RESEARCH INTERESTS

Our research activities pertain to the numerical simulation of complex fluid flows with heat and mass transfer, mostly laminar or inertial (weakly turbulent at most). Applications range from industrial processes in the energy industry (fluidized beds, solid particle solar receivers, slurry transport) to geophysical and environmental flows (sediment transport in rivers, landslides). The three main components of our research are:


Non-Newtonian Fluid Mechanics
The focus is on viscoplastic materials and the way they flow. My group develops and extends existing numerical methods to simulate yield stress fluid flows in assorted conditions (heat transfer, liquid/liquid interface, solid particles).


Restart flow map for Bn=0.55
Restart of a weakly compressible flow of a viscoplastic and thixotropic fluid: application to the restart of a pipeline filled with a gelled waxy crude oil


Thermal plumes in a viscoplastic fluid


A solid rectangle settling in a viscoplastic fluid returning back to rest in a finite time as a result of an increase of the Bingham number beyond the critical stability limit


Publications
  1. J. MacKenzie, E. Siren, M. Daneshi, R. Melnick, T. Treskatis, A. Wachs, J.N. Kizhakkedathu, D.M. Martinez. Fibre-reinforced biocompatible hydrogel to replace single-use plastic tubing in the clinical setting, Chemical Engineering Journal, 428, 131786, 2021. https://doi.org/10.1016/j.cej.2021.131786
  2. T. Treskatis, A. Roustaei, I. Frigaard, A. Wachs. Practical guidelines for fast, efficient and robust simulations of yield-stress flows without regularisation: A study of accelerated proximal gradient and augmented Lagrangian methods. Journal of Non-Newtonian Fluid Mechanics, 262:149-164, 2018. https://doi.org/10.1016/j.jnnfm.2018.05.002
  3. E. Chaparian, A. Wachs and I. Frigaard. Inline motion and hydrodynamic interaction of 2D particles in a viscoplastic fluid. Physics of Fluids, 30, 033101, 2018. https://doi.org/10.1063/1.5022109
  4. P. Saramito and A. Wachs. Progress in numerical simulation of yield stress fluid flows. Rheologica Acta, 56(3):211-230, 2017. http://dx.doi.org/10.1007/s00397-016-0985-9
  5. A. Wachs and I. Frigaard. Particle settling in yield stress fluids: Limiting time, distance and applications. Journal of Non-Newtonian Fluid Mechanics, 238:189-204, 2016. http://dx.doi.org/10.1016/j.jnnfm.2016.09.002
  6. I. Karimfazli, I. Frigaard and A. Wachs. Thermal plumes in viscoplastic fluids: flow onset and development. Journal of Fluid Mechanics, 787:474-507, 2016. http://dx.doi.org/10.1017/jfm.2015.639
  7. I. Karimfazli, I. Frigaard and A. Wachs. A novel heat transfer switch using the yield stress. Journal of Fluid Mechanics, 783:526-566, 2015. http://dx.doi.org/10.1017/jfm.2015.511
  8. Book chapter. R. Glowinski and A. Wachs. Numerical Methods for Non-Newtonian Fluids, Volume 16: Special Volume (Handbook of Numerical Analysis), volume XVI, chapter On the numerical simulation of viscoplastic fluid flow, pages 483-718. North-Holland, Amsterdam, 2011.
  9. A. Wachs, G. Vinay and I. Frigaard. A 1.5 D numerical model for the start up of weakly compressible flow of a viscoplastic and thixotropic fluid in pipelines. Journal of Non-Newtonian Fluid Mechanics, 159(1-3):81-94, 2009. http://dx.doi.org/10.1016/j.jnnfm.2009.02.002
  10. Z. Yu and A. Wachs. A fictitious domain method for dynamic simulation of particle sedimentation in Bingham fluids. Journal of Non-Newtonian Fluid Mechanics, 145(2- 3):78-91, 2007. http://dx.doi.org/10.1016/j.jnnfm.2007.02.007
  11. I. Frigaard, G. Vinay and A. Wachs. Compressible displacement of waxy crude oils in long pipeline startup flows. Journal of Non-Newtonian Fluid Mechanics, 147(1-2):45-64, 2007. http://dx.doi.org/10.1016/j.jnnfm.2007.07.002
  12. G. Vinay, A. Wachs and I. Frigaard. Start-up transients and efficient computation of isothermal waxy crude oil flows. Journal of Non-Newtonian Fluid Mechanics, 143(2-3):141-156, 2007. http://dx.doi.org/10.1016/j.jnnfm.2007.02.008
  13. A. Wachs. Numerical simulation of steady Bingham flow through an eccentric annular cross-section by distributed Lagrange multiplier/fictitious domain and augmented Lagrangian methods. Journal of Non-Newtonian Fluid Mechanics, 142(1-3):183-198, 2007. http://dx.doi.org/10.1016/j.jnnfm.2006.08.009
  14. G. Vinay, A. Wachs and J.F. Agassant. Numerical simulation of weakly compressible Bingham flows : The restart of pipeline flows of waxy crude oils. Journal of Non-Newtonian Fluid Mechanics, 136(2-3):93-105, 2006. http://dx.doi.org/10.1016/j.jnnfm.2006.03.003
  15. G. Vinay, A. Wachs and J.F. Agassant. Numerical simulation of non-isothermal viscoplastic waxy crude oil flows. Journal of Non-Newtonian Fluid Mechanics, 128(2-3):144-162, 2005. http://dx.doi.org/10.1016/j.jnnfm.2005.04.005
  16. A. Wachs, J.R. Clermont, and A. Khalifeh. Computations of non-isothermal viscous and viscoelastic flows in abrupt contractions using a finite volume method. Engineering Computations, 19(8):874-901, 2002. http://dx.doi.org/10.1108/02644400210450332
  17. A. Wachs and J.R. Clermont. Non-isothermal viscoelastic flow computations in an axisymmetric contraction at high Weissenberg numbers by a finite volume method. Journal of Non-Newtonian Fluid Mechanics, 95(2-3):147-184, 2000. http://dx.doi.org/10.1016/S0377-0257(00)00176-2
  18. A. Wachs, J.R. Clermont and M. Normandin. Fully-developed flow and temperature calculations for rheologically complex materials using a mapped circular domain. Engineering Computations, 16:807-830, 1999. http://dx.doi.org/10.1108/02644409910298138


