1. CFD Modeling for Helium Releases in a Private Garage without Forced Ventilation Papanikolaou E. A. Venetsanos A. G. NCSR "DEMOKRITOS" Institute of Nuclear Technology & Radiation Protection Environmental Research Laboratory Athens, GREECE venets@ipta.demokritos.gr NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY

2. Summary Scope: Evaluation of CFD ADREA-HF code capability to assess possible hazards posed by H 2 releases in confined spaces Experimental description Methodology Computational domain and grid Mathematical formulation Initial and boundary conditions Details of numerical solution Results of simulations Conclusions Future plans NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY

3. Scope NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Safe future H2 based society Safe use or storage of H2 systems inside buildings CFD models for assessment of hazards by H2 releases in confined spaces

4. Scope NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Evaluation of CFD ADREA-HF code capability to assess such scenarios

5. Experimental Description Swain et.al. (1998) Single car garage and sensors location NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Vehicle and leak location 7.200 Lt/hr Helium for 2 hours

6. Experimental Description Swain et.al. (1998) NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Case 1: 2.5 inches (6.35 cm) top and bottom door vents Single car garage and sensors location Vehicle and leak location 7.200 Lt/hr Helium for 2 hours

7. Experimental Description Swain et.al. (1998) NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Case 2: 9.5 inches (24.13 cm) top and bottom door vents Single car garage and sensors location Vehicle and leak location 7.200 Lt/hr Helium for 2 hours

8. Experimental Description Swain et.al. (1998) NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Case 3: 19.5 inches (24.13 cm) top and bottom door vents Single car garage and sensors location Vehicle and leak location 7.200 Lt/hr Helium for 2 hours

9. Methodology I. Computational Domain & Grid Domain extends beyond garage boundary NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Assumption of x-z plane symmetry due to geometry of facility and location of leak

10. Methodology I. Computational Domain & Grid NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Sensors located at the same side given the symmetry assumption Domain extends beyond garage boundary

11. Methodology I. Computational Domain & Grid 3-D Cartesian grid Grid refinement close to vents, source, walls Max. grid expansion ratio: 1.2 Min. grid expansion ratio: 0.84 Classification of cells into fully active, inactive and partially active DELTA_B Code for geometrical pre- processing NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Grid characteristicsCase 1Case 2Case 3 Grid dimensions88  26  4888  26  5088  26  44 Number of active cells101.887106.21893.552 Min. and Max. cell size in z- direction (m) 0.04 close to source 0.512 at domain’s top 0.038 close to source 0.513 at domain’s top 0.065 close to source 0.516 at domain’s top Min. and Max. cell size in x-direction (m) 0.02 close to door 0.92 at domain’s end Minimum and Maximum cell size in y-direction (m) 0.1 close to source and symmetry plane 0.401 at domain’s beginning Grid characteristicsCase 1Case 2Case 3 Grid dimensions88  26  4888  26  5088  26  44 Number of active cells101.887106.21893.552 Min. and Max. cell size in z- direction (m) 0.04 close to source 0.512 at domain’s top 0.038 close to source 0.513 at domain’s top 0.065 close to source 0.516 at domain’s top Min. and Max. cell size in x-direction (m) 0.02 close to door 0.92 at domain’s end Minimum and Maximum cell size in y-direction (m) 0.1 close to source and symmetry plane 0.401 at domain’s beginning Grid characteristicsCase 1Case 2Case 3 Grid dimensions88  26  4888  26  5088  26  44 Number of active cells101.887106.21893.552 Min. and Max. cell size in z- direction (m) 0.04 close to source 0.512 at domain’s top 0.038 close to source 0.513 at domain’s top 0.065 close to source 0.516 at domain’s top Min. and Max. cell size in x-direction (m) 0.02 close to door 0.92 at domain’s end Minimum and Maximum cell size in y-direction (m) 0.1 close to source and symmetry plane 0.401 at domain’s beginning

12. Methodology II. Mathematical Formulation 3-D transient, fully compressible conservation equations Mixture mass Mixture momentum Helium mass fraction Mixture density and mass fractions and Component densities through ideal gas law NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY

13. Methodology II. Mathematical Formulation (continued) Standard k-ε model for turbulence Turbulent viscosity Turbulent kinetic energy, k Volumetric production rate of k by shear forces G and buoyancy production (destruction) term G B Dissipation rate of turbulent kinetic energy, ε NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY

14. Methodology II. Mathematical Formulation (continued) NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Variables to be calculated Component velocities u, v, w He mass fraction, q 1 Pressure, P Turbulent kinetic energy, k Dissipation rate of turbulent kinetic energy, ε Not calculated variable but supplied by the initialization data Temperature, T

15. Methodology III. Initial & Boundary Conditions Initial Conditions Zero wind velocity with no turbulence Temperature of 293.15 K and hydrostatic pressure Boundary Conditions applied to: 1 free building surface as the Helium source 28 solid building surfaces 1 solid domain surface (the ground) 5 free domain surfaces NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY

