Extreme CFD workshop - User contributions [en]

Ecfd:ecfd 5th edition

2022-01-31T09:48:55Z

Abarge: /* Turbulent flows - P. Bénard, CORIA */

{{DISPLAYTITLE: ECFD workshop, 5th edition, 2022}}

== Description ==
{| align="right" style="text-align:center;" cellpadding="2"
| [[File:Logo_ECFD5.png | center | thumb | 350px | ECFD5 workshop logo.]]
|}
* Event from '''23th to 28th of January 2022'''
* Location: [https://www.bonsejour-laplage.com/vacances-tout-compris Centre Bonséjour], Merville-Franceville, near Caen (14)
* Two types of sessions:
** common technical presentations: roadmaps, specific points.
** mini-workshops. Potential workshops are listed below.
* Free of charge
* More than 50 participants from academics (CERFACS, CORIA, IMAG, LEGI, EM2C, UMONS, UVM, VUB, UCL, TUDelft), HPC center/experts (GENCI, AMD, CINES, CRIANN) and industry (Safran, Ariane Group, Siemens-Gamesa).

* Objectives
** Bring together experts in high-performance computing, applied mathematics and multi-physics CFDs
** Identify the technological barriers of exaflopic CFD via numerical experiments
** Identify industrial needs and challenges in high-performance computing
** Propose action plans to add to the development roadmaps of the CFD codes

== News ==

* 03/11/2021: First announcement of the '''5th Extreme CFD Workshop & Hackathon''' !

[[File:Banniere_ECFD5_sponso.png|text-bottom|600px]]

* 13/01/2022: After discussions with the participants, the '''5th Extreme CFD Workshop & Hackathon''' is maintained as an in-person event! It will be also possible to attend to the plenary sessions and participate remotely to the workshop.

* 14/01/2022: The [[#Agenda|ECFD5 program]] is online! The plenary sessions will be announced soon!

* 20/01/2022: The plenary sessions are now defined:
** P1 - 24/01/2022: GPU porting challenges and quantum computing, présentation machine Adastra by G. Staffelbach (CERFACS) + Presentation of the new cluster from CINES called Adastra by C. Andrieu (CINES)
** P2 - 25/01/2022: News, perspectives and future of GPU computing applied to CFD by A. Toure (AMD)
** P3 - 26/01/2022: Theory, applications and perspectives of the Lattice-Boltzmann Method by P. Boivin (M2P2)
** P4 - 27/01/2022: Concepts and notions of mesh adaptation by C. Dapogny (LJK)

* 23/04/2022: '''The ECFD5 event has now started !!''' [https://www.linkedin.com/feed/update/urn:li:activity:6891053385072594944| LinkedIn post]

== Agenda ==

[[File:ECFD5_program.png|text-bottom|600px]]

== Thematics / Mini-workshops ==

These mini-workshops may change and cover more or less topics. This page will be adapted according to your feedback.

=== Combustion - K. Bioche, VUB ===

* '''Sub-project 1: H2/air jet-in-cross-flow numerical simulations (R. Le Dortz, E. Riber, Q. Douasbin)'''

The use of hydrogen as an aviation fuel requires new combustion chamber design. Among strategies to prevent flame flashback and low flame residence time, the micromix injection system is further studied by ENABLEH2. This systems corresponds to a multitude of H2/air jet-in-cross-flow configurations. A 3D numerical simulation with realistic thermodynamics and kinetics is now tractable thanks to massively parralel computing. This week saw the completion of the first steps towards the establishment of a complete simulation. (I) The non-reactive air injection in the combustion chamber. (II) The cross-injection of H2 without ignition. (III) The ignition of this mixture modeled with the skeletal kinetic mechanism of Boivin (H2, H, O2, OH, O, H2O, HO2, H2O2, N2). Further work will be realised concerning mesh refinement, modelling of NOx and porting of the computation on GPU.

* '''Sub-project 2: LES calculation of the MICADO test rig with multicomponent jetA1 (S. Puggelli, T. Lesaffre, E. Riber, B. Cuenot)'''

The EU-funded project ALTERNATE has the goal of exploring the possibility for a wider utilisation of aviation sustainable fuels. A part of the project deals with the assessment of the effect of SAFs on soot production: using the experimental information obtained at ONERA in high-pressure conditions on the MICADO test rig, the effect of Alcohol to Jet (ATJ-SPK) fuel on soot levels are assessed and compared with standard jet A1 emissions. During the project, STech and CERFACS are working jointly on the numerical modelling of soot emissions for jet-A1 and ATJ-SPK combustion in AVBP. Starting from the numerical setup under-development for jet-A1, the worshop permitted to: (I) Switch from a 2-step kinetic mechanism to a complex 29 species, 233 reacs and 15 QSS mechanism. This transition was efficiently conducted with the tool Multi Table Generator. (II) At this stage, an assessment of the effects of the flame sensor on the calculation results was carried out, indicating the consistent behaviour of a recently developped sensor w.r.t classical tools. (III) Switch towards a multicomponent formulation of jet-A1 and assessment of the effect of such advanced approach with respect to the single-component formulation previously employed. Further work will be realised to manage the stiffness of employed kinetics and to compare jet-A1 and ATJ-SPK fuels from a chemical point of view.

* '''Sub-project 3: Euler-Lagrange Multigrid Simulation (T. Lesaffre, O. Vermorel, E. Riber, B. Cuenot)'''

In Lagrange simulations, the point-source approach is based on a ponctual approximation of the particule and requires this last to be smaller than the mesh. The very fine meshes required to represent the Eulerian phase of Euler-Lagrange two-phase flow simulations can lead to a non-validity of the point-source hypothesis. This project aimed at implementing, in the AVBP solver, the simultaneous management and coupling of several simulations. During this week, the Eulerian and Lagrangian phase were successfuly computed on two different meshes and coupled via the CWIPI library. The good behaviour of this framework was assessed on a 1D Evaporation of kerosene droplets in an air stream test case. Encouraging preliminary performance results were obtained on a 3D injection case and require further work.

* '''Sub-project 4: Devolatilization modelling for biomass combustion (K. Bioche, L. Bricteux)'''

Biomass combustion simulations require the modelling of numerous physical phenomena: particle drying, devolatilization, gas-phase combustion, chars oxidation. Besides, the valorisation chains for biomass include fluidized bed reactors, fixed bed reactors and pulverized fuel burners. The Granular Flow Solver of YALES2 offers a good framework for the simulation of fluidized bed reactors and is functionnaly coupled with the reactive gas-phase solver of the same code. This week permitted to partically implement the modelling of devolatilization in this solver. A single-step kinetic scheme is considered for the particle mass evolution equation while the particle diameter evolves during the process. Further work is necessary to account for the thermal and mass couplings with the fluid phase.

* '''Sub-project 5: Thickened-Flame LES model in a Lattice-Boltzmann Method framework (P. Boivin, S. Zhao, M. Le Boursicaud)'''

The TFLES framework of the hybrid Lattice-Boltzmann sover ProLB was extended to account for recent sensor methods. During this week, a smooth flame sensor based on the curvature of the norm of the advancement variable gradient was developped. Also for filtering operations, the lattice requires to access data over three neighboring layers. A precise and continuous thickening factor was obtained with such method.

* '''Sub-project 6: NOx modeling applied to KIAI combustion chamber (J. Obando, P. Bénard, V. Moureau)'''

This project treated of the implementation of NOx modeling into simulations of the KIAI combustion chamber, experimentaly studied at CORIA lab. During this week, various NOx modeling strategies were listed. Associated kinetic mechanisms, among which analytical chemisty, were employed for 1D flame simulations in YALES2 solver. Further work include the use of such methods on the 3D computational case.

=== Static and dynamic mesh adaptation - G. Balarac, LEGI ===

=== Multi-phase flows - M. Cailler, SAFRAN TECH ===

* '''Sub-project 1: Hybrid E-E/E-L two-phase flow method (M. Cailler, F. Pecquery, I. El Yamani, V. Moureau)'''

The High-Fidelity approach based on ACLS & DMA allows a reliable description of interface dynamics. For design exploration, low-CPU methods with controlled level of fidelity are required. An interesting approach to reduce CPU cost relies on an hybrid approach based on an Eulerian representation of the gas & and a Lagrangian description for the liquid. Objective of the ECFD5 was to explore the capability to reconstruct the interface normal on the Eulerian grid. A level-set based strategy relying on Geometric Multiple Markers Projection (Janodet et al., 2022) has been first tested showing good capabilities providing that the iso-surface distance equal 0 is captured. An alternative strategy based on the liquid volume fraction has been tested.

* '''Sub-project 3: Convergence of the interface curvature computation (G. Ghigliotti, J. Carmona, G. Balarac, G. Lartigue)'''

The computation of interface curvature in a level-set framework is based on the classic formula as divergence of the gradient of the levelset function. This function being computed at 2nd order, one obtains a O(0) curvature, meaning that the error does not decrease with mesh refinement.
We have implemented in YALES2 a strategy proposed by Emmanuel Maître and collaborators in a finite element method based on the regularization (filtering) of the level-set gradient and curvature.
This strategy has been tested for the simple test case of a static circular interface.
We used two types of filters (simple gather-scatter or bilaplacian as developed by Lola Guedot (PhD thesis 2015)) on different mesh types (split quadrilaterals, isotropic triangular mesh, unstructured triangular mesh).
The results are encouraging since a O(1) convergence is obtained in all cases.
Further work is needed to tune the filter properties (amplitude and size) for different spatial resolutions and levelset "narrow band" width.

