and an excess of supporting electrolyte2008In: Russian journal of electrochemistry, ISSN 1023-1935, E-ISSN 1608-3342, Vol. 44, no 4, p. 470-478Article in journal (Refereed)
    Abstract [en]

    Electrolysis of an aqueous solution of a metal salt with an excess of supporting electrolyte flowing in a two-dimensional channel is considered. The reaction kinetics is modeled by a Butler - Volmer law. The metal electrodes are symmetrically flush mounted in the channel walls, which are otherwise electrically insulating. Using the perturbation scheme originally proposed by Levich for electrolytes with an excess of supporting electrolyte, a solution in closed form, involving the root of a transcendental algebraic equation, is obtained for the polarization curve. For small and large values of the potential difference between the electrodes, explicit expressions for the polarization curve and the distributions of electric current and concentration on the electrodes are obtained. Particular attention is given to the conditions prevailing during the asymptotic approach to the limiting current.

  • 4.
    Bennani, Patrick
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Development and optimazation of synthetic jets for active flow control2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 5. Borg, K. I.
    et al.
    Birgersson, K. E.
    Bark, Fritz H.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Effects of non-linear kinetics on free convection in an electrochemical cell with a porous separator2007In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 37, no 11, p. 1287-1302Article in journal (Refereed)
    Abstract [en]

    The spatial evolution of the ionic concentration of an electrolyte in an isothermal electrochemical cell with a porous separator between the electrodes was investigated for large values of Rayleigh number. The reaction kinetics were described by the Butler-Volmer equation. The full problem, involving the coupled partial differential equations describing the velocity field, the ionic concentration, and the electric potential, was reduced by means of regular and singular perturbation theory, to a simplified evolution equation, coupled with a transcendental function for the ionic concentration and electric potential; the solution was found to agree well with the numerical solution of the full problem. In the limit of large and small cell voltages, closed analytical solutions were secured for the concentration, potential, and overall current density.

  • 6.
    Brynjell-Rahkola, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Hanifi, Ardeshir
    KTH, School of Engineering Sciences (SCI), Mechanics. 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), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Modal analysis of roughness-induced crossflow vortices in a Falkner-Skan-Cooke boundary layer2013In: International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2013, TSFP-8 , 2013Conference paper (Refereed)
    Abstract [en]

    A three-dimensional global stability analysis using high-order direct numerical simulations is performed to investigate the effect of surface roughness with Reynolds number (based on roughness height) Rek above and below the critical value for transition, on the eigenmodes of a Falkner-Skan-Cooke boundary layer. The surface roughness is introduced with the immersed boundary method and the eigenvalues and eigenfunctions are solved using an iterative time-stepper method. The study reveals a global instability for the case with higher Reynolds number that causes the flow in the non-linear simulations to break down to turbulence shortly downstream of the roughness. Examination of the unstable linear global modes show that these are the same modes that are observed in experiments immediately before breakdown due to secondary instability, which emphasizes the importance of these modes in transition.

  • 7. Duwig, C.
    et al.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Large eddy simulation of a H-2/N-2 lifted flame in a vitiated co-flow2008In: Combustion Science and Technology, ISSN 0010-2202, E-ISSN 1563-521X, Vol. 180, no 3, p. 453-480Article in journal (Refereed)
    Abstract [en]

    A lifted turbulent H-2/N-2 flame in a vitiated co-flow is studied using Large Eddy Simulation together with a closure based on perfectly stirred reactors. A part of the closure, chemical look-up tables, are generated to close the filtered temperature equations and to compute local radical concentrations throughout the computational domain. The approach has been used to simulate a lifted turbulent flame. The results have been found to be insensitive to the combustion model employed and to the grid resolution. However, the results are very sensitive to the temperature of the co-flow stream and this result is well in line with previous findings. The numerical predictions were further compared to detailed experimental data obtained by Cabra et al. (2002). The agreement between the two sets of data is very good, indicating that the present approach predicts successfully the combustion process including the OH mass fractions. Finally, the LES data were used to study the flame dynamics and stabilization mechanisms.

  • 8. Duwig, C.
    et al.
    Salewski, M.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Simulations of a turbulent flow past a sudden expansion: A sensitivity analysis2008In: AIAA Journal, ISSN 0001-1452, E-ISSN 1533-385X, Vol. 46, no 2, p. 408-419Conference paper (Refereed)
    Abstract [en]

    Large eddy simulation is used to study the flow behind a pair of symmetric backward-facing steps. As reported in the literature, the flow exhibits an asymmetric pattern characterized by the deflection of the jet toward one of the walls. The large eddy simulation results are compared with laser Doppler anemometry measurements showing the ability of the present numerical tool to capture the complex features of the flow. Furthermore, a sensitivity study is conducted to assess the influence of the grid resolution, the inflow boundary, the channel width, and the step size on the flowfield. The flow was found to be only weakly sensitive to the grid, assuring the quality of the simulation results. The inflow boundary influences the mean results only marginally unless low-frequency fluctuations are applied. In this case, the flowfield recovers a mean symmetry with suppression of the jet bending. The jet mean bending has also been shown to increase with the step size h and to decrease with increasing channel width.

