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[ID 204] Evaluation of ADREA-HF LES against Hydrogen release dispersion

[ID 204] Evaluation of ADREA-HF LES against Hydrogen release dispersion. Mr. Nektarios Koutsourakis 1,2 Dr. Alexander Venetsanos 2 Prof. John G. Bartzis 1 4th International Conference on Hydrogen Safety San Francisco, California, September 12-14, 2011 1 University of West Macedonia Greece

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[ID 204] Evaluation of ADREA-HF LES against Hydrogen release dispersion

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  1. [ID 204] Evaluation of ADREA-HF LES against Hydrogen release dispersion Mr. Nektarios Koutsourakis1,2 Dr. Alexander Venetsanos2 Prof. John G. Bartzis1 4th International Conference on Hydrogen Safety San Francisco, California, September 12-14, 2011 1 University of West Macedonia Greece 2 NCSR “Demokritos” Greece ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  2. ADREA-HF CFD CODEConstantly developing • Latest additions: • LES (Large Eddy Simulation) • Parallel solver • Arbitrary number of species • Combustion • Back tracking • GUI pre and post processor (called EDes) • Advantages: • Robust, powerful and general • Specialization in environmental applications ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  3. ADREA-HF CFD CODEADREA specializes in dispersion applications ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  4. ADREA-HF CFD CODEGUI environment for pre and post processing ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  5. LARGE EDDY SIMULATIONBetween DNS and RANS • Navier-Stokes math. analysis: impossibly difficult • DNS: Fully-resolved NS • Cost Re2.75 (for wall-bounded flows  Re3.5) • RANS: Time-averaged NS • Fast, widely tested, usually accurate “enough” • LES: Spatially-filtered NS • Cost near wall: Re2.4 ! (at outer layer  Re0.5) • Converges to DNS. As in DNS, LES needs:a) averaging b) demanding boundary conditions • Suggested were RANS fails: transient, separated flow ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  6. ENERGY CASCADELES solves most of the turbulence ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  7. LES EQUATIONS AT ADREA-HFCompressible volume-filtered Navier-Stokes ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  8. LES EQUATIONS AT ADREA-HFAlternative subgrid model: RNG-LES ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  9. LES AT ADREA-HFNumerics • ADREA/SIMPLER algorithm • Solver: Parallel BiCGstab with parallel Schwarz preconditioner. Speedup with 2 CPUs up to 1.7 • Numerics: • Deferred correction central scheme for convection • Crank-Nicolson 2d order for time advancement • Linear upwind with VanLeer limiter for concentration • For more: • Venetsanos, A. G., E. Papanikolaou and J. G. Bartzis, 2010: The ADREA-HF CFD code for consequence assessment of hydrogen applications. Int. J. Hydrogen Energy, 35, 3908. ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  10. TEST CASEHySafe INERIS-6Cexperiment • 1g/s H2 for 240s • Jet 20mm • Room 3.78 * 7.2 * 2.88m ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  11. TEST CASE SETUPSimulation details • Standard Smagorinsky with Cs=0.1 • Total number of cells in the room: 130000 • CFLmax=0.3 • Minimum mesh resolution: 0.02*0.02*0.053 m • Simulation time in a workstation:15 days for the release phase (240s); dtav1= 0.0005s+ 2 days for the first 260s of the post-release phase ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  12. TEST CASE SETUPGeometry, sensors, part of the grid ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  13. RESULTSComparison with experiment Photo fromexperiment ADREALES ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  14. RESULTSVideo of the Hydrogen propagation ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  15. RESULTSConcentration contours animation ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  16. RESULTSComparison with sensors ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  17. DISCUSSIONSome remarks • In general very good agreement • High turbulence during release phase, only • Release overestimated, especially near source.Very difficult for CFD and for turbulence modelling to capture the physical processes next to the source • Diffusion underestimated (possible experimental asymmetry?) - improvement with better grid • Better agreement is prevented from experimental inaccuracies and numerical discrepancies ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  18. FURTHER EXAMINATION Cs value influence (release phase -coarse grid) Jet axis sensors Ceilingsensors Side wall sensors Sensor 16 Sensor 14 Sensor 13 Sensor 1 Sensor 4 Sensor 6 Sensor 7 Sensor 8 Sensor 9 Sensor 10 Sensor 12 ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  19. DISCUSSIONCs affects the results • Cs (SGS modelling in general) important near jet • At the ceiling, no Cs influence (buoyancy dominates) • Non-monotonic behaviour (increasing the Cs gives better results, but up to a limit) • Worst Cs by far: 0.2 ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  20. FURTHER EXAMINATIONC variances for each Cs C variance = mean (Ci’2) ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  21. DISCUSSIONA critical balance: resolved vs. SGS turbulence • As we go away from the jet, variance (and resolved turbulence intensity) drops • Two mechanisms compete:- Modelled SGS turbulence- Resolved turbulence (generally low if SGS is high) • With Cs=0.2, very high artificial viscosity causes more “laminar” flow and lower fluctuations ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  22. FURTHER EXAMINATIONEvaluation of RNG-LES (run not finished yet) ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  23. DISCUSSIONRNG LES seems to be an improvement • RNG LES provides in general better results • Improvement towards the right side for sensors both close to the jet (turbulent flow) and far from it (laminar flow). That was not the case by varying Cs • Resolved turbulence seems to decrease close to the jet and increase far from it • RNG LES is believed to better model the subgrid scales for both the turbulent and the laminar flow ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  24. CONCLUSIONS I Acceptable results and physical insight • LES results are good, given all numerical and experimental inaccuracies • Overestimation during release phase (close to jet) • Underestimation during diffusion phase (and far from jet) • Attempt to investigate the balance between resolved and SGS turbulence with parametric analysis of Cs • RNG LES seems to behave slightly better in both turbulent and laminar parts of the flow ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  25. CONCLUSIONS II LES is good, but not for everyday use • ADREA-HF has now tested LES in hydrogen release • LES can provide peak concentrations (good for flammable mixtures or for calculation of dosages) • LES can provide concentration statistics • LES many times more expensive than RANS • LES is not RANS++ ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

  26. THANK YOU Acknowledgements: Greek Scholarships Foundation, Municipality of Aghia Varvara ICHS 2011, #204 LES MODELLING OF HYDROGEN RELEASE AND ACCUMULATION WITHIN A NON-VENTILATED AMBIENT PRESSURE GARAGE USING THE ADREA-HF CFD CODE

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