* '''Sub-project 4: Conservative two-fluid momentum transport (F. Pecquery, C. Merlin, M. Cailler, J. Carmona, V. Moureau)'''

=== Numerics - G. Lartigue, CORIA ===

=== Turbulent flows - P. Bénard, CORIA ===
* '''Sub-project 1: Optimization of the actuator set for several wind turbines in YALES2 (F. Houtin Mongrolle, S. Gremmo, E. Muller & B. Duboc)'''

* '''Sub-project 2: Thermal effect in an atmospheric solver (U. Vigny, L. Voivenel, S. Zeoli, P. Benard)'''
Given the current environmental and energy challenges, maximising the wind farm electricity production is essential. Therefore, it becomes necessary to develop the most reliable and accurate prediction and simulation tools. Following this tenet, an atmospheric solver, which will take into account meteorological phenomena, should be developed. The preliminary work, going from bibliography study to road map was performed during the extreme cod workshop. Thus five parts have been identified:
(I) The YALES2 Variable Density Solver (VDS) will be used because of the need to take into account buoyancy effect including for big density differences.
(II) A wall law correction term, relative to atmospheric boundary layer will be added.
(III) The actuator line method used to simulate wind turbine will be extended to VDS, modifying the velocity source term to a momentum source term.
(IV) The Coriolis effects, depending on the latitude will be implemented.
(V) The wall heat flux, allowing to simulate diurnal and nocturnal cycles on various terrains, is more realistic than a target wall temperature.
From this work, future development are now clear and just waiting to be developed.

* '''Sub-project 5: TBLE wall model for LES with pressure gradient on a simple turbomachinery geometry (M. Cizeron, N. Odier, R. Vicquelin)'''
Wall modeling is often used in LES to alleviate the computational cost that would be required to resolve all the length scales up to the solid boundaries of the domain. The classical way of doing it is by using an algebraic model to provide the wall friction and heat flux, with a coupling to the LES solver at the first off-wall nodes. The wall model was designed from analyzing RANS equation with strong assumptions such as planar flow, equilibrium and no pressure gradient. These assumptions are often far from true in real applications, such as turbomachinery applications, where the use of a wall model is mandatory due to the size of the calculation. During this workshop, a wall model relying on the resolution of the Thin Boundary Layer Equations (TBLE) was studied, which had been implemented by EM2C. The addition of a pressure gradient to these equations has been conducted and tested, at first only for the 1D wall model solver, then on a 3D turbulent channel. It remains to be tested on a diffuser configuration with a real pressure gradient to quantify the effect of the new wall model. The influence of the point considered to do the coupling between the LES and the wall model (ie. its distance to the wall) has also been tested both for the TBLE and the original algebraic model, showing that coupling farther from the wall yields better results and reduces the so-called log-layer mismatch.

* '''Sub-project 6: Tools for rough wall modelling (A. Barge, S. Meynet)'''
Within the STREAM project framework, a roughness-resolved Large-Eddy Simulation (RRLES) database is being built. The aim of this latter is to be representative of rough channel flows, especially for additive-manufacturing heat exchangers. First RRLES have already been performed. From turbulence and rough wall stress statistics analysis of the results, a first stochastic model, which reproduces the statistical behavior of the wall stress vector, have been proposed. The modeled wall stress allows a better prediction of the pressure drop in a flat wall channel compared to the use of the mean value of the wall stress measured in RRLES alone. However, the near wall region is still mispredicted and the model is correlated in time but not in space. The aim of this ECFD5 was to develop tools to improve modelling and explore new ways. A roughness mapping tool for smooth surfaces have been implemented into YALES2 to get local surface height. This tool is based on an existing in-house surface roughness generator developed for the STREAM project. The idea is to use the map to generated space correlated fluctuations for the wall shear stress. Some bugs still remain to fully use this tool. In parallel, the modelling approach was extended to passive scalar, especially for temperature. To this end, new random tools as white noise, unit sphere random walk and Gaussian / Log-normal stochastic processes have been coded. Finally, the idea of using walls as velocity source terms emerged during this ECFD5. The principle is to mask a grid layer above the wall and to transport the rough map on this grid to estimate the roughness effects above the wall. Parametrizing and testing these tools remained to be done at the end of ECFD5.

=== Compressible - L. Bricteux, UMONS ===

=== User experience - J. Leparoux, SAFRAN TECH ===

* '''Sub-project 1: Multi combustion model chemtable generator (S. Dillon, R. Mercier)'''

* '''Sub-project 2: Task-driven automatic run sequence (R. Mercier, J. Leparoux, M. Cailler, R. Letournel)'''

* '''Sub-project 3: YALES2 Tools & Gitlab CI (J. Leparoux, A. Tstetoglou)'''

* '''Sub-project 4: Wind energy tools (E. Muller, S. Gremmo, F. Houtin-Mongrolle, B. Duboc)'''

=== Hackathon - G. Staffelbach, CERFACS ===
* '''Participants: I. d'Ast, J. Legaux, G. Staffelbach, P. Begou, G. Lartigue, V. Moureau, A. Toure, C. Laurie, S. Delamare, C. Andrieu, C. Jourdain'''
AMD GPU hardware is still relatively unknown in our CFD community. This hackathon was the opportunity to deep dive into the AMD dev environment to prepare the arrival of AdAstra at CINES.
Both YALES and AVBP have been ported to the AOMP framework using ROCm 4.5 on the GRID5000 Neowise system.
CPU execution posed no issues and we were able to focus on GPU Offloading using OpenMP.
On the YALES2 side, a mini-app encompassing the typical YALES2 structure hierarchy and loop execution was extracted from the code to evaluate different porting strategies and on the AVBP side the current OpenACC GPU offloading was translated to OpenMP focusing on the viscosity computation kernel.
We learnt that the current supported standard of OpenMP in ROCm 4.5 does not allow for direct offloading of reference values inside an derived type structure but is was possible to use aliases such as pointers or flat array copies to do the job. This should be solved with the support of OpenMP 5.0
Another troublesome issues, was the lack of support for offloading of array vector operations (ex : array(:) = 1.0 ) rendering the explicitation of the loops for these manadatory.

Some bugs remain and it is encouraged to use the latest compiler version when working on the porting ( the release of flang 14.0.1 saved us a lot of time as we had started with 14.0.0 ).
Offloading of the miniapp of YALES2 yielded a times 60 acceleration of the kernel whereas the offloading of the viscosity model in a full avbp simulation yielded an 7 times factor in performance when comparing on core to one GPU. These results are to be taken with a grain of salt but are really encouraging.

For the next steps, a porting strategy for both codes will be implemented (depending on the OpenMP 5 support ) and discussions are underway with CINES and other partners so as to offer the best experience to both code's communities on AdAstra at its release.

Ecfd:ecfd 5th edition

2022-01-31T09:46:35Z

Abarge: /* Turbulent flows - P. Bénard, CORIA */

{{DISPLAYTITLE: ECFD workshop, 5th edition, 2022}}

== Description ==
{| align="right" style="text-align:center;" cellpadding="2"
| [[File:Logo_ECFD5.png | center | thumb | 350px | ECFD5 workshop logo.]]
|}
* Event from '''23th to 28th of January 2022'''
* Location: [https://www.bonsejour-laplage.com/vacances-tout-compris Centre Bonséjour], Merville-Franceville, near Caen (14)
* Two types of sessions:
** common technical presentations: roadmaps, specific points.
** mini-workshops. Potential workshops are listed below.
* Free of charge
* More than 50 participants from academics (CERFACS, CORIA, IMAG, LEGI, EM2C, UMONS, UVM, VUB, UCL, TUDelft), HPC center/experts (GENCI, AMD, CINES, CRIANN) and industry (Safran, Ariane Group, Siemens-Gamesa).

* Objectives
** Bring together experts in high-performance computing, applied mathematics and multi-physics CFDs
** Identify the technological barriers of exaflopic CFD via numerical experiments
** Identify industrial needs and challenges in high-performance computing
** Propose action plans to add to the development roadmaps of the CFD codes

== News ==

* 03/11/2021: First announcement of the '''5th Extreme CFD Workshop & Hackathon''' !

[[File:Banniere_ECFD5_sponso.png|text-bottom|600px]]

* 13/01/2022: After discussions with the participants, the '''5th Extreme CFD Workshop & Hackathon''' is maintained as an in-person event! It will be also possible to attend to the plenary sessions and participate remotely to the workshop.

* 14/01/2022: The [[#Agenda|ECFD5 program]] is online! The plenary sessions will be announced soon!