  • 9. Duwig, C.
    et al.
    Stankovic, D.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Li, G.
    Gutmark, E.
    Experimental and numerical study of flameless combustion in a model gas turbine combustor2008In: Combustion Science and Technology, ISSN 0010-2202, E-ISSN 1563-521X, Vol. 180, no 2, p. 279-295Article in journal (Refereed)
    Abstract [en]

    Flameless combustion is an attractive solution to address existing problems of emissions and stability when operating gas turbine combustors. Theoretical, numerical and experimental approaches were used to study the flameless gas turbine combustor. The emissions and combustion stability were measured and the limits of the flameless regime are discussed. Using experimental techniques and Large Eddy Simulation (LES), detailed knowledge of the flow field and the oxidation dynamics was obtained. In particular the relation between the turbulent coherent structures dynamics and the flameless oxidation was highlighted. A model for flameless combustion simulations including detailed chemistry was derived. The theoretical analysis of the flameless combustion provides 2 non-dimensional numbers that define the range of the flameless mode. It was determined that the mixture that is ignited and burnt is composed of similar to 50% of fresh gases and similar to 50% vitiated gases.

  • 10. Evegren, Philip
    et al.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Revstedt, Johan
    Wall shear stress variations in a 90-degree bifurcation in 3D pulsating flows2010In: Medical Engineering and Physics, ISSN 1350-4533, E-ISSN 1873-4030, Vol. 32, no 2, p. 189-202Article in journal (Refereed)
    Abstract [en]

    The exact role of fluid mechanics in the patho-physiological process of atherosclerosis has been a research topic over many years, yet without clear conclusive result. One has observed that morphological manifestations of the disease are found at some well-defined locations: certain vessel bifurcations and in curvatures. The flow in these regions is characterized by unsteadiness and often separation. Currently there are no complete theories that can explain the process since the different components in the process are not fully understood. Here we carry out detailed computations of the unsteady flow in an arterial segment typical to location of early appearance of arterial lesions. We study the wall shear stress (WSS) field variations near a junction with the purpose of identifying fluid-mechanical parameters that can be related to sites of atheroslcerosis. The results show that regions associated with atherosclerosis experience highly elevated temporal- and spatial-derivatives of the WSS, also at less commonly known locations. Thus, large derivatives in time and space do not seem unique for the most common areas of atherosclerosis. Differences in WSS character between these locations are identified as differences in the time period of back flow as well as differences in the magnitude of the WSS derivatives. The data is presented in a way that facilitates understanding of the variations in WSS.

  • 11. Gherman, B. G.
    et al.
    Malael, I.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Porumbel, I.
    Jet pump optimization through Reynolds averaged: Navier-Stokes simulation analysis2015In: 22nd AIAA Computational Fluid Dynamics Conference, American Institute of Aeronautics and Astronautics, 2015Conference paper (Refereed)
    Abstract [en]

    The paper presents the aerodynamic analysis of an air jet pump by means of Reynolds Averaged Navier-Stokes (RANS) simulations. A baseline configuration, reproducing an existing jet pump is first analysed from the perspective of overall mean compressible flow behaviour, turbulence production and mixing, and efficiency performance. Several constructive solutions are proposed in order to achieve enhanced mixing and efficiency performance. All the cases are investigated for the same operating condition of interest. As a result of the numerical analysis, two solutions are selected as potential improved constructive solutions in terms of mixing and efficiency performance. It is intended to complement the study by further experimental measurements for the baseline set-up and for the two selected configurations, in order to assess their actual performance and to validate the numerical data.

  • 12.
    Ipek, Nulifer
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Faxén Laboratory. KTH, School of Engineering Sciences (SCI), Mechanics.
    Lior, Noam
    University of Pennsylvania, Dept. Mech. Eng. and Appl. Mechanics.
    Vynnycky, Michael
    KTH, School of Engineering Sciences (SCI), Centres, Faxén Laboratory. KTH, School of Engineering Sciences (SCI), Mechanics.
    Bark, Fritz H.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Numerical and experimental study of the effect of gas evolution in electrolytic pickling2006In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 36, no 12, p. 1367-1379Article in journal (Refereed)
    Abstract [en]

    As part of a progressive approach to model the electrolytic pickling process, this paper focuses on the important aspect of hydrogen and oxygen gas evolution on the electrodes and on the steel strip being pickled. The system considered consists of type 316 stainless steel pickled in aqueous sodium sulphate, with lead anodes and stainless steel cathodes. The mathematical model is two-dimensional steady-state, and includes the differential equations describing the effect of migration, giving the potential and current fields, and the Tafel kinetic rate expressions for hydrogen and oxygen gas generation. Experiments were conducted to obtain a better understanding of the process and for model validation. Good agreement between the experimental measurements of the global current efficiency and the model predictions was obtained.

