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Agrawal, V., Kulachenko, A., Scapin, N., Tammisola, O. & Brandt, L. (2024). An efficient isogeometric/finite-difference immersed boundary method for the fluid–structure interactions of slender flexible structures. Computer Methods in Applied Mechanics and Engineering, 418, Article ID 116495.
Open this publication in new window or tab >>An efficient isogeometric/finite-difference immersed boundary method for the fluid–structure interactions of slender flexible structures
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2024 (English)In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 418, article id 116495Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier BV, 2024
Keywords
Fluid–structure interactions, Geometrically exact beam model, Immersed-boundary method, Incompressible flows, Isogeometric analysis, Partitioned solvers
National Category
Computational Mathematics Applied Mechanics Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-338863 (URN)10.1016/j.cma.2023.116495 (DOI)001096820100001 ()2-s2.0-85174171313 (Scopus ID)
Note

QC 20231031

Available from: 2023-10-31 Created: 2023-10-31 Last updated: 2023-11-30Bibliographically approved
Grujić, A., Bhatnagar, A., Sardina, G. & Brandt, L. (2024). Collisions among elongated settling particles: The twofold role of turbulence. Physics of fluids, 36(1), Article ID 013319.
Open this publication in new window or tab >>Collisions among elongated settling particles: The twofold role of turbulence
2024 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 36, no 1, article id 013319Article in journal (Refereed) Published
Abstract [en]

We study the collision rates of settling spheres and elongated spheroids in homogeneous, isotropic turbulence by means of direct numerical simulations aiming to understand microscale-particle encounters in oceans and lakes. We explore a range of aspect ratios and sizes relevant to the dynamics of plankton and microplastics in water environments. The results presented here confirm that collision rates between elongated particles in a quiescent fluid are more frequent than those among spherical particles in turbulence due to oblique settling. We also demonstrate that turbulence generally enhances collisions among elongated particles as compared to those expected for a random distribution of the same particles settling in a quiescent fluid, although we also find a decrease in collision rates in turbulence for particles of the highest density and moderate aspect ratios ( A = 5 ) . The increase in the collision rate due to turbulence is found to quickly decrease with aspect ratio, reach a minimum for aspect ratios approximately equal to 5, and then slowly increase again, with an increase up to 50% for the largest aspect ratios investigated. This non-monotonic trend is explained as the result of two competing effects: the increase in the surface area with aspect ratio (beneficial to increase encounter rates) and the alignment of nearby prolate particles in turbulence (reducing the probability of collision). Turbulence mixing is, therefore, partially balanced by rod alignment at high particle aspect ratios.

Place, publisher, year, edition, pages
AIP Publishing, 2024
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:kth:diva-342840 (URN)10.1063/5.0177893 (DOI)001146263000013 ()2-s2.0-85182727118 (Scopus ID)
Note

QC 20240201

Available from: 2024-01-31 Created: 2024-01-31 Last updated: 2024-02-12Bibliographically approved
Hosen, H. F., Shahmardi, A., Brandt, L. & Solsvik, J. (2024). Dynamics of a single bubble in Newtonian and non-Newtonian fluids: Experimental and simulation approaches. International Journal of Multiphase Flow, 174, Article ID 104789.
Open this publication in new window or tab >>Dynamics of a single bubble in Newtonian and non-Newtonian fluids: Experimental and simulation approaches
2024 (English)In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 174, article id 104789Article in journal (Refereed) Published
Abstract [en]

The intricate nature of non-Newtonian fluid rheology has raised notable attention, particularly in gas–liquid systems, where the dispersed bubbles may generate shear forces and change the shear-dependent viscosity of the surrounding liquid. While the effective shear rate, γ̇eff=vb/Db, is commonly used to approximate the shear-thinning viscosity around spherical bubbles, deviations may arise for deformed bubbles present in real systems. This work combines laboratory experiments and numerical simulations to investigate the evolution of a single rising bubble in three different systems: water, glycerol/water solutions characterizing viscous-Newtonian systems, and carboxymethyl cellulose (CMC) aqueous solutions exhibiting shear-thinning. The experiment was performed with bubble sizes of 1–9mm using imaging techniques. The measured fluid rheology is modeled by the Carreau model, and used in 3D direct numerical simulations based on a diffuse interface approach. The shear-thinning behaviors are found to increase the bubble terminal velocity through two distinct mechanisms: reducing the apparent viscosity around the bubble and promoting the bubble deformation. The extent of the shear-thinning effect depends on the three dominating regimes under which different rheology parameters play a significant role. Finally, empirical models for bubble terminal velocity and drag coefficient are evaluated using two shear-thinning viscosity estimations, based on the effective shear rate and the average shear-thinning viscosity near the bubble interface. The good agreement between experimental and simulation results validates the proposed models.