* 20/01/2022: The plenary sessions are now defined:
** P1 - 24/01/2022: GPU porting challenges and quantum computing, présentation machine Adastra by G. Staffelbach (CERFACS) + Presentation of the new cluster from CINES called Adastra by C. Andrieu (CINES)
** P2 - 25/01/2022: News, perspectives and future of GPU computing applied to CFD by A. Toure (AMD)
** P3 - 26/01/2022: Theory, applications and perspectives of the Lattice-Boltzmann Method by P. Boivin (M2P2)
** P4 - 27/01/2022: Concepts and notions of mesh adaptation by C. Dapogny (LJK)

* 23/04/2022: '''The ECFD5 event has now started !!''' [https://www.linkedin.com/feed/update/urn:li:activity:6891053385072594944| LinkedIn post]

== Agenda ==

[[File:ECFD5_program.png|text-bottom|600px]]

== Thematics / Mini-workshops ==

These mini-workshops may change and cover more or less topics. This page will be adapted according to your feedback.

=== Combustion - K. Bioche, VUB ===

* '''Sub-project 1: H2/air jet-in-cross-flow numerical simulations (R. Le Dortz, E. Riber, Q. Douasbin)'''

The use of hydrogen as an aviation fuel requires new combustion chamber design. Among strategies to prevent flame flashback and low flame residence time, the micromix injection system is further studied by ENABLEH2. This systems corresponds to a multitude of H2/air jet-in-cross-flow configurations. A 3D numerical simulation with realistic thermodynamics and kinetics is now tractable thanks to massively parralel computing. This week saw the completion of the first steps towards the establishment of a complete simulation. (I) The non-reactive air injection in the combustion chamber. (II) The cross-injection of H2 without ignition. (III) The ignition of this mixture modeled with the skeletal kinetic mechanism of Boivin (H2, H, O2, OH, O, H2O, HO2, H2O2, N2). Further work will be realised concerning mesh refinement, modelling of NOx and porting of the computation on GPU.

* '''Sub-project 2: LES calculation of the MICADO test rig with multicomponent jetA1 (S. Puggelli, T. Lesaffre, E. Riber, B. Cuenot)'''

The EU-funded project ALTERNATE has the goal of exploring the possibility for a wider utilisation of aviation sustainable fuels. A part of the project deals with the assessment of the effect of SAFs on soot production: using the experimental information obtained at ONERA in high-pressure conditions on the MICADO test rig, the effect of Alcohol to Jet (ATJ-SPK) fuel on soot levels are assessed and compared with standard jet A1 emissions. During the project, STech and CERFACS are working jointly on the numerical modelling of soot emissions for jet-A1 and ATJ-SPK combustion in AVBP. Starting from the numerical setup under-development for jet-A1, the worshop permitted to: (I) Switch from a 2-step kinetic mechanism to a complex 29 species, 233 reacs and 15 QSS mechanism. This transition was efficiently conducted with the tool Multi Table Generator. (II) At this stage, an assessment of the effects of the flame sensor on the calculation results was carried out, indicating the consistent behaviour of a recently developped sensor w.r.t classical tools. (III) Switch towards a multicomponent formulation of jet-A1 and assessment of the effect of such advanced approach with respect to the single-component formulation previously employed. Further work will be realised to manage the stiffness of employed kinetics and to compare jet-A1 and ATJ-SPK fuels from a chemical point of view.

* '''Sub-project 3: Euler-Lagrange Multigrid Simulation (T. Lesaffre, O. Vermorel, E. Riber, B. Cuenot)'''

In Lagrange simulations, the point-source approach is based on a ponctual approximation of the particule and requires this last to be smaller than the mesh. The very fine meshes required to represent the Eulerian phase of Euler-Lagrange two-phase flow simulations can lead to a non-validity of the point-source hypothesis. This project aimed at implementing, in the AVBP solver, the simultaneous management and coupling of several simulations. During this week, the Eulerian and Lagrangian phase were successfuly computed on two different meshes and coupled via the CWIPI library. The good behaviour of this framework was assessed on a 1D Evaporation of kerosene droplets in an air stream test case. Encouraging preliminary performance results were obtained on a 3D injection case and require further work.

* '''Sub-project 4: Devolatilization modelling for biomass combustion (K. Bioche, L. Bricteux)'''

Biomass combustion simulations require the modelling of numerous physical phenomena: particle drying, devolatilization, gas-phase combustion, chars oxidation. Besides, the valorisation chains for biomass include fluidized bed reactors, fixed bed reactors and pulverized fuel burners. The Granular Flow Solver of YALES2 offers a good framework for the simulation of fluidized bed reactors and is functionnaly coupled with the reactive gas-phase solver of the same code. This week permitted to partically implement the modelling of devolatilization in this solver. A single-step kinetic scheme is considered for the particle mass evolution equation while the particle diameter evolves during the process. Further work is necessary to account for the thermal and mass couplings with the fluid phase.

* '''Sub-project 5: Thickened-Flame LES model in a Lattice-Boltzmann Method framework (P. Boivin, S. Zhao, M. Le Boursicaud)'''

The TFLES framework of the hybrid Lattice-Boltzmann sover ProLB was extended to account for recent sensor methods. During this week, a smooth flame sensor based on the curvature of the norm of the advancement variable gradient was developped. Also for filtering operations, the lattice requires to access data over three neighboring layers. A precise and continuous thickening factor was obtained with such method.

* '''Sub-project 6: NOx modeling applied to KIAI combustion chamber (J. Obando, P. Bénard, V. Moureau)'''

This project treated of the implementation of NOx modeling into simulations of the KIAI combustion chamber, experimentaly studied at CORIA lab. During this week, various NOx modeling strategies were listed. Associated kinetic mechanisms, among which analytical chemisty, were employed for 1D flame simulations in YALES2 solver. Further work include the use of such methods on the 3D computational case.

=== Static and dynamic mesh adaptation - G. Balarac, LEGI ===

=== Multi-phase flows - M. Cailler, SAFRAN TECH ===

* '''Sub-project 1: Hybrid E-E/E-L two-phase flow method (M. Cailler, F. Pecquery, I. El Yamani, V. Moureau)'''

The High-Fidelity approach based on ACLS & DMA allows a reliable description of interface dynamics. For design exploration, low-CPU methods with controlled level of fidelity are required. An interesting approach to reduce CPU cost relies on an hybrid approach based on an Eulerian representation of the gas & and a Lagrangian description for the liquid. Objective of the ECFD5 was to explore the capability to reconstruct the interface normal on the Eulerian grid. A level-set based strategy relying on Geometric Multiple Markers Projection (Janodet et al., 2022) has been first tested showing good capabilities providing that the iso-surface distance equal 0 is captured. An alternative strategy based on the liquid volume fraction has been tested.

* '''Sub-project 3: Convergence of the interface curvature computation (G. Ghigliotti, J. Carmona, G. Balarac, G. Lartigue)'''

The computation of interface curvature in a level-set framework is based on the classic formula as divergence of the gradient of the levelset function. This function being computed at 2nd order, one obtains a O(0) curvature, meaning that the error does not decrease with mesh refinement.
We have implemented in YALES2 a strategy proposed by Emmanuel Maître and collaborators in a finite element method based on the regularization (filtering) of the level-set gradient and curvature.
This strategy has been tested for the simple test case of a static circular interface.
We used two types of filters (simple gather-scatter or bilaplacian as developed by Lola Guedot (PhD thesis 2015)) on different mesh types (split quadrilaterals, isotropic triangular mesh, unstructured triangular mesh).
The results are encouraging since a O(1) convergence is obtained in all cases.
Further work is needed to tune the filter properties (amplitude and size) for different spatial resolutions and levelset "narrow band" width.

* '''Sub-project 4: Conservative two-fluid momentum transport (F. Pecquery, C. Merlin, M. Cailler, J. Carmona, V. Moureau)'''

=== Numerics - G. Lartigue, CORIA ===

=== Turbulent flows - P. Bénard, CORIA ===
* '''Sub-project 1: Optimization of the actuator set for several wind turbines in YALES2 (F. Houtin Mongrolle, S. Gremmo, E. Muller & B. Duboc)'''

* '''Sub-project 2: Thermal effect in an atmospheric solver (U. Vigny, L. Voivenel, S. Zeoli, P. Benard)'''
Given the current environmental and energy challenges, maximising the wind farm electricity production is essential. Therefore, it becomes necessary to develop the most reliable and accurate prediction and simulation tools. Following this tenet, an atmospheric solver, which will take into account meteorological phenomena, should be developed. The preliminary work, going from bibliography study to road map was performed during the extreme cod workshop. Thus five parts have been identified:
(I) The YALES2 Variable Density Solver (VDS) will be used because of the need to take into account buoyancy effect including for big density differences.
(II) A wall law correction term, relative to atmospheric boundary layer will be added.
(III) The actuator line method used to simulate wind turbine will be extended to VDS, modifying the velocity source term to a momentum source term.
(IV) The Coriolis effects, depending on the latitude will be implemented.
(V) The wall heat flux, allowing to simulate diurnal and nocturnal cycles on various terrains, is more realistic than a target wall temperature.
From this work, future development are now clear and just waiting to be developed.

