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The 19 March 2021 at 10h00

PhD defense of Florian RENARD – “Hybrid Lattice Boltzmann Method for Compressible Flows”

Marie LABADENS |  Cerfacs Toulouse, administration room, visioconference |  


In recent years, computational fluid dynamic (CFD) methods have become essential for the aeronautics industry. These methods are used in conjunction with experimental approaches. They allow, for example, to have a precise understanding of a flow in order to help the design of aircraft components. Thus, these methods are constantly being improved to accurately reproduce the physics of simulated flows. Thanks to its reduced computational cost, its ease of implementation and use, the lattice Boltzmann method (LBM) has gradually emerged as an alternative approach to traditional numerical methods. In addition to its efficiency, this method has the advantages of being inherently unsteady and is perfectly adapted to complex geometries. Unfortunately, in its standard form, it remains limited to the simulation of isothermal and weakly compressible flows, which excludes many aeronautical applications. Nevertheless, compressible versions of this method do exist. Among the most promising ones, one can find the Hybrid method (HLBM) which uses the LBM to compute the mass and momentum equations and a finite difference scheme to computed the energy equation. This thesis focuses on the development and study of hybrid methods for the simulation of compressible flows. First, the standard LBM and its limitations are presented as well as an exhaustive bibliographical study of its compressible versions. Then, the components and general functioning of the hybrid method are shown. A simple model is developed under the Boussinesq approximation and successfully tested. However, its naive extension to the compressible equations is found to be numerically unstable due to: (1) the perfect gas coupling, and (2) the unstable nature of the LBM at high Mach numbers. These two problems are then solved by adopting a more robust collision operator for the LBM part and an entropy equation for the energy part. A stable compressible hybrid model, based on a standard D2Q9 discrete velocity lattice, is thus obtained and validated on subsonic and supersonic test cases including shock waves. Nevertheless, for the simulation of strong shock waves, the model shows conservativity problems. These are mainly attributed to the use of the entropy equation which is non-conservative. Solutions are then proposed. Then, the stability and spectral properties of HLBM schemes are studied using the von Neumann approach. This study highlights the effect of numerous parameters on numerical stability such as the collision model, the choice of the energy equation or the influence of numerical parameters like the CFL number. Instability mechanisms and stabilization methods are shown, confirming at the same time the gain in terms of stability of models based on an entropy equation. Moreover, thanks to a more in-depth analysis, this study allows to explain the observed non-physical behavior of certain models and attributes them to mode transfers.   Finally, the hybrid method is implemented in the ProLB industrial LBM solver. It is then tested on subsonic and supersonic three-dimensional compressible test cases containing boundary conditions and mesh refinements.

Keywords: LBM, compressible, hybrid, von Neumann analysis

Jonas LATTUniversité de Genève (Switzeland)Referee
Paola CINNELLASorbonne Université (France)Referee
Rémi ABGRALLUniversité de Zurich (Suisse)Member
Alois SENGISSENAirbus Toulouse (France)Invited member
Romain PAINSafran Tech (France)Invited member
Pierre SAGAUTAix-Marseille Université (France)Advisor
Jean-François BOUSSUGECERFACS Toulouse (France)Co-advisor


The AVBP code from CERFACS at the heart of three PRACE projects from the 23rd call

CERFACS |  30 September 2021

Cerfacs is involved in three PRACE projects of the 23rd call for which hour allocation runs from 01/10/2021 to 30/09/2022. Researchers from ECL/LMFA UMR5509 (Ecole Centrale de Lyon) and IMFT (UMR 5502) laboratories have earned projects entirely based on the use of the LES solver developed by Cerfacs AVBP and involve the support of experts from the CFD and COOP teams underling the importance and effectiveness of collaborations between French labs and Cerfacs. Alexis Giauque from ECL/LMFA UMR5509 (Ecole Centrale de Lyon) has obtained not only one but two PRACE projects! The first project LESFAN (RA0101, 30 000 000 CPU hours on Irene/Rome TGCC) is based on the use of AVBP in the turbomachinery version to study the generation of noise by a fan of a real airplane engine. The second, PRACE-EDGES (RA0101, 40 000 000 CPU hours on Irene/Rome TGCC) focuses on LES modeling of dens gas in complex geometries. To do so, the LMFA Team has developed advanced thermodynamic closures in AVBP allowing the direct simulation of such flows. Laurent Selle from IMFT (UMR 5502) has received CPU hours for the GASTON project (RA0061, 30 000 000 CPU hours on Marenostrum BSC) which aims to study the structure of hydrogen flames in porous materials. For this, IMFT and Cerfacs will perform coupled simulations considering the reactive flow with AVBP as well as the conduction in the porous medium with AVTP which is known to play an central role in the flame stabilization process.Read more

watch the online contest ”my thesis in 180 sec” organized for Marie Curie actions

CERFACS |  24 September 2021

Next Thursday, Sept 30th the #FallingWallsLab #MSCA research presentation competition will take place, . This is a competition in which 15 researchers compete to deliver the best presentation of their research topic in the format "my thesis in 180 seconds" . Javier Crespo-Anadon, 3rd year PhD student in the CFD team is one of the 15 finalists and he will present this thesis topic: ignition in spinning combustion engines for a reduction in CO2 emissions! You can watch it online on the above website on Sept 30th at 3pm. I encourage you to go to the website and register!  You'll be able to listen to the other participants' pitches and vote for your favorite. Come and see for yourself what kind of research the EU funds!Read more