Place, publisher, year, edition, pages
Elsevier BV, 2024
Keywords
Bubble hydrodynamics, Fluid rheology, Non-Newtonian, Shear-thinning, Single bubble, Terminal velocity
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-344598 (URN)10.1016/j.ijmultiphaseflow.2024.104789 (DOI)001221619100001 ()2-s2.0-85187220182 (Scopus ID)
Note

QC 20240524

Available from: 2024-03-20 Created: 2024-03-20 Last updated: 2024-05-24Bibliographically approved
Takeishi, N., Rosti, M. E., Yokoyama, N. & Brandt, L. (2024). Viscoelasticity of suspension of red blood cells under oscillatory shear flow. Physics of fluids, 36(4), Article ID 041905.
Open this publication in new window or tab >>Viscoelasticity of suspension of red blood cells under oscillatory shear flow
2024 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 36, no 4, article id 041905Article in journal (Refereed) Published
Abstract [en]

We present a numerical analysis of the rheology of a suspension of red blood cells (RBCs) for different volume fractions in a wall-bounded, effectively inertialess, small amplitude oscillatory shear (SAOS) flow for a wide range of applied frequencies. The RBCs are modeled as biconcave capsules, whose membrane is an isotropic and hyperelastic material following the Skalak constitutive law. The frequency-dependent viscoelasticity in the bulk suspension is quantified by the complex viscosity, defined by the amplitude of the particle shear stress and the phase difference between the stress and shear. SAOS flow basically impedes the deformation of individual RBCs as well as the magnitude of fluid-membrane interactions, resulting in a lower specific viscosity and first and second normal stress differences than in steady shear flow. Although it is known that the RBC deformation alone is sufficient to give rise to shear-thinning, our results show that the complex viscosity weakly depends on the frequency-modulated deformations or orientations of individual RBCs but rather depends on combinations of the frequency-dependent amplitude and phase difference. The effect of the viscosity ratio between the cytoplasm and plasma and of the capillary number is also assessed.

Place, publisher, year, edition, pages
AIP Publishing, 2024
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-345740 (URN)10.1063/5.0196272 (DOI)001197584600008 ()2-s2.0-85189455319 (Scopus ID)
Note

QC 20240419

Available from: 2024-04-18 Created: 2024-04-18 Last updated: 2024-05-13Bibliographically approved
Olad, P., Innings, F., Crialesi-Esposito, M., Brandt, L. & Hakansson, A. (2023). Comparison of turbulent drop breakup in an emulsification device and homogeneous isotropic turbulence: Insights from numerical experiments. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 657, 130569, Article ID 130569.
Open this publication in new window or tab >>Comparison of turbulent drop breakup in an emulsification device and homogeneous isotropic turbulence: Insights from numerical experiments
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2023 (English)In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 657, p. 130569-, article id 130569Article in journal (Refereed) Published
Abstract [en]

Turbulent emulsification is of considerable industrial interest. Nevertheless, numerical experiments (direct nu-merical simulations, DNS, with highly resolved interface tracking) have been mainly used to study drop breakup in idealized flows. This study, therefore, compares drop breakup in two different settings (homogenous and isotropic flow, and a simplified high-pressure homogenizer) with the intention of better understanding how insight gained from the idealized systems can be applied to industrially relevant devices. The flow differs be-tween the two cases, with highly anisotropic and inhomogeneous turbulence in the latter. Results show simi-larities between the two cases regarding morphology of breakup, suggesting that the underlying mechanism, as a function of Weber number, is similar. However, differences are also observed, e.g., in terms of breakup time and deformed morphology, which are associated with the locality of the turbulence in the homogenizer. Implications for an improved understanding of turbulent breakup in industrially relevant devices are discussed.

Place, publisher, year, edition, pages
Elsevier BV, 2023
Keywords
High-pressure homogenizer, Emulsification, Turbulence, Direct numerical simulation
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-322610 (URN)10.1016/j.colsurfa.2022.130569 (DOI)000889727400006 ()2-s2.0-85141924993 (Scopus ID)
Note

QC 20221223

Available from: 2022-12-23 Created: 2022-12-23 Last updated: 2022-12-23Bibliographically approved
Lu, M., Deng, J., Mao, X. & Brandt, L. (2023). Dynamic Buckling of a Filament Impacted by a Falling Droplet. Physical Review Letters, 131(18)
Open this publication in new window or tab >>Dynamic Buckling of a Filament Impacted by a Falling Droplet
2023 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 131, no 18Article in journal (Refereed) Published
Abstract [en]

We investigate the buckling dynamics of an elastic filament impacted axially by a falling liquid droplet, and identify the buckling modes through a combination of experimental and theoretical analyses. A phase diagram is constructed on a plane defined by two primary parameters: the falling height and the filament length. Two transition boundaries are observed, with one marking the occurrence of dynamic buckling and the other separating the buckling regime into two distinct modes. Notably, the hydrodynamic viscous force of the liquid dominates during the impact, with the dynamic buckling instability predicted by a single elastoviscous number. The critical load is twice the critical static load, which is, however, lower for the deformable droplet utilized in our study, as compared to a solid object. An additional time-dependent simulation on a longer filament exhibits a higher buckling mode, succeeded by a more distinct coarsening process than our experimental observations.

