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Id 165 : HELIUM RELEASE IN A CLOSED ENCLOSURE: COMPARISONS BETWEEN SIMPLE MODELS, CFD CALCULATIONS AND EXPERIMENTAL RESULTS. Gilles Bernard-Michel Benjamin Cariteau. Context and objectives. A benchmark (Air liquide, INERIS, PSA, CEA): - PowerPoint PPT Presentation
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1
08-PANH-06
Réunion : Avancement DIMITRHYTâche II : Mitigation des ATEX… Sous-tâche II.3Lieu: Carrières sous Poissy date : 23 juin 2011
Id 165 : HELIUM RELEASE IN A CLOSED ENCLOSURE: COMPARISONS BETWEEN SIMPLE MODELS, CFD CALCULATIONS
AND EXPERIMENTAL RESULTS
Id 165 : HELIUM RELEASE IN A CLOSED ENCLOSURE: COMPARISONS BETWEEN SIMPLE MODELS, CFD CALCULATIONS
AND EXPERIMENTAL RESULTS
Gilles Bernard-MichelBenjamin Cariteau
2
08-PANH-06
Réunion : Avancement DIMITRHYTâche II : Mitigation des ATEX… Sous-tâche II.3Lieu: Carrières sous Poissy date : 23 juin 2011
• A benchmark (Air liquide, INERIS, PSA, CEA): • This work takes place in a benchmark (Dimithry ANR project)• Code comparisons : FLUENT, FLACS, PHOENIX, CAST3M• CFD Vs experimental results comparisons (GAMELAN exp. Set-up).
• Physical model validation :• Turbulence : K-epsilon, LES, laminar, for what injection flux and diameter etc…• Compressibility : Boussinesq, Low Mach, Fully compressible ?
• Numerical discretization validation :• 1st or 2nd order time scheme ? • Explicite/ implicite, what terms of the equation ? For what purpose • Centered or upwind scheme for convection• Qualitiy of the mesh, convergence
• Simple models validation :• Worster and Hupper model works fine for 20 mm diameter injection with a
5Nl/min source, and under predict by a factor 2 helium concentrations fot a 5 mm diameter.
=> Need for a better understanding of the phenomenon which is not accessible with experiments/
Context and objectives
3
08-PANH-06
Réunion : Avancement DIMITRHYTâche II : Mitigation des ATEX… Sous-tâche II.3Lieu: Carrières sous Poissy date : 23 juin 2011
Experimental set-up
We only present two cases :-A closed box - 5mm diam. injection nozzle - 5Nl/min helium injection – jet/plume- A closed box - 20 mm diam. injection nozzle - 5 Nl/min helium injection – plume- High injection rate (jets) are not interesting because helium concentration is rapidely homogeneous.
4
08-PANH-06
Réunion : Avancement DIMITRHYTâche II : Mitigation des ATEX… Sous-tâche II.3Lieu: Carrières sous Poissy date : 23 juin 2011
• Non costy calculations => geometrical simplifications•Highly converged calculations => EF order 3, and BDF2 time discretization scheme.• L.E.S for turbulence
Modeling stategy
• Numerical cost reduction strategy :• Explicite convection• Constant time step by blocs• Algebraic projection method• => constant matrix for pressure discretization• Parallel direct solver for pressure equation• Parallel iterative solver for velocity, concentration equations(ILU0 precond, conjugate gradient).
5
08-PANH-06
Réunion : Avancement DIMITRHYTâche II : Mitigation des ATEX… Sous-tâche II.3Lieu: Carrières sous Poissy date : 23 juin 2011
Conservation Equations
6
08-PANH-06
Réunion : Avancement DIMITRHYTâche II : Mitigation des ATEX… Sous-tâche II.3Lieu: Carrières sous Poissy date : 23 juin 2011
Discretization Grids
time steps :• dt lower than 10 times CFL condition• dt around 5 ms for the 5mm injection• dt around 25 ms fot the 20mm injection.
7
08-PANH-06
Réunion : Avancement DIMITRHYTâche II : Mitigation des ATEX… Sous-tâche II.3Lieu: Carrières sous Poissy date : 23 juin 2011
Qualitative results
8
08-PANH-06
Réunion : Avancement DIMITRHYTâche II : Mitigation des ATEX… Sous-tâche II.3Lieu: Carrières sous Poissy date : 23 juin 2011
Reversal vortex is observed :
=> Confirms the theory predicting coexistence of stratification and homogeneous layer.
Reversal vortex
9
08-PANH-06
Réunion : Avancement DIMITRHYTâche II : Mitigation des ATEX… Sous-tâche II.3Lieu: Carrières sous Poissy date : 23 juin 2011
Time concentration profile – 5mm case
10
08-PANH-06
Réunion : Avancement DIMITRHYTâche II : Mitigation des ATEX… Sous-tâche II.3Lieu: Carrières sous Poissy date : 23 juin 2011
Time concentration profile – 20mm case
11
08-PANH-06
Réunion : Avancement DIMITRHYTâche II : Mitigation des ATEX… Sous-tâche II.3Lieu: Carrières sous Poissy date : 23 juin 2011
Codes results are more diffusive :- More stratification- Almost no homogeneous layer at the top.
Vertical concentration profile – 20mm case
12
08-PANH-06
Réunion : Avancement DIMITRHYTâche II : Mitigation des ATEX… Sous-tâche II.3Lieu: Carrières sous Poissy date : 23 juin 2011
• The model is accurate enough :• To predict concentration maxima better than 10% and
consequently the problems with Worster an Hupper model for the 5mm low injection rate case.
• To predict the reversal vortex• To predict correct concentration profiles
Conclusions and perpectives
• We will go for 3D modeling :• Discretization scheme and grids are validated• Solvers are fast enough to move to 3D• We expect to model correctly enough the jet to understand
what can be improved in the Worster and Hupper model.