* '''Sub-project 5: TBLE wall model for LES with pressure gradient on a simple turbomachinery geometry (M. Cizeron, N. Odier, R. Vicquelin)'''
Wall modeling is often used in LES to alleviate the computational cost that would be required to resolve all the length scales up to the solid boundaries of the domain. The classical way of doing it is by using an algebraic model to provide the wall friction and heat flux, with a coupling to the LES solver at the first off-wall nodes. The wall model was designed from analyzing RANS equation with strong assumptions such as planar flow, equilibrium and no pressure gradient. These assumptions are often far from true in real applications, such as turbomachinery applications, where the use of a wall model is mandatory due to the size of the calculation. During this workshop, a wall model relying on the resolution of the Thin Boundary Layer Equations (TBLE) was studied, which had been implemented by EM2C. The addition of a pressure gradient to these equations has been conducted and tested, at first only for the 1D wall model solver, then on a 3D turbulent channel. It remains to be tested on a diffuser configuration with a real pressure gradient to quantify the effect of the new wall model. The influence of the point considered to do the coupling between the LES and the wall model (ie. its distance to the wall) has also been tested both for the TBLE and the original algebraic model, showing that coupling farther from the wall yields better results and reduces the so-called log-layer mismatch.

* '''Sub-project 6: Tools for rough wall modelling (A. Barge, S. Meynet)'''
Within the STREAM project framework, a roughness-resolved Large-Eddy Simulation (RRLES) database is being built. The aim of this latter is to be representative of rough channel flows, especially for additive-manufacturing heat exchangers. First RRLES have already been performed. From turbulence and rough wall stress statistics analysis of the results, a first stochastic model, which reproduces the statistical behavior of the wall stress vector, have been proposed. The modeled wall stress allows a better prediction of the pressure drop in a flat wall channel compared to the use of the mean value of the wall stress measured in RRLES alone. However, the near wall region is still mispredicted and the model is correlated in time but not in space. The aim of this ECFD5 was to develop tools to improve modelling and explore new ways. A roughness mapping tool for smooth surfaces have been implemented into YALES2 to get local surface height. This tool is based on an existing in-house surface roughness generator developed for the STREAM project. The idea is to use the map to generated space correlated fluctuations for the wall shear stress. Some bugs still remain to fully use this tool. In parallel, the modelling approach was extended to passive scalar, especially for temperature. To this end, new random tools as white noise, unit sphere random walk and Gaussian / Log-normal stochastic processes have been coded. Finally, the idea of using walls as velocity source terms emerged during this ECFD5. The principle is to mask a grid layer above the wall and to transport the rough map on this grid to estimate the roughness effects above the wall. Parametrizing and testing these tools with rough map remained to be done at the end of ECFD5.

=== Compressible - L. Bricteux, UMONS ===

=== User experience - J. Leparoux, SAFRAN TECH ===

* '''Sub-project 1: Multi combustion model chemtable generator (S. Dillon, R. Mercier)'''

* '''Sub-project 2: Task-driven automatic run sequence (R. Mercier, J. Leparoux, M. Cailler, R. Letournel)'''

* '''Sub-project 3: YALES2 Tools & Gitlab CI (J. Leparoux, A. Tstetoglou)'''

* '''Sub-project 4: Wind energy tools (E. Muller, S. Gremmo, F. Houtin-Mongrolle, B. Duboc)'''

=== Hackathon - G. Staffelbach, CERFACS ===
* '''Participants: I. d'Ast, J. Legaux, G. Staffelbach, P. Begou, G. Lartigue, V. Moureau, A. Toure, C. Laurie, S. Delamare, C. Andrieu, C. Jourdain'''
AMD GPU hardware is still relatively unknown in our CFD community. This hackathon was the opportunity to deep dive into the AMD dev environment to prepare the arrival of AdAstra at CINES.
Both YALES and AVBP have been ported to the AOMP framework using ROCm 4.5 on the GRID5000 Neowise system.
CPU execution posed no issues and we were able to focus on GPU Offloading using OpenMP.
On the YALES2 side, a mini-app encompassing the typical YALES2 structure hierarchy and loop execution was extracted from the code to evaluate different porting strategies and on the AVBP side the current OpenACC GPU offloading was translated to OpenMP focusing on the viscosity computation kernel.
We learnt that the current supported standard of OpenMP in ROCm 4.5 does not allow for direct offloading of reference values inside an derived type structure but is was possible to use aliases such as pointers or flat array copies to do the job. This should be solved with the support of OpenMP 5.0
Another troublesome issues, was the lack of support for offloading of array vector operations (ex : array(:) = 1.0 ) rendering the explicitation of the loops for these manadatory.

Some bugs remain and it is encouraged to use the latest compiler version when working on the porting ( the release of flang 14.0.1 saved us a lot of time as we had started with 14.0.0 ).
Offloading of the miniapp of YALES2 yielded a times 60 acceleration of the kernel whereas the offloading of the viscosity model in a full avbp simulation yielded an 7 times factor in performance when comparing on core to one GPU. These results are to be taken with a grain of salt but are really encouraging.

For the next steps, a porting strategy for both codes will be implemented (depending on the OpenMP 5 support ) and discussions are underway with CINES and other partners so as to offer the best experience to both code's communities on AdAstra at its release.

Ecfd:ecfd 5th edition

2022-01-28T03:37:21Z

Abarge: /* Turbulent flows - P. Bénard, CORIA */

File:Ecfd3 final project7.pdf

2020-01-31T11:02:42Z

Abarge:

Ecfd:ecfd 3rd edition

2020-01-31T11:00:48Z

Abarge: /* Project #7: Modélisation de parois pour la simulation des grandes échelles */

{{DISPLAYTITLE: ECFD workshop, 3rd edition, 2020}}
__NOTOC__

== Sponsors ==

[[File:ecfd3_sponsors.png|center|frameless|800px]]

== Participants ==

[[File:ecfd3_participants.png|center|frameless|1000px]]

[[File:lecfd3_participants_photo.jpg|center|frameless|1000px]]

== Flyer ==

* [[media:ecfd3_flyer.pdf | Flyer]]

== Presentations ==

* [[media:ecfd3_intro.pdf | Introduction workshop]]
* [[media:ecfd3_intro_genci.pdf | Introduction GENCI]]
* [[media:ecfd3_avbp_roadmap_HPC.pdf | Roadmap AVBP (HPC)]]
* [[media:ecfd3_yales2_roadmap.pdf | Roadmap YALES2]]

== Booklet ==

* [[media:ecfd3_booklet_template.zip | Template]]

== Project achievements ==

=== Project #1: Hackathon GENCI/ATOS/AMD/CERFACS on AVBP ===

''C. Piechurski (GENCI), S. Jauré (ATOS), B. Pajot (ATOS), P.-A. Harraud (AMD), P. Mohanamuraly (CERFACS), G. Staffelbach (CERFACS), J. Legaux (CERFACS)''

We ported the AVBP solver to the AMD Rome system available at GENCI -TGCC ( IRENE Joliot Curie).
Characterisation of the application on the architecture showed a 1/3 performance dependency to bandwidth and 2/3 to compute.
Strong scaling performance up to 130k cores was measured with openmpi and provided an acceleration of 75% without optimisations.
Weak scaling up to 32k MPI ranks suggests that decimation of the processes by a factor 2 improves computational efficiency by up to 30%.
This suggests a trade off between mpi imbalance and decimation is possible if imbalance is higher than 30% to improve time to solution.

Currently Openmpi offers the best perfofrmance, intelmpi is still a bit unstable.

During the Hackathon we also introduced colour based cache blocking using ColPack in the code in order to use OpenMP without critical sections.
On a 2x18 core Skylake processor the new implementation offered similar speedup using full threading versus full MPI with the best trade off being 4 MPI and 9 threads per MPI.
On AMD Rome, Full threading did not offer much acceleration and needs to be inversigated but 8 MPI and 16 threads per MPI seem quite promising.

[[media:ecfd3_final_project1.pdf | Final presentation of project #1]]

=== Project #2: Hackathon GENCI/ATOS/AMD/CORIA on YALES2 ===
''C. Piechurski (GENCI), S. Jauré (ATOS), P.-A. Harraud (AMD), P. Mohanamuraly (CERFACS), G.Lartigue (CORIA), F. Gava (CORIA), K. Bioche (CORIA), P. Begou (LEGI)''

[[media:ecfd3_final_project2.pdf | Final presentation of project #2]]

=== Project #3: Implementation of a secondary atomization model in YALES2 ===

''C. G. Guillamon (Safran Tech), L .Voivenel (Safran Tech), R. Mercier (Safran Tech)''

In Lagrangian simulations, droplets are transported following a ballistic motion in an eulerian mesh. For non-reactive environments, droplets might undergo secondary atomization due to the aerodynamic interaction. In this work, we implement in YALES2 a breakup model known as Taylor-Analogy Breakup (TAB). This model is based on the analogy between a droplet and a second-order mechanical system, hence making possible to determine the breakup behaviour by means of Newton's second law.

Another model, the stochastic breakup model by Gorokhovski, is also suggested for future work and will be implemented in YALES2.