  • 13.
    Lenaers, Peter
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    A new high-order method for the simulation of incompressible wall-bounded turbulent flows2014In: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 272, p. 108-126Article in journal (Refereed)
    Abstract [en]

    A new high-order method for the accurate simulation of incompressible wall-bounded flows is presented. In the stream- and spanwise directions the discretisation is performed by standard Fourier series, while in the wall-normal direction the method combines high-order collocated compact finite differences with the influence matrix method to calculate the pressure boundary conditions that render the velocity field exactly divergence-free. The main advantage over Chebyshev collocation is that in wall-normal direction, the grid can be chosen freely and thus excessive clustering near the wall is avoided. This can be done while maintaining the high-order approximation as offered by compact finite differences. The discrete Poisson equation is solved in a novel way that avoids any full matrices and thus improves numerical efficiency. Both explicit and implicit discretisations of the viscous terms are described, with the implicit method being more complex, but also having a wider range of applications. The method is validated by simulating two-dimensional Tollmien-Schlichting waves, forced transition in turbulent channel flow, and fully turbulent channel flow at friction Reynolds number Re-tau = 395, and comparing our data with analytical and existing numerical results. In all cases, the results show excellent agreement showing that the method simulates all physical processes correctly.

  • 14.
    Lenaers, Peter
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    A new high-order method for the simulation of incompressible wall-bounded turbulent pipe flowManuscript (preprint) (Other academic)
  • 15. Maciel, Y.
    et al.
    Facciolo, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Duwig, C.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Near-field dynamics of a turbulent round jet with moderate swirl2008In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 29, no 3, p. 675-686Article in journal (Refereed)
    Abstract [en]

    The near-field characteristics of a turbulent jet with moderate swirl generated by a fully developed, axially rotating pipe flow are investigated with LDV, time-resolved stereoscopic PIV measurements, as well as with large-eddy simulations. Large-scale vortical structures in either double, triple or even quadruple-helix configuration are found at the pipe exit but rapidly break down or amalgamate after two jet diameters. Further downstream, the swirling jet is dominated by large-scale sweeping motions not present at such a scale and strength in the non-swirling case. Of special interest is the recently discovered counter-rotating core (in the mean) which develops about six jet diameters downstream the jet exit. Data for all six Reynolds stresses is reported at this position and it is argued that the counter-rotation is the result of the transport of angular momentum radially outward by the radial-azimuthal Reynolds shear stress. The mechanisms behind this transport are discussed by qualitative analysis of the time-resolved PIV and LES data and comparisons with the non-swirling case are made.

  • 16.
    Mihaescu, Mihai
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Semlitsch, Bernhard
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Gutmark, Ephraim
    University of Cincinnati.
    Assessment of Turbulence Models for Predicting Coaxial Jets relevant to Turbofan Engines2012In: Conference on Modelling Fluid Flow (CMFF'12) / [ed] Janos Vad, 2012, p. 716-723Conference paper (Refereed)
    Abstract [en]

    A numerical study is carried out for analyzing the compressible, non-isothermal flow associated with a separate-flow exhaust nozzle system with conic plug. Within the steady-state Reynolds Averaged Navier-Stokes (RANS) framework, several two-equation turbulence models among which the standard k-epsilon, the standard k-omega, and two different Shear Stress Transport (SST) k-omega formulations are evaluated. In addition, Large Eddy Simulation (LES) approach is employed for capturing the flow dynamics associated with the coaxial jet. The computational results are compared against available experimental Particle Imaging Velocimetry (PIV) flow data, in terms of time-averaged axial velocity and turbulent kinetic energy levels.

