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Gilles Bernard-Michel Benjamin Cariteau

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):

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Gilles Bernard-Michel Benjamin Cariteau

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  1. Id 165 : HELIUM RELEASE IN A CLOSED ENCLOSURE: COMPARISONS BETWEEN SIMPLE MODELS, CFD CALCULATIONS AND EXPERIMENTAL RESULTS Gilles Bernard-Michel Benjamin Cariteau

  2. Context and objectives • 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/

  3. 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. Modeling stategy • 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).

  5. Conservation Equations

  6. 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. Qualitative results

  8. Reversal vortex Reversal vortex is observed : => Confirms the theory predicting coexistence of stratification and homogeneous layer.

  9. Time concentration profile – 5mm case

  10. Time concentration profile – 20mm case

  11. Vertical concentration profile – 20mm case • Codes results are more diffusive : • More stratification • Almost no homogeneous layer at the top.

  12. Conclusions and perpectives • 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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