[[media:ecfd3_final_project3.pdf | Final presentation of project #3]]

=== Project #4: Conservative Heat Transfers in the the Accurate Conservative Level-Set framework ===

''François Pecquery (ARIANE GROUP), Mélody Cailler (SAFRAN TECH), Romain Janodet (SAFRAN TECH/CORIA) and Vincent Moureau (CORIA)''

Objectives of the project was to introduce conservative heat transfers in the Accurate Conservative Level-Set framework to be able to describe heat transfers and liquid dynamics in an accurate, robust and conservative manner. A Multi-Phase Transport solver is introduced relying on the conserving and level-set coherent transport of the temperature. The solution is to use the fluxes of a phase indicator that may be sharp, contrarily to the level-set. The new solver was used on a simplified test case where a liquid droplet is transported in a temperature stratified environment. Results show promising capabilities of the new framework. Next work include improvement of the transport equation stability, and of the jump condition at the interface.

[[media:ecfd3_final_project4.pdf | Final presentation of project #4]]

=== Project #5: Jet-in-crossflow par une méthode d’interface diffuse ===

''T. Laroche, N. Odier, B. Cuenot (CERFACS). In collaboration with M. Pelletier, T. Schmitt, S. Ducruix (EM2C)''

In the context of fuel injection in an aircraft engine, liquid fuel is injected through a swirler, and sheared by a high-speed oxyder which destabilizes the liquid interface. This interaction induces liquid ligaments, which break up into large droplets (primary atomization), and then themselves break into small droplets (secondary atomization)
This project deals with the implementation of a diffuse-interface method in the massively parallel solver AVBP to represent the liquid interface destabilization during primary atomization for compressible applications. This methodology is found to be very efficient, however a control of the interface diffusion is mandatory as soon as convective effects are added. During this workshop, the methodology proposed by Chiodi and Desjardins ( ''A reformulation of the conservative level set reinitialization equation for accurate and robust simulation of complex multiphase flows'', JCP 2017) to control the interface thickness has been implemented in AVBP, and is currently under validation on a periodic liquid jet with surface tension effects.

[[media:ecfd3_final_project5.pdf | Final presentation of project #5]]

=== Project #6: Accurate numerical predicti􏴇on of vorti􏴇cal flows using AMR ===

We try to demonstrate that Eulerian method YALES2 using AMR can do a very good job to capture complex vortical flows at moderate Re=10k
Here we use an AMR strategy based on vorticity. We investigate the problem of vortex ring collision. We have a gain of 1000 on the numbers of elements compared
to a non adaptative approach. We are able to capture the transition from a very simple laminar flow to a complex turbulent flow.

[[media:ecfd3_final_project6.pdf | Final presentation of project #6]]

=== Project #7: Modélisation de parois pour la simulation des grandes échelles ===

[[media:ecfd3_final_project7.pdf | Final presentation of project #7]]

''A. Barge(LEGI), P. Bénard(CORIA) and G. Balarac(LEGI)''

We ran simulations to benchmark the Dynamic Slip Wall method from (Bose & Moin, PoF, 2014) that we implemented in YALES2. The performances of the method have been compared with those from the classic Log-Law and the method from (Duprat et al., PoF, 2011) on the standard cases of channel flow and periodic hills. The results from the Dynamic Slip wall showed a satisfying efficiency although its precision stays comparable to the method from Duprat et al. Also, we set up the non-stationary test case of oscillating channel flow to enrich the benchmarking with the above-mentioned methods. Finally, we started to work on the implementation of a new approach proposed by M. Gorokhovski, tests are in progress.

=== Project #8: Accurate numerical simulation of contact lines with dynamic mesh adaptation ===
''S. Pertant (LEGI), G. Ghigliotti (LEGI), G. Balarac (LEGI)''

The main objective of this project was to develop a methodology to simulate contact lines on unstructured meshes. We especially wanted to get rid of mesh influence on contact line movement when the flow is driven by surface tension and the contact line close to its equilibrium position. A slight modification in the Ghost Fluid Method to apply the pressure jump has been tested and seems promising. The pressure gradient at contact line is indeed less sensitive to mesh elements for high density ratios. Furthermore, dynamic mesh adaptation has been used to simulate a 2D vapour bubble lying on a wall. Due to gravity, the two contact lines are receding until their merging and the bubble departure. The mesh remains fine to capture the contact line dynamics. As a future work, we plan to perform mesh adaptation on 3D contact line cases and to include additional physics such as contact angle imposition (already implemented but not used yet with mesh adaptation).

[[media:ecfd3_final_project8.pdf | Final presentation of project #8]]

=== Project #9: Remeshed particle method at high Schmidt and Reynolds number ===

''S. Santoso (LJK), J.-B. Lagaert (Math Orsay), G.Balarac (LEGI)''

We study the advection of a scalar function in turbulent flows with a multimesh method. The finite volume method is used to solve Navier-Stokes equations on an unstructured mesh (YALES2). The advection equation is solved with remeshed particle method on a cartesian mesh. In the context of parallel computing, we face a very unbalanced problem since a large number of particles are created in a very fine meshed zone. Our strategy to load-balance the problem is to give a weight to every element group which is equal to the density of particle.

[[media:ecfd3_final_project9.pdf | Final presentation of project #9]]

=== Project #10: Adaptive mesh refinement for turbulent premixed combustion ===
''W. Agostinelli, O. Dounia, , T. Jaravel, O. Vermorel

The objective of the project was to evaluate the potential of adaptive mesh refinement (AMR) for premixed combustion in unsteady systems. Three target cases were identified: a semi-vented deflagration with laminar to turbulent transition, a planar detonation wave, and a bluff-body stabilized burner subjected to thermoacoustic oscillations. The simulations were performed with AVBP and coupled to the AMR implementation of YALES2. Several metrics and remeshing criterions were developed to identify and correctly resolve both the combustion wave front and the turbulent flow. The comparison of numerical results with reference simulations showed that the main features of the physics could be recovered with a significant speed-up in term of computational cost.

[[media:ecfd3_final_project10.pdf | Final presentation of project #10]]

=== Project #11: Multiphysics coupling for wind turbine wake modeling ===

''F.Houtin-Mongrolle (CORIA), B. Duboc (SGRE), P. Benard (CORIA)''

The goal of this project was to evaluate the coupling of YALES2 (flow solver) and BHawC(Aero-Servo-Elastic solver).

[[media:ecfd3_final_project11.pdf | Final presentation of project #11]]

=== Project #12: Stability of a semi-implicit compressible cavitation solver ===

''H. Garg (LEGI), G. Ghigliotti (LEGI) and G. Balarac (LEGI)''

The compressible cavitation solver is used to simulate cavitation inception in an initially liquid flow behind an obstacle.
This solver is based on the implicit compressible solver, that has been modified to include a « barotropic » pressure-density relationship playing the role of an equation of state independent from the temperature.
While this strategy has proven to be effective for DNS simulations of the implosion of vapour bubbles, the simulation of cavitation inception in an initially liquid flow was leading to strong instabilities in the simulation shortly after the appearence of vapour.
The test case chosen is a flow behind a 2D cylinder.
The analysis of the results has shown that instabilities were correlated with very low (and even unphysically negative) values of the pressure, that were triggering negative density values leading to code instability.
Using limiters to ensure a positive pressure and a density within the range of the equation of state improved the stability and allowed to perform a preliminary simulation of a cavitating flow behind an obstacle.
Ultimately instabilities appear anyways, so that the will look to the spatial discretisation schemes.

[[media:ecfd3_final_project12.pdf | Final presentation of project #12]]

=== Project #13: Validations and comparisons of Diffuse / Sharp interface methods in a structured DNS solver (Titan) ===
''V. Boniou (EM2C), J.M. Dupays (EM2C), M. Pelletier (EM2C), T. Schmitt (EM2C), A. Vié (EM2C)

The project aimed at using academic test cases to compare the sharp (incompressible) and diffuse (compressible) models. In particular, the test case of an inviscid initially elliptical oscillating droplet has been carried out.
The solvers features are the following:

- incompressible VOF solver (sharp): Numerical Method: Projection Method, Interface reconstruction: VOF, Surface tension: CSF

- compressible multifluid solver (diffuse): Advection scheme: MUSCL + RK2 + minmod limiter, Surface tension: CSF.

The source term is integrated with operator-splitting, and the curvature computation relies on a 2nd-order differentiation of the liquid volume fraction, which is previously smooth by filtering.
This test case showed good agreement on the oscillation period, while exhibiting a slight numerical diffusion in the incompressible case and a strong numerical diffusion in the compressible case.
In the compressible case, the use of higher-order splitting (Strang [SIAM Num. An. 1968]) has been tested, yielding no noticeable improvement. Reduction of the number of filtering iterations on the liquid volume fraction provides a slight improvement, which may indicate that a better curvature computation could participate to reduce the numerical diffusion.

[[media:ecfd3_final_project13.pdf | Final presentation of project #13]]

=== Project #14: High Order Framework ===
''M. Bernard (LEGI), G. Lartigue (CORIA), G. Balarac (LEGI), V. Moureau (CORIA)''

Aim of this project is to extend the high order framework (HOF) in Yales2.
As a reminder, the HOF permits to reconstruct a point-wise quantity from the volume-averaged one, arising from classical Finite-Volume schemes, and thus to improve spatial accuracy of numerical schemes.