  • 17.
    Nygård, Alexander
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Altimira, Mireia
    Lund University.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Interaction between liquid pulses during intermittent injection2014In: Proceedings of the 26th ILASS-Europe 2014, 2014Conference paper (Refereed)
  • 18.
    Pouransari, Zeinab
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Vervisch, Luc
    INSA de Rouen.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    DNS analysis of wall heat transfer and combustion regimes in a turbulent nonpremixed wall-jet flameManuscript (preprint) (Other academic)
    Abstract [en]

    Understanding the heat-release effects on the wall heat transfer in turbulent reacting flows, i.e. heat transfer with or without significant density variation, is essential for a wide variety of industrial flows, especially combustion problems. The present study focuses on the wall heat transfer and the near-wall reaction characteristics. The heat-release effects on the wall heat transfer and skin friction coefficients are investigated using three-dimensional direct numerical simulations of a turbulent reacting wall-jet flow with and without heat release. Reductions in the skin-friction coefficient are observed in the exothermic case, compared to the isothermal one, and the underlying mechanism is explained. The absolute wall heat flux also increases, while the corresponding Nusselt number decreases with increasing heat release. Furthermore, the wall effects on the near-wall average burning rate are assessed. It is found that the isothermal cold wall results in an appreciable decrease of the burning rate in the exothermic cases. We observed indications that the wall increases the chances for the development of the premixed mode and its occurrence is very fast in the wall normal direction.

  • 19.
    Renberg, Ulrica
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Westin, Fredrik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). KTH, School of Industrial Engineering and Management (ITM), Centres, Centre for Internal Cumbustion Engine Research Opus, CICERO (closed 20101231).
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Study of Junctions in 1-D & 3-D Simulation for Steady and Unsteady Flow2010In: SAE technical paper series, ISSN 0148-7191, no 01-1050Article in journal (Refereed)
    Abstract [en]

    In this work a comparative study between 1-D and 3-D calculations has been performed on different junctions. The geometries are a 90° T-junction with an area ratio of unity and a 45° junction with an area ratio of 1.78 between the main pipe and the side branch. The latter case had an offset between the centerlines of the main and the branched pipe. The 3-D modeling framework uses the Reynolds Averaged Navier-Stokes (RANS) equations with the k-ε model both for the steady and the unsteady flow cases. The comparison is made both under steady and pulsating flow conditions. The aim has been to assess the 1-D/3-D differences in terms of measures for flow losses.

    There are large discrepancies between the 1-D and 3-D computed losses in junctions. The relative differences between 1-D and 3-D computed losses in isentropic power are 63 % and 175 % for the 90° and the 45 ° junctions without including the losses in downstream pipe legs. These figures are reduced to 12 % and 114 % respectively when including a straight pipe segment of one diameter downstream of the junction outlets.

    For the 90° junction at pulsating flow, the discrepancy in 1-D and 3-D computed loss is lower compared to the steady flow case if comparing only the losses in the junction, but similar to the steady discrepancy if including the downstream pipe losses. For the 45° junction, the discrepancies are much larger. The 1-D loss is near six times that of the corresponding 3-D value if comparing the losses in the junction alone, and 3 times the 3-D value if including the losses in 10 diameter of the outlet pipe.

  • 20.
    Renberg, Ulrica
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    A Comparative Study Between 1D and 3D Computational Results for Turbulent Flow in an Exhaust Manifold and in Bent Pipes2009In: SAE Technical Papers, 2009, no 01-1112Conference paper (Refereed)
    Abstract [en]

    To improve today’s 1D engine simulation techniques it is important to investigate how well complex geometries such as the manifold are modeled by these engine simulation tools and to identify the inaccuracies that can be attributed to the 1D assumption. Time resolved 1D and 3D calculations have been performed on the turbulent flow through the outer runners of an exhaust manifold of a 2 liter turbocharged SI engine passenger car

    The total pressure drop over the exhaust manifold, computed with the 1D and 3D approach, showed to differ over an exhaust pulse. This is so even though a pressure loss coefficient correction has been employed in the 1D model to account for 3D flow effects.

    The 3D flow in the two outer runners of the manifold shows the presence of secondary flow motion downstream of the first major curvature. The axial velocity profile downstream of the first turn loses its symmetry. As the flow enters the second curvature a swirling motion is formed. This secondary flow motion prevails with considerable strength at the outlet plane, where the two runners join.

    The turbulent flow through single bent pipes with different turning angle as well as a double bent pipe is also computed using both the 1D and the 3D model, the double bent pipe also for time-varying flow. The results are expressed and compared in terms of pressure losses.

    The results show that a comparison between 1D and 3D computed pressure loss through a bent geometry is only reasonable for cases where the downstream portion of the pipe after the bend is long enough. This does not hold for geometries like an engine exhaust manifold.