16. Methodology III. Initial & Boundary Conditions (continued) NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Inflow boundary conditions at the source

17. Methodology III. Initial & Boundary Conditions (continued) NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Wall function for velocity: Wall function for k: Wall function for ε:

18. Methodology III. Initial & Boundary Conditions (continued) NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Wall function for velocity: Wall function for k: Wall function for ε: The wall function for velocity forms the basis of the empirical relationship to describe the shape of the wall boundary layer in non-dimensional terms

19. Methodology III. Initial & Boundary Conditions (continued) NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Wall function for velocity: Wall function for k: Wall function for ε: The wall function for velocity forms the basis of the empirical relationship to describe the shape of the wall boundary layer in non-dimensional terms

20. Methodology III. Initial & Boundary Conditions (continued) NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Wall function for velocity: Wall function for k: Wall function for ε:

21. Methodology III. Initial & Boundary Conditions (continued) NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY *1 function of the flow direction *2 normal velocity obtained from continuity equation *1 function of the flow direction

22. Details of Numerical Solution NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY CFD Code ADREA-HF for simulation Control volume discretization method, staggered grid arrangement for velocities First order fully implicit scheme for time integration First order upwind scheme for discretization of the convective terms Automatic time step selection based on convergence error Initial time step: 10 -3 seconds Maximum permitted time step: 10 -1 seconds Intel ® Xeon TM CPU 3.60GHz with Windows operating system Calculations performed for real time of 7.200 seconds

23. Results: Case 1 (2.5 inches) Outputs of simulation versus experimental data at sensor locations NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Good agreement for sensors 2 and 3 (upper vents) Overestimation for sensors 1 and 4 (lower vents) Underestimation of the predicted concentration difference between top and lower sensors

24. Results: Case 1 (continued) Bottom vent provides a flow of fresh air, flowing under the vehicle Upper vent provides an exit of the low density gas mixture, near the ceiling The combustible gas cloud is located under the vehicle, near the source and extends in the z-direction in front of it The rest of the garage gas remained leaner than the lean limit of combustion for Hydrogen Flow pattern has reached steady state conditions at least at 3.600 seconds NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY

25. Results: Case 2 (9.5 inches) Outputs of simulation versus experimental data at sensor locations NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY The vent sizes are almost 4 times broader than in Case 1 The predicted He concentrations are in satisfactory agreement with the experimental data for all sensors

26. Results: Case 2 (continued) The exiting gas mixture has now a wider column-like shape which broadens with height Most of the garage gas remained leaner than the lean limit of combustion for Hydrogen (4.1%) Flow pattern has reached steady state conditions at least at 3.600 seconds NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY

27. Results: Case 3 (19.5 inches) Outputs of simulation versus experimental data at sensor locations NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Underestimation for sensors 1, 2 and 3 Small over prediction for sensor 4 The predicted natural ventilation rate is overestimated

28. Results: Case 3 (continued) The maximum Helium concentration is located at the source and occupies much less space The column of the outflow gas is now much broader resulting in lower Helium concentrations inside the garage Flow pattern has reached steady state conditions at least at 3.600 seconds NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY

29. Conclusions The ADREA-HF CFD code was successfully applied to simulate 3 full scale Helium release experiments The predicted results were generally in acceptable agreement with the experimental data The calculations revealed the mixing patterns Mixing mechanisms reached a near-equilibrium state resulting in a constant cloud size and shape during the release period CFD practice is important for evaluation of potential hazards especially under complex release conditions NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY

30. Future Plans Evaluation of the performance of other turbulence models under the same experimental conditions Development of CFD practice guidelines for such kind of flows NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY

31. Acknowledgements NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY The authors would like to thank the Greek Secretariat of Research and Technology as well as the European Commission for funding for this work through the 02-PRAKSE-42 and HYSAFE-NoE projects respectively

32. NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Animation (Case 1)

33. NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Animation (Case 1 continued )

34. NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Animation (Case 2)

35. NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Animation (Case 2 continued )

36. NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Animation (Case 3)

37. NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Animation (Case 3 continued )

38. Methodology III. Initial & Boundary Conditions * 1 normal velocity obtained from continuity equation * 2 function of the flow direction Wall function for velocity: Wall function for k: Wall function for ε: NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Solid building surfaces (28) Solid domain surface (ground) SourceFree domain surfaces (5) West sideEast sideSouth sideSymmetry planeTop plane u Wall function *2*2 *2*2 v *2*2 *2*2 *2*2 w *2*2 *2*2 *2*2 *1*1 q *2*2 *2*2 *2*2 *2*2 P T k *2*2 *2*2 *2*2 *2*2 ε *2*2 *2*2 *2*2 *2*2

39. Details of Numerical Solution Required CPU time (in seconds) of three cases NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY Required time (in seconds) to reach maximum time step

40. Relative error (%) of Cases 1, 2 and 3 NCSR "DEMOKRITOS" INSTITUTE OF NUCLEAR TECHNOLOGY & RADIATION PROTECTION ENVIRONMENTAL RESEARCH LABORATORY