During the ECFD workshop #3, a dedicated solver has been created, the high order solver (hos), duplicated from the incompressible solver (ics).
We started activating the HOF ingredients previously developed, starting from velocity field advancement.
Development is still in progress, but the static Taylor-Green vortices test-case has been investigated in order to see the early improvement.

[[media:ecfd3_final_project14.pdf | Final presentation of project #14]]

=== Project #15: Validation of a fluid structure interaction case with the coupling ALE/SMS ===
''T. Fabbri (LEGI), G. Lartigue (CORIA), G. Balarac (LEGI), V. Moureau (CORIA)''

The objective of this project was the validation of the Turek(2006) benchmark for fluid structure case.
The Structural Mechanics Solver (SMS) was already existing before the workshop, as the coupling with the Arbitrary-Lagrangian Eulerian solver.
However, the results were not in agreement with the case. The data compared here are the flexible part tip displacement, but also the drag and the lift integrated
on the cylinder and the flexible part.
The pure structure test cases were validated, but the forces computed for the pure fluid test cases were not satisfying.
The work of this week was then to improve the viscous shear computation, which implies the wall normal gradient computation.

[[media:ecfd3_final_project15.pdf | Final presentation of project #15]]

=== Project #16: Development of a RANS solver in YALES2 ===
''G. Sahut (LEGI), G. Balarac (LEGI), V. Moureau (CORIA), G. Lartigue (CORIA), P. Bénard (CORIA), A. Grenouilloux (CORIA)''

While the accuracy of LES usually approaches the one of DNS, LES are still too time-consuming for daily use in industrial applications. In this context, we started the development of a RANS solver in YALES2. We are first only interested in the steady state of the solution. In order to remove the CFL constraint, we developed, implemented and validated an implicit projection method for the resolution of the Navier-Stokes equations without turbulence models. The method is based on the implicitation of the velocity predictor ; the Poisson equation and the correction step of the velocity are then solved and applied as in the explicit incompressible solver. We validated the method on a stationary 2D Poiseuille flow with periodic boundary conditions: the simulation runs fine for CFL and Fourier numbers which are inaccessible with the explicit incompressible solver. The advection-diffusion equation for scalars has also been implicited and will be used to add turbulence models to the new implicit incompressible solver developped during this Workshop. More complex boundary conditions will also be addressed in a near future.

[[media:ecfd3_final_project16.pdf | Final presentation of project #16]]

=== Project #17: IMPLEMENTATION OF A COLD PLASMA MODEL IN YALES2 ===

''J.-M. Orlac'h (EM2C), G. Lartigue (CORIA), B. Fiorina (EM2C)''

The objective of this project was to further develop the cold plasma solver in YALES2 in order to accurately model silane nanodusty discharges. The electron temperature equation has been implemented successfully and validated against a reference plasma code. In a second step, a detailed electron kinetics has been implemented in YALES2 in order to couple the electron temperature with the charged species mass fractions. The user can now define a list of reactions whose rates depend on the electron temperature. These improvements open the path to the simulation of nanoparticle production in silane discharges using a Lagrangian description for the nanoparticles.

[[media:ecfd3_final_project17.pdf | Final presentation of project #17]]

=== Project #18: L’Evaporo O Maıtre ===

[[media:ecfd3_final_project18.pdf | Final presentation of project #18]]

=== Project #19: The Clone Wars ===
''H. Maldonado Colman (EM2C), C. Nguyen Van (EM2C - Safran-Tech), R. Mercier (Safran-Tech), B. Fiorina (EM2C)''

The aim of this project was to increase the computation performance using virtual chemistry approach in the YALES2 solver.

In order to reach this goal three test cases where identified:

- 1D laminar premixed flame (methane / air combustion with carbon monoxide prediction)

- 2D laminar premixed bunsen flame (methane / air combustion with carbon monoxide prediction)

- 3D two phase and turbulent flame (nheptane / air combustion with nitrogen monoxide prediction)

Several ways were explored:

- Profiling of reactive simulations when using Virtual Chemistry

- Effect of redundant species transport

- Effect of the size and the numbers of jacobian matrix to compute and solve

- Effect of the correction functions smoothing

Conclusions of the study are:

- String trimming and concatenation heavily affect computing performances

- Redundant species transport and source terms computations has a minor impact on performances

[[media:ecfd3_final_project19.pdf | Final presentation of project #19]]

=== Project #20: Stiff complex fluid simulation with YALES2 ===
''Sam Whitmore, Yves Dubief, M2CE, University of Vermont''

The objective was to simulate (1) ionized gases and (2) polymer solutions in flows using YALES2. Both problems are challenging owing to their stiff thermodynamics (1) or polymer dynamics (2). Significant gains were achieved in the implementation of the respective models thanks to the stiff integrator library CVODE. The plasma flow demonstrated an increase in time step of two orders of magnitude compared to previous implementation of the plasma chemistry in the variable density solver. Polymer models are notoriously prone to numerical instability. Again the use of CVODE showed equivalent if not superior stability of the solution at a fraction of the cost of commonly employed algorithms designed to address the stiffness of the problem.

[[media:ecfd3_final_project20.pdf | Final presentation of project #20]]

=== Project #21: AVBP Dense Gases ===

''Paolo ERRANTE (LMFA), Alexis GIAUQUE (LMFA), Christophe CORRE (LMFA)''

The simulation of dense gas flows using AVBP currently relies on the Martin-Hou Equation of State (EoS) to obtain the thermodynamic variables in each grid cell from the local value of density (or specific volume v) and internal energy derived from the conservative variables. The project develops an alternative approach where thermodynamic quantities in each cell are derived from a (given) set of tabulated thermodynamic states (Look-up Table or LuT). In order to preserve flow physics, the interpolation process in the LuT tables must be performed in a consistent way (a simple bilinear interpolation on v and T for each thermodynamic variable is not sufficient). Describing Helmholtz free energy f(v,T) with a bi-quintic Hermitian polynomial function in each cell of the LuT allows to ensure a consistent interpolation process (since all thermodynamic variables are obtained by differentiating the polynomial function). During the workshop the functions needed to perform the consistent interpolation have been implemented in the real gas module. Short-term perspectives are completing the implementation, validating the development on some test-cases previously computed using MAH EoS and optimizing the implementation (in particular the strategy used to identify the position in the LuT of each local grid state).

[[media:ecfd3_final_project21.pdf | Final presentation of project #21]]

=== Project #22: Numerical prediction of wind turbine wakes using AMR ===
S. Zeol (UMONS)i, P. Bénard (CORIA), G. Balarac (LEGI), L. Bricteux (UMONS)

The project considered here demonstrates the feasibility of the use of an adaptive mesh refinement method in the Eulerian finite volume code YALES2 for wind turbine wakes prediction.
The objective is to determinate the more effective methodology to adapt the mesh based on appropriate criterion.
We consider two methods : one for statistically steady flows based and one for purely unsteady flows (e.g. turbine with yaw, wind turbine with strong turbulence, inducing wake meandering)
Preliminary results were obtained on a testcase for which wind tunnel data are available: the NTNU blind test 1.
The static adaptation method applied on this case produced promising results and should eventually reduce the computational cost of this kind of simulations.
The dynamic adaptation method has been elaborated and some tests were performed to find the best adaptivity parameters.
The next step is to fully validate the methodology and consider then a more challenging test case with yaw adaptation.

Ecfd:ecfd 3rd edition

2020-01-31T10:59:30Z

Abarge: /* Project #7: Modélisation de parois pour la simulation des grandes échelles */

{{DISPLAYTITLE: ECFD workshop, 3rd edition, 2020}}
__NOTOC__

== Sponsors ==

[[File:ecfd3_sponsors.png|center|frameless|800px]]

== Participants ==

[[File:ecfd3_participants.png|center|frameless|1000px]]

[[File:lecfd3_participants_photo.jpg|center|frameless|1000px]]

== Flyer ==

* [[media:ecfd3_flyer.pdf | Flyer]]

== Presentations ==

* [[media:ecfd3_intro.pdf | Introduction workshop]]
* [[media:ecfd3_intro_genci.pdf | Introduction GENCI]]
* [[media:ecfd3_avbp_roadmap_HPC.pdf | Roadmap AVBP (HPC)]]
* [[media:ecfd3_yales2_roadmap.pdf | Roadmap YALES2]]

== Booklet ==

* [[media:ecfd3_booklet_template.zip | Template]]

== Project achievements ==

=== Project #1: Hackathon GENCI/ATOS/AMD/CERFACS on AVBP ===

''C. Piechurski (GENCI), S. Jauré (ATOS), B. Pajot (ATOS), P.-A. Harraud (AMD), P. Mohanamuraly (CERFACS), G. Staffelbach (CERFACS), J. Legaux (CERFACS)''

We ported the AVBP solver to the AMD Rome system available at GENCI -TGCC ( IRENE Joliot Curie).
Characterisation of the application on the architecture showed a 1/3 performance dependency to bandwidth and 2/3 to compute.
Strong scaling performance up to 130k cores was measured with openmpi and provided an acceleration of 75% without optimisations.
Weak scaling up to 32k MPI ranks suggests that decimation of the processes by a factor 2 improves computational efficiency by up to 30%.
This suggests a trade off between mpi imbalance and decimation is possible if imbalance is higher than 30% to improve time to solution.