  • 21. Salewski, M.
    et al.
    Stankovic, D.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Mixing in circular and non-circular jets in crossflow2008In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 80, no 2, p. 255-283Article in journal (Refereed)
    Abstract [en]

    Coherent structures and mixing in the flow field of a jet in crossflow have been studied using computational (large eddy simulation) and experimental (particle image velocimetry and laser-induced fluorescence) techniques. The mean scalar fields and turbulence statistics as determined by both are compared for circular, elliptic, and square nozzles. For the latter configurations, effects of orientation are considered. The computations reveal that the distribution of a passive scalar in a cross-sectional plane can be single- or double-peaked, depending on the nozzle shape and orientation. A proper orthogonal decomposition of the transverse velocity indicates that coherent structures may be responsible for this phenomenon. Nozzles which have a single-peaked distribution have stronger modes in transverse direction. The global mixing performance is superior for these nozzle types. This is the case for the blunt square nozzle and for the elliptic nozzle with high aspect ratio. It is further demonstrated that the flow field contains large regions in which a passive scalar is transported up the mean gradient (counter-gradient transport) which implies failure of the gradient diffusion hypothesis.

  • 22. Salewski, Mirko
    et al.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Effects of aerodynamic particle interaction in turbulent non-dilute particle-laden flow2008In: Journal of turbulence, ISSN 1468-5248, E-ISSN 1468-5248, Vol. 9, no 46, p. 1-23Article in journal (Refereed)
    Abstract [en]

    Aerodynamic four-way coupling models are necessary to handle two-phase flows with a dispersed phase in regimes in which the particles are neither dilute enough to neglect particle interaction nor dense enough to bring the mixture to equilibrium. We include an aerodynamic particle interaction model within the framework of large eddy simulation together with Lagrangian particle tracking. The particle drag coefficients are corrected depending on relative positions of the particles accounting for the strongest drag correction per particle but disregarding many-particle interactions. The approach is applied to simulate monodisperse, rigid, and spherical particles injected into crossflow as an idealization of a spray jet in crossflow. A domain decomposition technique reduces the computational cost of the aerodynamic particle interaction model. It is shown that the average drag on such particles decreases by more than 40% in the dense particle region in the near-field of the jet due to the introduction of aerodynamic four-way coupling. The jet of monodisperse particles therefore penetrates further into the crossflow in this case. The strength of the counterrotating vortex pair (CVP) and turbulence levels in the flow then decrease. The impact of the stochastic particle description on the four-way coupling model is shown to be relatively small. If particles are also allowed to break up according to a wave breakup model, the particles become polydisperse. An ad hoc model for handling polydisperse particles under such conditions is suggested. In this idealized atomizing mixture, the effect of aerodynamic four-way coupling reverses: The aerodynamic particle interaction results in a stronger CVP and enhances turbulence levels.

  • 23. Sardina, Gaetano
    et al.
    Picano, Francesco
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Caballero, Rodrigo
    Continuous Growth of Droplet Size Variance due to Condensation in Turbulent Clouds2015In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 115, no 18, article id 184501Article in journal (Refereed)
    Abstract [en]

    We use a stochastic model and direct numerical simulation to study the impact of turbulence on cloud droplet growth by condensation. We show that the variance of the droplet size distribution increases in time as t(1/2), with growth rate proportional to the large-to-small turbulent scale separation and to the turbulence integral scales but independent of the mean turbulent dissipation. Direct numerical simulations confirm this result and produce realistically broad droplet size spectra over time intervals of 20 min, comparable with the time of rain formation.

  • 24.
    Sattarzadeh Shirvan, Sohrab
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Experimental study of complex pipe flow2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 25.
    Schickhofer, Lukas
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Semlitsch, Bernhard
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Numerical Flow Simulations of a Flexible Plate Attached to an Obstacle in Crossflow2016Conference paper (Refereed)
    Abstract [en]

    For biomedical applications with relevance to the human upper respiratory tract, the knowledge of the tissue behavior when exposed to a particular flow field would be desired. Moreover, there is of importance to quantify how the tissue properties affects the biomechanics of obstruction. Since in-vivo measurements are often not possible or inappropriate, this is assessed computationally and usually using simplified/idealized geometries.

    The present work is devoted to analyze a fluid-structure interaction scenario relevant to snoring and Obstructive Sleep Apnea Syndrome (OSAS). The uncertainty of the solution to the most influential parameters will be assessed, with the aim of quantifying the interplay between the most relevant parameters responsible for tissue self-excitation and obstruction dynamics. A statistical description of the behavior shall be developed. The tissue responsible for snoring in sleep apnea patients (the soft palate) is mimicked in this numerical study by a flexible thin plate anchored to an obstacle. The fluid-structure interaction problem is simulated computationally for several configurations in order to quantify the sensitivity of the investigation parameters onto the flow-field development.

