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Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
1
Modelling of H2 Dispersion and Combustion Phenomena Using CFD
CodesH. Paillère, E. Studer, A. Beccantini, S. Kudriakov,
F. Dabbene and C. Perret*CEA Saclay – *CEA Grenoble
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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Outline
• Introduction• Description of phenomena related to H2 risk issues• CFD modelling at CEA• Dispersion / Distribution model validation• Combustion model validation• Mitigation model validation• Outline of a validation matrix ?• Necessity for new experiments in support of code
validation• On-going activities and conclusions
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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Introduction (1/2)
• CEA has more than 10 years experience in the field of hydrogen safety, mainly in the field of nuclear safety (e.g. TMI accident in USA, 1979, 400kg H2 burn inside containment)
• Since 2001, CEA is actively engaged in the development of new energy technologies including hydrogen & fuel cell systems (over 250 engineers and technicians)
• Safety has been recognized as an important issue to ensure the success of these technologies
• CEA is a member of the HYSAFE Network of Excellence
H2+1/2O2
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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Introduction (2/2)• In many industrial fields, safety demonstrations
have relied mainly on expertise, supported by experiments.
• Increasingly, numerical tools, in particular, Computational Fluid Dynamics (CFD) codes, are being used for safety assessment, e.g. to predict explosive cloud formations or to assess consequences of explosions or flames
• Requirements on use of CFD results for safety assessment:– Code validation on representative experimental data (need to identify relevant phenomena & associated test data)– Expertise of code users– Application / knowledge of Best Practice Guidelines
• An international consensus on a CFD code validation matrix would be an additional factor to support CFD for H2 safety
CEA tests of H2 tank crash
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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Description of phenomena related to H2 risk issues• Review of accident scenarios and identification of main phenomena (on-
going PIRT exercise for example, within HYSAFE) List of phenomena (also identification of state of the art in modelling, existence of experimental data)
• Accidents involving H2 usually involve:– Release (gaseous or liquid)– Dispersion into environment, confined, semi-confined or open atmospheres– Action of passive or active mitigation systems to reduce the risk– In case of ignition, and depending on geometry & other parameters
• Diffusion flames• Jet fires• Slow deflagrations• Flame acceleration• DDT
• Very wide range of flow regimes involving chemical & heat transfer processes, from nearly incompressible buoyant flow to fully compressible reactive flow
• Challenge for physical models & numerical algorithms• Validation of models requires a very extensive effort
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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• Mainly relies on CAST3M code, which is an in-house research code, used for many different applications
• Not a “black box” code knowledge of models & methods… and their weaknesses
• Development of numerical algorithms “best suited” to the physics– Pressure based methods for dispersion calculations– Density based methods (shock capturing) for explosion modelling
• Trying to apply BPG (grid sensitivity, parametric studies, etc) … but very often beyond code & current computers’ capabilities
• Participation to benchmarks (e.g. HYSAFE)• Other codes are being/will be assessed & used by CEA
(e.g. FLUENT as well as two-phase flow codes)
CFD modelling at CEA
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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Dispersion / Distribution model validation
• Main physical models:– Laminar diffusion– Turbulence– Buoyancy forces
• Test cases: – Russian-2 experiment (HYSAFE benchmark)– AECL Large Scale Gas Mixing Facility Helium tests– CEA MISTRA Helium tests MH1 and MH2
• All confined atmosphere cases – in 3D geometries with no internal obstaclesBuoyant Gas Volume Fully confined Duration Physical phenomena
Russian-2 H2 20m3 Yes 250mn jet release during 1mn followed by diffusion phaseAECL LSGMF He 1000m3 No (p=Ct) 10mn jet release during 10mn
MISTRA He 100m3 Yes 120mn jet release during 30mn followed by diffusion phase
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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Russian-2 experiment (HYSAFE bench., see 120004)
• Experimental data not of very high quality (no repeatability, no information on wall temperatures)
• Grid and model (mixing length) sensitivity studies were performed
• Under-prediction of diffusion in the lower part of the facility (as with most codes)
• Effect of buoyancy forces due to temperature effects?
Grid convergence study
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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AECL LSGMF He tests
• Study of dynamics of buoyant jet
• Side opening in facility so constant pressure was maintained
• Comparison of different turbulent models was made, RNG k- vs. standard k
• Better accuracy was found using RNG k-
• Similar conclusion found using CFX (GRS)
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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MISTRA He tests MH1 and MH2• Release of He in purely confined geometry
(small pressurisation) to study physics of stratification, and mixing by diffusion
• Very well instrumented facility (gas sampling, thermocouples, LDV) detailed field measurements, including temperatures which might play a role in additional buoyancy effects
• Good agreement between CFD calculations & experimental data (velocity & concentration profiles)
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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Combustion model validation• Focus on confined/semi-confined H2, large scale experiments,
many of which performed in framework of nuclear safety studies:– HDR E12.3.2 Test, slow deflagration– Battelle BMC Ex29 Test, slow deflagration– RUT STH 06, fast deflagration– RUT STM4 Test, detonation
• Model implemented in CAST3M code: Compressible Euler equations with CREBCOM model. Diffusion and turbulence effects taken into account through experimental-based correlations (flame speed) – predictability of such model?
• Validation efforts aimed at showing ability to calculate dynamic loads (conservative values) rather than detailed physics
Volume (order magnitude) [H2] Physical phenomena
HDR E12.3.2 500m3 12% Slow deflagration, with acceleration through ventBMC Ex29 100m3 10% Slow deflagration, with acceleration through ventRUT STH06 500m3 16.5% Fast deflagrations with shock wavesRUT STM4 500m3 24.8% Detonation
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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HDR E12.3.2 test: slow deflagration• Slow deflagration through interconnected
volumes• Ability to model flame acceleration and
pressure effects by choosing appropriately model constants
• Grid sensitivity results show limitations of such simplified combustion model
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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BMC Ex29 test: slow deflagration• Slow deflagration through interconnected
volumes (similar to HDR test)• Ability to model flame acceleration and
pressure effects by choosing appropriately model constants
• Grid sensitivity results show limitations of such simplified combustion model
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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RUT STH06 test: fast deflagration• Flame acceleration modelled using CREBCOM model• Presence of shock waves (precursor and reflected shock waves)• Good agreement with experimental data
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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RUT STM4 Test: detonation• Flame acceleration & transition not modelled• Simulate detonation entering canyon & reflection• Results not dependent on CREBCOM model parameters.
Code gives similar results with global Arrhenius model• Ability to capture pressure peaks if grid sufficiently fine &
second-order schemes used
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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Mitigation model validation• Mitigation effects can also be evaluated using CFD• For example: use of catalytic recombiners as a risk-reducing
measure in confined environments or to decrease H2 content of release (for ex. Boil-off system for LH2 engines)
• CEA has performed experiments to qualify recombiner systems & developed model incorporated in CAST3M code
• Model development for other types of mitigation devices & appropriate experimental validation to be carried out in HYSAFE
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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Outline of a validation matrix?Name of experiment
Media Geometry, