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. 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
  2. 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
  3. 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
  4. 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
  5. 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
  6. 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.
  7. 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
  8. 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
  9. 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
  10. 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
  11. 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
  12. 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
  13. 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
  14. 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
  15. 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
  16. 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. 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
  2. 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
  3. 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
  4. 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
  5. 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
  6. 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
  7. 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
  8. 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
  9. 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
  10. 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#
  11. 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
  12. 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
  13. 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
  14. 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
  15. A. Wachs. A DEM-DLM/FD method for direct numerical simulation of particulate flows : Sedi- mentation 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
  16. 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
  17. 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
  18. 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#