Currently Openmpi offers the best perfofrmance, intelmpi is still a bit unstable.

During the Hackathon we also introduced colour based cache blocking using ColPack in the code in order to use OpenMP without critical sections.
On a 2x18 core Skylake processor the new implementation offered similar speedup using full threading versus full MPI with the best trade off being 4 MPI and 9 threads per MPI.
On AMD Rome, Full threading did not offer much acceleration and needs to be inversigated but 8 MPI and 16 threads per MPI seem quite promising.

[[media:ecfd3_final_project1.pdf | Final presentation of project #1]]

=== Project #2: Hackathon GENCI/ATOS/AMD/CORIA on YALES2 ===
''C. Piechurski (GENCI), S. Jauré (ATOS), P.-A. Harraud (AMD), P. Mohanamuraly (CERFACS), G.Lartigue (CORIA), F. Gava (CORIA), K. Bioche (CORIA), P. Begou (LEGI)''

[[media:ecfd3_final_project2.pdf | Final presentation of project #2]]

=== Project #3: Implementation of a secondary atomization model in YALES2 ===

''C. G. Guillamon (Safran Tech), L .Voivenel (Safran Tech), R. Mercier (Safran Tech)''

In Lagrangian simulations, droplets are transported following a ballistic motion in an eulerian mesh. For non-reactive environments, droplets might undergo secondary atomization due to the aerodynamic interaction. In this work, we implement in YALES2 a breakup model known as Taylor-Analogy Breakup (TAB). This model is based on the analogy between a droplet and a second-order mechanical system, hence making possible to determine the breakup behaviour by means of Newton's second law.

Another model, the stochastic breakup model by Gorokhovski, is also suggested for future work and will be implemented in YALES2.

[[media:ecfd3_final_project3.pdf | Final presentation of project #3]]

=== Project #4: Conservative Heat Transfers in the the Accurate Conservative Level-Set framework ===

''François Pecquery (ARIANE GROUP), Mélody Cailler (SAFRAN TECH), Romain Janodet (SAFRAN TECH/CORIA) and Vincent Moureau (CORIA)''

Objectives of the project was to introduce conservative heat transfers in the Accurate Conservative Level-Set framework to be able to describe heat transfers and liquid dynamics in an accurate, robust and conservative manner. A Multi-Phase Transport solver is introduced relying on the conserving and level-set coherent transport of the temperature. The solution is to use the fluxes of a phase indicator that may be sharp, contrarily to the level-set. The new solver was used on a simplified test case where a liquid droplet is transported in a temperature stratified environment. Results show promising capabilities of the new framework. Next work include improvement of the transport equation stability, and of the jump condition at the interface.

[[media:ecfd3_final_project4.pdf | Final presentation of project #4]]

=== Project #5: Jet-in-crossflow par une méthode d’interface diffuse ===

''T. Laroche, N. Odier, B. Cuenot (CERFACS). In collaboration with M. Pelletier, T. Schmitt, S. Ducruix (EM2C)''

In the context of fuel injection in an aircraft engine, liquid fuel is injected through a swirler, and sheared by a high-speed oxyder which destabilizes the liquid interface. This interaction induces liquid ligaments, which break up into large droplets (primary atomization), and then themselves break into small droplets (secondary atomization)
This project deals with the implementation of a diffuse-interface method in the massively parallel solver AVBP to represent the liquid interface destabilization during primary atomization for compressible applications. This methodology is found to be very efficient, however a control of the interface diffusion is mandatory as soon as convective effects are added. During this workshop, the methodology proposed by Chiodi and Desjardins ( ''A reformulation of the conservative level set reinitialization equation for accurate and robust simulation of complex multiphase flows'', JCP 2017) to control the interface thickness has been implemented in AVBP, and is currently under validation on a periodic liquid jet with surface tension effects.

[[media:ecfd3_final_project5.pdf | Final presentation of project #5]]

=== Project #6: Accurate numerical predicti􏴇on of vorti􏴇cal flows using AMR ===

We try to demonstrate that Eulerian method YALES2 using AMR can do a very good job to capture complex vortical flows at moderate Re=10k
Here we use an AMR strategy based on vorticity. We investigate the problem of vortex ring collision. We have a gain of 1000 on the numbers of elements compared
to a non adaptative approach. We are able to capture the transition from a very simple laminar flow to a complex turbulent flow.

[[media:ecfd3_final_project6.pdf | Final presentation of project #6]]

=== Project #7: Modélisation de parois pour la simulation des grandes échelles ===

[[media:ecfd3_final_project7.pdf | Final presentation of project #7]]

We ran simulations to benchmark the Dynamic Slip Wall method from (Bose & Moin, PoF, 2014) that we implemented in YALES2. The performances of the method have been compared with those from the classic Log-Law and the method from (Duprat et al., PoF, 2011) on the standard cases of channel flow and periodic hills. The results from the Dynamic Slip wall showed a satisfying efficiency although its precision stays comparable to the method from Duprat et al. Also, we set up the non-stationary test case of oscillating channel flow to enrich the benchmarking with the above-mentioned methods. Finally, we started to work on the implementation of a new approach proposed by M. Gorokhovski, tests are in progress.

=== Project #8: Accurate numerical simulation of contact lines with dynamic mesh adaptation ===
''S. Pertant (LEGI), G. Ghigliotti (LEGI), G. Balarac (LEGI)''

The main objective of this project was to develop a methodology to simulate contact lines on unstructured meshes. We especially wanted to get rid of mesh influence on contact line movement when the flow is driven by surface tension and the contact line close to its equilibrium position. A slight modification in the Ghost Fluid Method to apply the pressure jump has been tested and seems promising. The pressure gradient at contact line is indeed less sensitive to mesh elements for high density ratios. Furthermore, dynamic mesh adaptation has been used to simulate a 2D vapour bubble lying on a wall. Due to gravity, the two contact lines are receding until their merging and the bubble departure. The mesh remains fine to capture the contact line dynamics. As a future work, we plan to perform mesh adaptation on 3D contact line cases and to include additional physics such as contact angle imposition (already implemented but not used yet with mesh adaptation).

[[media:ecfd3_final_project8.pdf | Final presentation of project #8]]

=== Project #9: Remeshed particle method at high Schmidt and Reynolds number ===

''S. Santoso (LJK), J.-B. Lagaert (Math Orsay), G.Balarac (LEGI)''

We study the advection of a scalar function in turbulent flows with a multimesh method. The finite volume method is used to solve Navier-Stokes equations on an unstructured mesh (YALES2). The advection equation is solved with remeshed particle method on a cartesian mesh. In the context of parallel computing, we face a very unbalanced problem since a large number of particles are created in a very fine meshed zone. Our strategy to load-balance the problem is to give a weight to every element group which is equal to the density of particle.

[[media:ecfd3_final_project9.pdf | Final presentation of project #9]]

=== Project #10: Adaptive mesh refinement for turbulent premixed combustion ===
''W. Agostinelli, O. Dounia, , T. Jaravel, O. Vermorel

The objective of the project was to evaluate the potential of adaptive mesh refinement (AMR) for premixed combustion in unsteady systems. Three target cases were identified: a semi-vented deflagration with laminar to turbulent transition, a planar detonation wave, and a bluff-body stabilized burner subjected to thermoacoustic oscillations. The simulations were performed with AVBP and coupled to the AMR implementation of YALES2. Several metrics and remeshing criterions were developed to identify and correctly resolve both the combustion wave front and the turbulent flow. The comparison of numerical results with reference simulations showed that the main features of the physics could be recovered with a significant speed-up in term of computational cost.

[[media:ecfd3_final_project10.pdf | Final presentation of project #10]]

=== Project #11: Multiphysics coupling for wind turbine wake modeling ===

''F.Houtin-Mongrolle (CORIA), B. Duboc (SGRE), P. Benard (CORIA)''

The goal of this project was to evaluate the coupling of YALES2 (flow solver) and BHawC(Aero-Servo-Elastic solver).

[[media:ecfd3_final_project11.pdf | Final presentation of project #11]]

=== Project #12: Stability of a semi-implicit compressible cavitation solver ===

''H. Garg (LEGI), G. Ghigliotti (LEGI) and G. Balarac (LEGI)''

The compressible cavitation solver is used to simulate cavitation inception in an initially liquid flow behind an obstacle.
This solver is based on the implicit compressible solver, that has been modified to include a « barotropic » pressure-density relationship playing the role of an equation of state independent from the temperature.
While this strategy has proven to be effective for DNS simulations of the implosion of vapour bubbles, the simulation of cavitation inception in an initially liquid flow was leading to strong instabilities in the simulation shortly after the appearence of vapour.
The test case chosen is a flow behind a 2D cylinder.
The analysis of the results has shown that instabilities were correlated with very low (and even unphysically negative) values of the pressure, that were triggering negative density values leading to code instability.
Using limiters to ensure a positive pressure and a density within the range of the equation of state improved the stability and allowed to perform a preliminary simulation of a cavitating flow behind an obstacle.
Ultimately instabilities appear anyways, so that the will look to the spatial discretisation schemes.