  • 26.
    Semlitsch, Bernhard
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Jyothishkumar, V
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Gutmark, Ephraim
    University of Cincinnati.
    Investigation of the Surge Phenomena in a Centrifugal Compressor Using Large Eddy Simulation2013In: ASME 2013 International Mechanical Engineering Congress and Exposition: 7A: Fluids Engineering Systems and Technologies, ASME Press, 2013, p. V07AT08A053-Conference paper (Refereed)
    Abstract [en]

    The flow through a ported shroud compressor of an automobile turbocharger is simulated using Large Eddy Simulations. Generally, the compressor is subjected to work within certain range of the mass-flow conditions. Reduction of the operation mass-flow below a certain minimum limit, leads to breakdown of the complete compressor operability. Flow reversal occurs in the compressor wheel, which results in amplification of velocity and pressure fluctuations. Consequentially, large vibratory stresses are induced into the blades under off-design condition and thereby affect the blade life duration detrimentally. The aim of this study is to understand the generation of flow-structures during extreme operable conditions (surge condition) in a centrifugal compressor. The investigation of the appearing flow-structures with the surge phenomenon is essential to explore new methods that improve the stability or the flow-operating regime of the compressor. The complete 360° compressor geometry is utilized in the computational simulations. Further, the transient sliding mesh technique is applied to account for an accurate prediction of the mesh motion and thus, the geometrical interaction between the impeller and the stationary diffuser. The numerical results are compared with available experimental measurements obtained under the same operating conditions (design and near-surge condition). The rotating stall instability is predicted using FFT data analysis. Furthermore, the numerical study captures the low frequency peak characterizing the global instability of the surge condition.

  • 27.
    Semlitsch, Bernhard
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Kumar, Jyothish
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Gutmark, Ephraim
    University of Cincinnati.
    Gancedo, Matthieu
    University of Cincinnati.
    Numerical Flow Analysis of a Centrifugal Compressor with Ported and without Ported Shroud: 2014-01-16552014Conference paper (Refereed)
    Abstract [en]

    Turbochargers are commonly used in automotive engines to increase the internal combustion engine performance during off design operation conditions. When used, a most wide operation range for the turbocharger is desired, which is limited on the compressor side by the choke condition and the surge phenomenon. The ported shroud technology is used to extend the operable working range of the compressor, which permits flow disturbances that block the blade passage to escape and stream back through the shroud cavity to the compressor inlet. The impact of this technology on a speed-line at near optimal operation condition and near surge operation condition is investigated.

    A numerical study investigating the flow-field in a centrifugal compressor of an automotive turbocharger has been performed using Large Eddy Simulation. The wheel rotation is handled by the numerically expensive sliding mesh technique. In this analysis, the full compressor geometry (360 deg) is considered. Numerical solutions with and without ported shroud for a near optimal operation condition and near-surge operation condition. The flow-field of the different cases is analyzed to elucidate the functionality of the ported shroud. In agreement with previous observations, it was found that the ported shroud reduces the flow disturbances in the blade passage for all operating conditions. However, the compressor efficiency for the off-design operation condition was found to be higher without the ported shroud, supporting the findings reported recently by an experimental investigation. The computational results are validated with experimental measurements in terms of the performance parameters and available Particle Image Velocimetry data.

  • 28.
    Semlitsch, Bernhard
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Laurendeau, E.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Steady-state and unsteady simulations of a high velocity jet into a venturi shaped pipe2014In: American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM, 2014, Vol. 1CConference paper (Refereed)
    Abstract [en]

    A jet pump consists mainly of a convergent-divergent Ven-turi shaped duct where a primary stream is applied with the role of entraining a secondary jet. Due to their simple and reliable concept, jet pumps are used in miscellaneous applications. Performance optimization of a jet pump has to be performed for various operation conditions. Thus, numerically robust and cheap models, able to predict accurately the performance parameters of such devices are necessary. Reynolds Averaged Navier-Stokes based formulations are computationally efficient to predict the performance of a jet pump. However, these simulations rely on turbulence closure coefficients, which need to be validated with experimental observations. Large Eddy Simulation solves the most energetic structures in the flow field and it can be used to capture the flow dynamics. On the experimental side, confined geometries challenge the investigation capabilities to capture the flow field accurately and in all the details. The flow field in the jet pump is investigated using Large Eddy Simulation approach and a steady state Reynolds Averaged Navier-Stokes formulation. The flow field solutions obtained with the two numerical tools are compared. A reasonable agreement for the velocity and pressure contours could be achieved. However, the turbulence kinetic energy distribution and the entrained mass flow rate are predicted to be distinct. The difference in entrained mass flow rate leads to differences in jet pump efficiency estimation.