Place, publisher, year, edition, pages
American Physical Society (APS), 2023
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-344491 (URN)10.1103/PhysRevLett.131.184002 (DOI)001172714000001 ()37977627 (PubMedID)2-s2.0-85176122280 (Scopus ID)
Note

QC 20240318

Available from: 2024-03-18 Created: 2024-03-18 Last updated: 2024-03-18Bibliographically approved
Scapin, N., Demou, A. D. & Brandt, L. (2023). Evaporating Rayleigh-Benard convection: prediction of interface temperature and global heat transfer modulation. Journal of Fluid Mechanics, 957, Article ID A12.
Open this publication in new window or tab >>Evaporating Rayleigh-Benard convection: prediction of interface temperature and global heat transfer modulation
2023 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 957, article id A12Article in journal (Refereed) Published
Abstract [en]

We propose an analytical model to estimate the interface temperature Theta(Gamma) and the Nusselt number Nu for an evaporating two-layer Rayleigh-Benard configuration in statistically stationary conditions. The model is based on three assumptions: (i) the Oberbeck-Boussinesq approximation can be applied to the liquid phase, while the gas thermophysical properties are generic functions of thermodynamic pressure, local temperature and vapour composition, (ii) the Grossmann-Lohse theory for thermal convection can be applied to the liquid and gas layers separately and (iii) the vapour content in the gas can be taken as the mean value at the gas-liquid interface. We validate this setting using direct numerical simulations in a parameter space composed of the Rayleigh number (10(6) <= Ra <= 10(8)) and the temperature differential (0.05 <= epsilon <= 0.20), which modulates the variation of state variables in the gas layer. To better disentangle the variable property effects on Theta(Gamma) and Nu, simulations are performed in two conditions. First, we consider the case of uniform gas properties except for the gas density and gas-liquid diffusion coefficient. Second, we include the variation of specific heat capacity, dynamic viscosity and thermal conductivity using realistic equations of state. Irrespective of the employed setting, the proposed model agrees very well with the numerical simulations over the entire range of Ra-epsilon investigated.

Place, publisher, year, edition, pages
Cambridge University Press (CUP), 2023
Keywords
Benard convection, multiphase flow, condensation/evaporation
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-324797 (URN)10.1017/jfm.2023.57 (DOI)000933465400001 ()2-s2.0-85148487797 (Scopus ID)
Note

QC 20230316

Available from: 2023-03-16 Created: 2023-03-16 Last updated: 2023-03-16Bibliographically approved
Feneuil, B., Iqbal, K. T., Jensen, A., Brandt, L., Tammisola, O. & Carlson, A. (2023). Experimental and numerical investigation of bubble migration in shear flow: Deformability-driven chaining and repulsion. Physical Review Fluids, 8(6), Article ID 063602.
Open this publication in new window or tab >>Experimental and numerical investigation of bubble migration in shear flow: Deformability-driven chaining and repulsion
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2023 (English)In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 8, no 6, article id 063602Article in journal (Refereed) Published
Abstract [en]

We study the interaction-induced migration of bubbles in shear flow and observe that bubbles suspended in elastoviscoplastic emulsions organize into chains aligned in the flow direction, similarly to particles in viscoelastic fluids. To investigate the driving mechanism, we perform experiments and simulations on bubble pairs, using suspending fluids with different rheological properties. First, we notice that, for all fluids, the interaction type depends on the relative position of the bubbles. If they are aligned in the vorticity direction, then they repel, if not, then they attract each other. The simulations show a similar behavior in Newtonian fluids as in viscoelastic and elastoviscoplastic fluids, as long as the capillary number is sufficiently large. This shows that the interaction-related migration of the bubbles is strongly affected by the bubble deformation. We suggest that the cause of migration is the interaction between the heterogeneous pressure fields around the deformed bubbles, due to capillary pressure.