[[media:ecfd3_final_project12.pdf | Final presentation of project #12]]

=== Project #13: Validations and comparisons of Diffuse / Sharp interface methods in a structured DNS solver (Titan) ===
''V. Boniou (EM2C), J.M. Dupays (EM2C), M. Pelletier (EM2C), T. Schmitt (EM2C), A. Vié (EM2C)

The project aimed at using academic test cases to compare the sharp (incompressible) and diffuse (compressible) models. In particular, the test case of an inviscid initially elliptical oscillating droplet has been carried out.
The solvers features are the following:

- incompressible VOF solver (sharp): Numerical Method: Projection Method, Interface reconstruction: VOF, Surface tension: CSF

- compressible multifluid solver (diffuse): Advection scheme: MUSCL + RK2 + minmod limiter, Surface tension: CSF.

The source term is integrated with operator-splitting, and the curvature computation relies on a 2nd-order differentiation of the liquid volume fraction, which is previously smooth by filtering.
This test case showed good agreement on the oscillation period, while exhibiting a slight numerical diffusion in the incompressible case and a strong numerical diffusion in the compressible case.
In the compressible case, the use of higher-order splitting (Strang [SIAM Num. An. 1968]) has been tested, yielding no noticeable improvement. Reduction of the number of filtering iterations on the liquid volume fraction provides a slight improvement, which may indicate that a better curvature computation could participate to reduce the numerical diffusion.

[[media:ecfd3_final_project13.pdf | Final presentation of project #13]]

=== Project #14: High Order Framework ===
''M. Bernard (LEGI), G. Lartigue (CORIA), G. Balarac (LEGI), V. Moureau (CORIA)''

Aim of this project is to extend the high order framework (HOF) in Yales2.
As a reminder, the HOF permits to reconstruct a point-wise quantity from the volume-averaged one, arising from classical Finite-Volume schemes, and thus to improve spatial accuracy of numerical schemes.

During the ECFD workshop #3, a dedicated solver has been created, the high order solver (hos), duplicated from the incompressible solver (ics).
We started activating the HOF ingredients previously developed, starting from velocity field advancement.
Development is still in progress, but the static Taylor-Green vortices test-case has been investigated in order to see the early improvement.

[[media:ecfd3_final_project14.pdf | Final presentation of project #14]]

=== Project #15: Validation of a fluid structure interaction case with the coupling ALE/SMS ===
''T. Fabbri (LEGI), G. Lartigue (CORIA), G. Balarac (LEGI), V. Moureau (CORIA)''

The objective of this project was the validation of the Turek(2006) benchmark for fluid structure case.
The Structural Mechanics Solver (SMS) was already existing before the workshop, as the coupling with the Arbitrary-Lagrangian Eulerian solver.
However, the results were not in agreement with the case. The data compared here are the flexible part tip displacement, but also the drag and the lift integrated
on the cylinder and the flexible part.
The pure structure test cases were validated, but the forces computed for the pure fluid test cases were not satisfying.
The work of this week was then to improve the viscous shear computation, which implies the wall normal gradient computation.

[[media:ecfd3_final_project15.pdf | Final presentation of project #15]]

=== Project #16: Development of a RANS solver in YALES2 ===
''G. Sahut (LEGI), G. Balarac (LEGI), V. Moureau (CORIA), G. Lartigue (CORIA), P. Bénard (CORIA), A. Grenouilloux (CORIA)''

While the accuracy of LES usually approaches the one of DNS, LES are still too time-consuming for daily use in industrial applications. In this context, we started the development of a RANS solver in YALES2. We are first only interested in the steady state of the solution. In order to remove the CFL constraint, we developed, implemented and validated an implicit projection method for the resolution of the Navier-Stokes equations without turbulence models. The method is based on the implicitation of the velocity predictor ; the Poisson equation and the correction step of the velocity are then solved and applied as in the explicit incompressible solver. We validated the method on a stationary 2D Poiseuille flow with periodic boundary conditions: the simulation runs fine for CFL and Fourier numbers which are inaccessible with the explicit incompressible solver. The advection-diffusion equation for scalars has also been implicited and will be used to add turbulence models to the new implicit incompressible solver developped during this Workshop. More complex boundary conditions will also be addressed in a near future.

[[media:ecfd3_final_project16.pdf | Final presentation of project #16]]

=== Project #17: IMPLEMENTATION OF A COLD PLASMA MODEL IN YALES2 ===

''J.-M. Orlac'h (EM2C), G. Lartigue (CORIA), B. Fiorina (EM2C)''

The objective of this project was to further develop the cold plasma solver in YALES2 in order to accurately model silane nanodusty discharges. The electron temperature equation has been implemented successfully and validated against a reference plasma code. In a second step, a detailed electron kinetics has been implemented in YALES2 in order to couple the electron temperature with the charged species mass fractions. The user can now define a list of reactions whose rates depend on the electron temperature. These improvements open the path to the simulation of nanoparticle production in silane discharges using a Lagrangian description for the nanoparticles.

[[media:ecfd3_final_project17.pdf | Final presentation of project #17]]

=== Project #18: L’Evaporo O Maıtre ===

[[media:ecfd3_final_project18.pdf | Final presentation of project #18]]

=== Project #19: The Clone Wars ===
''H. Maldonado Colman (EM2C), C. Nguyen Van (EM2C - Safran-Tech), R. Mercier (Safran-Tech), B. Fiorina (EM2C)''

The aim of this project was to increase the computation performance using virtual chemistry approach in the YALES2 solver.

In order to reach this goal three test cases where identified:

- 1D laminar premixed flame (methane / air combustion with carbon monoxide prediction)

- 2D laminar premixed bunsen flame (methane / air combustion with carbon monoxide prediction)

- 3D two phase and turbulent flame (nheptane / air combustion with nitrogen monoxide prediction)

Several ways were explored:

- Profiling of reactive simulations when using Virtual Chemistry

- Effect of redundant species transport

- Effect of the size and the numbers of jacobian matrix to compute and solve

- Effect of the correction functions smoothing

Conclusions of the study are:

- String trimming and concatenation heavily affect computing performances

- Redundant species transport and source terms computations has a minor impact on performances

[[media:ecfd3_final_project19.pdf | Final presentation of project #19]]

=== Project #20: Stiff complex fluid simulation with YALES2 ===
''Sam Whitmore, Yves Dubief, M2CE, University of Vermont''

The objective was to simulate (1) ionized gases and (2) polymer solutions in flows using YALES2. Both problems are challenging owing to their stiff thermodynamics (1) or polymer dynamics (2). Significant gains were achieved in the implementation of the respective models thanks to the stiff integrator library CVODE. The plasma flow demonstrated an increase in time step of two orders of magnitude compared to previous implementation of the plasma chemistry in the variable density solver. Polymer models are notoriously prone to numerical instability. Again the use of CVODE showed equivalent if not superior stability of the solution at a fraction of the cost of commonly employed algorithms designed to address the stiffness of the problem.

[[media:ecfd3_final_project20.pdf | Final presentation of project #20]]

=== Project #21: AVBP Dense Gases ===

''Paolo ERRANTE (LMFA), Alexis GIAUQUE (LMFA), Christophe CORRE (LMFA)''

The simulation of dense gas flows using AVBP currently relies on the Martin-Hou Equation of State (EoS) to obtain the thermodynamic variables in each grid cell from the local value of density (or specific volume v) and internal energy derived from the conservative variables. The project develops an alternative approach where thermodynamic quantities in each cell are derived from a (given) set of tabulated thermodynamic states (Look-up Table or LuT). In order to preserve flow physics, the interpolation process in the LuT tables must be performed in a consistent way (a simple bilinear interpolation on v and T for each thermodynamic variable is not sufficient). Describing Helmholtz free energy f(v,T) with a bi-quintic Hermitian polynomial function in each cell of the LuT allows to ensure a consistent interpolation process (since all thermodynamic variables are obtained by differentiating the polynomial function). During the workshop the functions needed to perform the consistent interpolation have been implemented in the real gas module. Short-term perspectives are completing the implementation, validating the development on some test-cases previously computed using MAH EoS and optimizing the implementation (in particular the strategy used to identify the position in the LuT of each local grid state).

[[media:ecfd3_final_project21.pdf | Final presentation of project #21]]

=== Project #22: Numerical prediction of wind turbine wakes using AMR ===
S. Zeol (UMONS)i, P. Bénard (CORIA), G. Balarac (LEGI), L. Bricteux (UMONS)

The project considered here demonstrates the feasibility of the use of an adaptive mesh refinement method in the Eulerian finite volume code YALES2 for wind turbine wakes prediction.
The objective is to determinate the more effective methodology to adapt the mesh based on appropriate criterion.
We consider two methods : one for statistically steady flows based and one for purely unsteady flows (e.g. turbine with yaw, wind turbine with strong turbulence, inducing wake meandering)
Preliminary results were obtained on a testcase for which wind tunnel data are available: the NTNU blind test 1.
The static adaptation method applied on this case produced promising results and should eventually reduce the computational cost of this kind of simulations.
The dynamic adaptation method has been elaborated and some tests were performed to find the best adaptivity parameters.
The next step is to fully validate the methodology and consider then a more challenging test case with yaw adaptation.