  • 29.
    Semlitsch, Bernhard
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Influence of the jet location in supersonic crossflow disposed in a C-D duct2013In: Proceedings of the 26th Nordic Seminar on Computational Mechanics / [ed] Anders Logg, Kent-Andre Mardal, Andre ́ Massing, Oslo, 2013, p. 20-23Conference paper (Refereed)
    Abstract [en]

    The influence of shear-layer jet interaction on the flow structure generation with multiple jets in supersonic crossflow is investigated by Large Eddy Simulations (LES). A duct geometry is investigated,where the supersonic crossflow evolves in a rather sharp transition between the straight convergent and divergent section and therefore shocks establish. The jet origin location in the divergent section of the duct relative to the narrowest cross-section is significant for the shock pattern structure and the interaction point between the established separation bubble and the jets. The interaction of the separation bubble and the jets plays an important role for the flow structure generation by the jets.

  • 30.
    Semlitsch, Bernhard
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Large Eddy Simulation of Fluidic Injection into a Supersonic Convergent-Divergent Duct2015In: DLES-9, Springer, 2015Conference paper (Refereed)
  • 31.
    Semlitsch, Bernhard
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Gutmark, Ephraim
    University of Cincinnati.
    Numerical Investigation of Fluidic Control on Supersonic Jet of a Gas Turbine Engine2012In: 20th International Shock Interaction Symposium (ISIS 20) / [ed] Nicholas Apazidis, ISIS, KTH , 2012, p. 161-164Conference paper (Refereed)
    Abstract [en]

    Use of fluidics on the supersonic flow exhausting a gas turbine engine is investigated. The purpose is to control the shock-waves i.e., their location and strength by using injection tubes disposed on the circumference of the nozzle. A parametric study has been performed for quantifying the effect on shock patterns of different parameters such the nozzle pressure ratio, the injection pressure ratio, location and inclination of the tubes. Different cases have been screened, using the steady-state Reynolds-averaged Navier-Stokes formulation. For the Baseline case (without injection) at the design conditions, a grid convergence study was performed and the results were compared with experimental Particle Imaging Velocimetry data. An overall fair agreement was found. In contrast with the Baseline, significant changes in shear-layer shape, mixing, and turbulence intensity are associated with vortical structures generated due to fluidic injection. With an appropriate choice of injection parameters the ability to shift or move shocks and reduce shock strength is proven. Improvement in terms of better mixing, better thrust performance, and the possibility of reducing acoustic radiation can be shown for some of the cases.

  • 32.
    Semlitsch, Bernhard
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Gutmark, Ephraim
    University of Cincinnati.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Flow Structure Generation by Multiple Jets in Supersonic Cross-Flow2013In: 4th International Conference on Jets, Wakes and Separated Flows, ICJWSF2013, 2013Conference paper (Refereed)
    Abstract [en]

    The flow structure generation by multiple jets impinging a supersonic crossflow in the divergent section of a Convergent-Divergent (C-D) duct is investigated using compressible Large Eddy Simulations (LES). The supersonic flow-field in the C-D duct is mainly characterized by the evolving shock-structure. The effect of increasing the compressible jet to crossflow velocity ratio R to the generation of flow structures and the ability to modify the shock-pattern in the duct was studied. Traversing R, the shock-pattern can be significantly altered. This paper demonstrates that for close located jets in crossflow the vortical structures generated by the jets can interact and give rise to vortical structures in the interspace plane between the jets. The spectra for different probes are shown illustrating the characteristic flow frequencies. For all simulated cases the spectra show peaks for a defined Strouhal-number of 0.5. The jets choke in the crossflow above an R of about 0.65, which results in a faster disruption of the coherent flow structures induced by the jets. The flow field is analyzed using Proper Orthogonal Decomposition (POD).

  • 33.
    Semlitsch, Bernhard
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Wang, Yue
    Northwestern Polytechnical University.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Flow effects due to valve and piston motion in an internal combustion engine exhaust port2015In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 96, p. 18-30Article in journal (Refereed)
    Abstract [en]

    Performance optimization regarding e.g. exhaust valve strategies in an internal combustion engine is often performed based on one-dimensional simulation investigation. Commonly, a discharge coefficient is used to describe the flow behavior in complex geometries, such as the exhaust port. This discharge coefficient for an exhaust port is obtained by laboratory experiments at fixed valve lifts, room tem- peratures, and low total pressure drops. The present study investigates the consequences of the valve and piston motion onto the energy losses and the discharge coefficient. Therefore, Large Eddy Simulations are performed in a realistic internal combustion geometry using three different modeling strategies, i.e. fixed valve lift and fixed piston, moving piston and fixed valve lift, and moving piston and moving valve, to estimate the energy losses. The differences in the flow field development with the different modeling approaches is delineated and the dynamic effects onto the primary quantities, e.g. discharge coefficient, are quantified. Considering the motion of piston and valves leads to negative total pressure losses during the exhaust cycle, which cannot be observed at fixed valve lifts. Additionally, the induced flow structures develop differently when valve motion is taken into consideration, which leads to a significant disparity of mass flow rates evolving through the two individual valve ports. However, accounting for piston motion and limited valve motion, leads to a minor discharge coefficient alteration of about one to two percent. 