Multiphase Flows
And primarily particle-laden flows. My group develops and integrates its own simulation tools in a multi-scale approach.


Packing particles on various shapes, including non-spherical, angular and non-convex shapes, in a small cylindrical reactor



Granular column collapse: dam break with 1,600,000 regular icosahedral particles



Spiralling motion of a regular tetrahedron settling in a Newtonian fluid at Re=139



190 spheres settling in a tri-periodic box at Re=148 and φ=0.1



Gad/solid fluidization of 2,000 spheres at 2 times the minimal fluidization velocity. Solid/gas density ratio is 85, Re is 29 and Fr is 0.49


Publications
  1. F. Euzenat, A. Hammouti, E. Climent, P. Fede and A. Wachs. Effect of spatial filter features on local heat transfer coefficients obtained from particle-resolved simulations of a flow through a fixed random array of rigid spherical particles, International Journal of Heat and Fluid Flow, 92, 108873, 2021.. https://doi.org/10.1016/j.ijheatfluidflow.2021.108873
  2. D. Huet, M. Jalaal, R. van Beek, D. van der Meer and A. Wachs. Granular avalanches of entangled rigid particles, Physical Review Fluids, 6, 104304, 2021. https://doi.org/10.1103/PhysRevFluids.6.104304
  3. C. Beaulieu, D. Vidal, C. Mitonkuru, A. Wachs, J. Chaouki and F. Bertrand. Effect of particle an- gularity on flow regime transitions and segregation of bidisperse blends in a rotating drum, available online, Computational Particle Mechanics, 2021. https://link.springer.com/article/10.1007/s40571-021-00421-1
  4. C. Selcuk, A. Ghigo, S. Popinet and A. Wachs. A fictitious domain method with distributed La- grange multipliers on adaptive quad/octrees for the direct numerical simulation of particle-laden flows, Journal of Computational Physics, 430, 109954, 2021. https://doi.org/10.1016/j.jcp.2020.109954
  5. A. Seyed-Ahmadi and A. Wachs. Sedimentation of inertial monodisperse suspensions of cubes and spheres, Physical Review Fluids, 6, 044306, 2021. https://doi.org/10.1103/PhysRevFluids.6.044306
  6. A. Seyed-Ahmadi and A. Wachs. Microstructure-informed probabilistic point-particle model for hydrodynamic forces and torques in particle-laden flows, Journal of Fluid Mechanics, 900, A21-1-38, 2020. https://doi.org/10.1017/jfm.2020.453
  7. M. Sulaiman, E. Climent, A. Wachs and A. Hammouti. Numerical simulations and modelling of mass transfer through random assemblies of catalyst particles: From dilute to dense reactive particulate regime, Chemical Engineering Science, 223, 115659, 2020. https://doi.org/10.1016/j.ces.2020.115659
  8. A. Seyed-Ahmadi and A. Wachs. Dynamics and wakes of freely settling and rising cubes. Physical Review Fluids, 4, 074304, 2019. https://doi.org/10.1103/PhysRevFluids.4.074304
  9. J.L. Pierson, A. Hammouti, F. Auguste and A. Wachs. Inertial flow past a finite-length axisymmetric cylinder of aspect ratio 3: Effect of the yaw angle. Physical Review Fluids, 4, 044802, 2019. https://doi.org/10.1103/PhysRevFluids.4.044802
  10. A. Wachs. Particle-scale computational approaches to model dry and saturated granular flows of non-Brownian, non-cohesive and non-spherical rigid bodies, Acta Mechanica, 230, 1919-1980, 2019. https://link.springer.com/article/10.1007/s00707-019-02389-9