Place, publisher, year, edition, pages
American Physical Society (APS), 2023
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-332199 (URN)10.1103/PhysRevFluids.8.063602 (DOI)001019545300003 ()2-s2.0-85164008146 (Scopus ID)
Note

QC 20230721

Available from: 2023-07-21 Created: 2023-07-21 Last updated: 2023-07-21Bibliographically approved
Crialesi-Esposito, M., Scapin, N., Demou, A. D., Rosti, M. E., Costa, P., Spiga, F. & Brandt, L. (2023). FluTAS: A GPU-accelerated finite difference code for multiphase flows. Computer Physics Communications, 284, Article ID 108602.
Open this publication in new window or tab >>FluTAS: A GPU-accelerated finite difference code for multiphase flows
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2023 (English)In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 284, article id 108602Article in journal (Refereed) Published
Abstract [en]

We present the Fluid Transport Accelerated Solver, FluTAS, a scalable GPU code for multiphase flows with thermal effects. The code solves the incompressible Navier-Stokes equation for two-fluid systems, with a direct FFT-based Poisson solver for the pressure equation. The interface between the two fluids is represented with the Volume of Fluid (VoF) method, which is mass conserving and well suited for complex flows thanks to its capacity of handling topological changes. The energy equation is explicitly solved and coupled with the momentum equation through the Boussinesq approximation. The code is conceived in a modular fashion so that different numerical methods can be used independently, the existing routines can be modified, and new ones can be included in a straightforward and sustainable manner. FluTAS is written in modern Fortran and parallelized using hybrid MPI/OpenMP in the CPU-only version and accelerated with OpenACC directives in the GPU implementation. We present different benchmarks to validate the code, and two large-scale simulations of fundamental interest in turbulent multiphase flows: isothermal emulsions in HIT and two-layer Rayleigh-Bénard convection. FluTAS is distributed through a MIT license and arises from a collaborative effort of several scientists, aiming to become a flexible tool to study complex multiphase flows. Program summary: Program Title: : Fluid Transport Accelerated Solver, FluTAS. CPC Library link to program files: https://doi.org/10.17632/tp6k8wky8m.1 Developer's repository link: https://github.com/Multiphysics-Flow-Solvers/FluTAS.git. Licensing provisions: MIT License. Programming language: Fortran 90, parallelized using MPI and slab/pencil decomposition, GPU accelerated using OpenACC directives. External libraries/routines: FFTW, cuFFT. Nature of problem: FluTAS is a GPU-accelerated numerical code tailored to perform interface resolved simulations of incompressible multiphase flows, optionally with heat transfer. The code combines a standard pressure correction algorithm with an algebraic volume of fluid method, MTHINC [1]. Solution method: the code employs a second-order-finite difference discretization and solves the two-fluid Navier-Stokes equation using a projection method. It can be run both on CPU-architectures and GPU-architectures.

Place, publisher, year, edition, pages
Elsevier BV, 2023
Keywords
High-performance computing, Multiphase flows, OpenACC directives, Turbulence in multiphase flows, Volume-of-fluid method
National Category
Fluid Mechanics and Acoustics Computational Mathematics
Identifiers
urn:nbn:se:kth:diva-328851 (URN)10.1016/j.cpc.2022.108602 (DOI)001017747700001 ()2-s2.0-85142890028 (Scopus ID)
Note

QC 20230614

Available from: 2023-06-14 Created: 2023-06-14 Last updated: 2023-09-06Bibliographically approved
Crialesi-Esposito, M., Boffetta, G., Brandt, L., Chibbaro, S. & Musacchio, S. (2023). Intermittency in turbulent emulsions. Journal of Fluid Mechanics, 972, Article ID A37.
Open this publication in new window or tab >>Intermittency in turbulent emulsions
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2023 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 972, article id A37Article in journal (Refereed) Published
Abstract [en]

We investigate the statistics of turbulence in emulsions of two immiscible fluids of the same density. We compute velocity increments between points conditioned to be located in the same phase or in different phases, and examine their probability density functions (PDFs) and the associated structure functions (SFs). This enables us to demonstrate that the presence of the interface reduces the skewness of the PDF at small scales and therefore the magnitude of the energy flux towards the dissipative scales, which is quantified by the third-order SF. The analysis of the higher-order SFs shows that multiphase turbulence is more intermittent than single-phase turbulence. In particular, the local scaling exponents of the SFs display a saturation below the Kolmogorov-Hinze scale, which indicates the presence of large velocity gradients across the interface. Interestingly, the statistics of the velocity differences in the carrier phase recovers that of single-phase turbulence when the viscosity of the dispersed phase is high.

Place, publisher, year, edition, pages
Cambridge University Press (CUP), 2023
Keywords
multiphase flow, intermittency
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-339359 (URN)10.1017/jfm.2023.628 (DOI)001079232800001 ()2-s2.0-85175266691 (Scopus ID)
Note

QC 20231108

Available from: 2023-11-08 Created: 2023-11-08 Last updated: 2023-11-08Bibliographically approved
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