  • 34.
    Sundström, Elias
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Semlitsch, Bernhard
    KTH, School of Engineering Sciences (SCI).
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Assessment of the 3D Flow in a Centrifugal compressor using Steady-State and Unsteady Flow Solvers2014In: SAE Technical Paper, 2014-01-2856, 2014, SAE International , 2014Conference paper (Refereed)
    Abstract [en]

    Numerical analysis methods are used to investigate the flow in a ported-shroud centrifugal compressor under different operating conditions, i.e. several mass flow rates at two different speed lines. A production turbocharger compressor is considered, which is widely used in the heavy automotive sector. Flow solutions obtained under steady-state and transient flow assumptions are compared with available experimental data.

    The steady-state Reynolds Averaged Navier-Stokes method is used to assess the overall time averaged flow and the global performance parameters. Additionally, the Large Eddy Simulation (LES) approach is employed to capture the transient flow features and the developed flow instabilities at low mass flow rates near the surge line.

    The aim of this study is to provide new insights on the flow instability phenomena in the compressor flow near surge. Comparison of flow solutions obtained for near-optimal efficiency and near-surge conditions are carried out. The unsteady features of the flow field are quantified by means of Fourier transformation analysis, Proper Orthogonal Decomposition and Dynamic Mode Decomposition. For a near optimal efficiency set-up the frequency spectra are broad- banded with no distinct instabilities. Close to the surge line, the spectra show a distinct surge cycle frequency, which is due to flow pulsation in the compressor.

    The modal flow decomposition elucidates a mode occurring at the surge frequency. The mode explains the oscillating pumping effect occurring during surge. The surface spectra contours reveal the shape of the pressure pulsation during surge and support that a pressure gradient occurs with the oscillating modes found with the modal decomposition. 

  • 35.
    Sundström, Elias
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. 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).
    Semlitsch, Bernhard
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. 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).
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. 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).
    Similarities and differences concerning flow characteristics in centrifugal compressors of different size2016Conference paper (Refereed)
    Abstract [en]

    The appropriate choice of an automotive turbocharger compressor for an internal combustion engine is based on the compressor performance, which is commonly specified on a compressor map for different operating conditions. A wide operating range for the compressor covering all possible engine working conditions is desired. However, the application range of the compressor is limited. Different compressor designs are used to fit specific engine requirements. Naturally, these will have rather different characteristic compressor maps. The aim of the present investigation is to explain the differences in the compressor maps by analyzing the compressible flow-fields in two compressor designs from the same manufacturer, intended for a light-duty vehicle (passenger car). The flow-fields are assessed by steady-state Reynolds Averaged Navier-Stokes (RANS) simulations for several operating conditions. Similar flow features are observed near optimal efficiency operating conditions when the flow-field parameters are scaled properly. This study exposes the reason for the different measured operating ranges of the two compressors when ran at the same speed lines.

  • 36. Söder, M.
    et al.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Lindgren, B.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Effect of Swirl/Tumble (Tilt) Angle on Flow Homogeneity, Turbulence and Mixing Properties2014In: SAE technical paper series, ISSN 0148-7191, Vol. 2014-OctoberArticle in journal (Refereed)
    Abstract [en]

    In this work, the effect of swirl to tumble ratio on homogeneity, turbulence and mixing in a generic heavy duty Diesel engine during compression, is investigated using Large-Eddy Simulations. The main conclusion is that the relative importance of dilatation (relative volume change) increases whereas the effect of tumble breakdown decreases with the swirl to tumble ratio. In detail, we show that an increase in tumble raises the peak turbulence level and shifts the peak to earlier crank angles, which in turn leads to higher dissipation. Moreover, maximum turbulence level at top dead center is obtained for a combination of swirl and tumble rather than for pure tumble. Furthermore, it is observed that the peak turbulent kinetic energy displays levels three times greater than the initial kinetic energy of the tumble motion. Thus, energy is added to the flow (turbulence) by the piston through generation of vorticity by vorticity-dilatation interaction. Also, the intermediate swirl/tumble ratios are found to introduce large non-uniformity in the flow field, leading to a non-solid body like rotation. Swirl/tumble (tilt) angles larger than 19°are necessary for complete mixing of the gas within the engine cylinder. Taken together, the combined effect of a combination of swirl and tumble turbulence during compression is investigated. This knowledge is important both for engine development as well as more theoretical aspects regarding the breakdown of large scale structures in an engine.

1 - 36 of 36
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