  11. M. Sulaiman, A. Hammouti, E. Climent and A. Wachs. Coupling the fictitious domain and sharp interface methods for the simulation of convective mass transfer around reactive particles: Towards a reactive Sherwood number correlation for dilute systems. Chemical Engineering Science, 198, 334-351, 2019. https://doi.org/10.1016/j.ces.2019.01.004
  12. M. Sulaiman, E. Climent, A. Hammouti and A. Wachs. Mass transfer towards a reactive particle in a fluid flow : numerical simulations and modeling. Chemical Engineering Science, 199, 496-507, 2019. https://doi.org/10.1016/j.ces.2018.12.051
  13. M. Rolland, A.D. Rakotonirina, A. Devouassoux, J. Barrios Goicetty, J.Y. Delenne and A. Wachs. Predicting average void fraction and void fraction uncertainty in fixed beds of poly-lobed particles. Industrial & Engineering C hemistry Research, 58, 3902-3 911, 2019. https://doi.org/10.1021/acs.iecr.8b05557
  14. M. Rahmani, A. Hammouti and A. Wachs. Momentum balance and stresses in a suspension of spherical particles in a plane Couette flow. Physics of Fluids, 30, 043301, 2018. https://doi.org/10.1063/1.5010989
  15. A.D. Rakotonirina, J.-Y. Delenne, F. Radjai, A. Wachs. Grains3D, a flexible DEM approach for particles of arbitrary convex shape - Part III: extension to non-convex particles modelled as glued convex particles. Computational Particle Mechanics, 6, 55-84, 2019. https://doi.org/10.1007/s40571-018-0198-3
  16. A. Esteghamatian, F. Euzenat, M. Lance, A. Hammouti and A. Wachs. A stochastic formulation for the drag force based on multiscale numerical simulation of fluidized beds. International Journal of Multiphase Flow, 99:363-382, 2018. https://doi.org/10.1016/j.ijmultiphaseflow.2017.11.003
  17. A. Esteghamatian, M. Lance, A. Hammouti and A. Wachs. Particle resolved simulations of liquid/solid and gas/solid fluidized beds. Physics of Fluids, 29, 033302, 2017. http://dx.doi.org/10.1063/1.4979137
  18. A. Esteghamatian, M. Bernard, M. Lance, A. Hammouti and A. Wachs. Micro/meso simulation of a fluidized bed in a homogeneous bubbling regime, International Journal of Multiphase Flow, 92:93-111, 2017. https://doi.org/10.1016/j.ijmultiphaseflow.2017.03.002
  19. M. Bernard, E. Climent and A. Wachs. Controlling the Quality of Two-Way Euler/ Lagrange Numerical Modeling of Bubbling and Spouted Fluidized Beds Dynamics. Industrial & Engineering Chemistry Research, 56(1):368-386, 2017. http://dx.doi.org/10.1021/acs.iecr.6b03627
  20. A. Wachs, A. Hammouti, G. Vinay and M. Rahmani. Accuracy of Finite Volume/Staggered Grid Distributed Lagrange Multiplier/Fictitious Domain simulations of particulate flows. Computers & Fluids, 115:154-172, 2015. http://dx.doi.org/10.1016/j.compfluid.2015.04.006
  21. F. Dorai, C. Moura Teixeira, M. Rolland, E. Climent, M. Marcoux and A. Wachs. Fully-resolved simulations of the flow through a packed bed of cylinders : effects of size distribution. Chemical Engineering Science, 129:180-192, 2014. http://dx.doi.org/10.1016/j.ces.2015.01.070
  22. M. Rahmani and A. Wachs. Free falling and rising of spherical and angular particles. Physics of Fluids, 26:083301, 2014. http://dx.doi.org/10.1063/1.4892840
  23. L. Girolami, A. Wachs and G. Vinay. Unchannelized dam-break flows : Effects of the lateral spread- ing on the flow dynamics. Physics of Fluids, 25:043306, 2013. http://dx.doi.org/10.1063/1.4799129
