Transcript HELIUM RELEASE IN A CLOSED ENCLOSURE: COMPARISONS BETWEEN SIMPLE MODELS, CFD CALCULATIONS AND EXPERIMENTAL RESULTS

08-PANH-06
Id 165 : HELIUM RELEASE IN A CLOSED ENCLOSURE:
COMPARISONS BETWEEN SIMPLE MODELS, CFD CALCULATIONS
AND EXPERIMENTAL RESULTS
Gilles Bernard-Michel
Benjamin Cariteau
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Réunion : Avancement DIMITRHY
Tâche II : Mitigation des ATEX… Sous-tâche II.3
Lieu: Carrières sous Poissy
date : 23 juin 2011
Context and objectives
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• A benchmark (Air liquide, INERIS, PSA, CEA):
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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 :
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Turbulence : K-epsilon, LES, laminar, for what injection flux and diameter etc…
Compressibility : Boussinesq, Low Mach, Fully compressible ?
• Numerical discretization validation :
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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 :
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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/
2
Réunion : Avancement DIMITRHY
Tâche II : Mitigation des ATEX… Sous-tâche II.3
Lieu: Carrières sous Poissy
date : 23 juin 2011
Experimental set-up
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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.
3
Réunion : Avancement DIMITRHY
Tâche II : Mitigation des ATEX… Sous-tâche II.3
Lieu: Carrières sous Poissy
date : 23 juin 2011
Modeling stategy
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• Non costy calculations
=> geometrical
simplifications
•Highly converged
calculations => EF order 3,
and BDF2 time
discretization scheme.
• L.E.S for turbulence
• 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).
4
Réunion : Avancement DIMITRHY
Tâche II : Mitigation des ATEX… Sous-tâche II.3
Lieu: Carrières sous Poissy
date : 23 juin 2011
Conservation Equations
08-PANH-06
5
Réunion : Avancement DIMITRHY
Tâche II : Mitigation des ATEX… Sous-tâche II.3
Lieu: Carrières sous Poissy
date : 23 juin 2011
Discretization Grids
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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.
6
Réunion : Avancement DIMITRHY
Tâche II : Mitigation des ATEX… Sous-tâche II.3
Lieu: Carrières sous Poissy
date : 23 juin 2011
Qualitative results
08-PANH-06
7
Réunion : Avancement DIMITRHY
Tâche II : Mitigation des ATEX… Sous-tâche II.3
Lieu: Carrières sous Poissy
date : 23 juin 2011
Reversal vortex
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Reversal vortex is
observed :
=> Confirms the
theory predicting
coexistence of
stratification and
homogeneous layer.
8
Réunion : Avancement DIMITRHY
Tâche II : Mitigation des ATEX… Sous-tâche II.3
Lieu: Carrières sous Poissy
date : 23 juin 2011
Time concentration profile – 5mm case
08-PANH-06
9
Réunion : Avancement DIMITRHY
Tâche II : Mitigation des ATEX… Sous-tâche II.3
Lieu: Carrières sous Poissy
date : 23 juin 2011
Time concentration profile – 20mm case
08-PANH-06
10
Réunion : Avancement DIMITRHY
Tâche II : Mitigation des ATEX… Sous-tâche II.3
Lieu: Carrières sous Poissy
date : 23 juin 2011
Vertical concentration profile – 20mm case
08-PANH-06
Codes results are
more diffusive :
- More stratification
- Almost no
homogeneous layer
at the top.
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Réunion : Avancement DIMITRHY
Tâche II : Mitigation des ATEX… Sous-tâche II.3
Lieu: Carrières sous Poissy
date : 23 juin 2011
Conclusions and perpectives
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• 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
• 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.
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Réunion : Avancement DIMITRHY
Tâche II : Mitigation des ATEX… Sous-tâche II.3
Lieu: Carrières sous Poissy
date : 23 juin 2011