  24. L. Girolami, V. Hergault, G. Vinay and A. Wachs. A three-dimensional discrete-grain model for the simulation of dam-break rectangular collapses : comparison between numerical results and experi- ments. Granular Matter, 14(3):381-392, 2012. http://link.springer.com/article/10.1007%2Fs10035-012-0342-3?LI=true#
  25. A. Wachs, L. Girolami, G. Vinay and G. Ferrer. Grains3D, a flexible DEM approach for particles of arbitrary convex shape - Part I : numerical model and validations. Powder Technology, 224:374-389, 2012. http://dx.doi.org/10.1016/j.powtec.2012.03.023
  26. V. Topin, F. Dubois, Y. Monerie, F. Perales and A. Wachs. Micro-rheology of dense particulate flows : application to immersed avalanches. Journal of Non-Newtonian Fluid Mechanics, 166(1):63-72, 2011. http://dx.doi.org/10.1016/j.jnnfm.2010.10.006
  27. A. Wachs. Rising of 3D catalyst particles in a natural convection dominated flow by a parallel DNS method. Computers & Chemical Engineering, 35(11):2169-2185, 2011. http://dx.doi.org/10.1016/j.compchemeng.2011.02.013
  28. C. Dan and A. Wachs. Direct numerical simulation of particulate flow with heat transfer. Interna- tional Journal of Heat and Fluid Flow, 31:1050-1057, 2010. http://dx.doi.org/10.1016/j.ijheatfluidflow.2010.07.007
  29. A. Wachs. A DEM-DLM/FD method for direct numerical simulation of particulate flows : Sedimentation of polygonal isometric particles in a Newtonian fluid with collisions. Computers & Fluids, 38(8):1608-1628, 2009. http://dx.doi.org/10.1016/j.compfluid.2009.01.005
  30. Z. Yu, X. Shao and A. Wachs. A fictitious domain method for particulate flows with heat transfer. Journal of Computational Physics, 217(2):424-452, 2006. http://dx.doi.org/10.1016/j.jcp.2006.01.016
  31. Z. Yu, X. Shao and A. Wachs. A fictitious domain method for particulate flows. Journal of Hydrodynamics, Ser. B, 18(3):482-486, 2006. http://dx.doi.org/10.1016/S1001-6058(06)60098-X
  32. Z. Yu, A. Wachs and Y. Peysson. Numerical simulation of particle sedimentation in shear-thinning fluids with a fictitious domain method. Journal of Non-Newtonian Fluid Mechanics, 136(2-3):126- 139, 2006. http://dx.doi.org/10.1016/j.jnnfm.2006.03.015


High Performance Computing
Most of our simulations are extremely resource-intensive. Our simulation tools are fully parallel and run on big supercomputers. Improving the scalability of my codes and designing faster algorithms is a strong component of our work.


Large scale computing with a meso scale DEM-CFD model of a gas/solid fluidized bed with 19,200,000 spheres at 3 times the minimal fluidization velocity. Solid/gas density ratio is 2083, Re is 79 and Fr is 0.007. Weak scalability of the DEM granular solver from 16 cores/4,800,000 particles to 768 cores/230,400,000 particles.


Publications
  1. A.D. Rakotonirina and A. Wachs. Grains3D, a flexible DEM approach for particles of arbitrary convex shape - Part II: parallel implementation and scalable performances. Powder Technology, 324, 18-35, 2018. https://doi.org/10.1016/j.powtec.2017.10.033
  2. A. Wachs. PeliGRIFF, a parallel DEM-DLM/FD direct numerical simulation tool for 3D particulate flows. Journal of Engineering Mathematics, 71(1):1-25, 2010. http://link.springer.com/article/10.1007%2Fs10665-010-9436-2?LI=true#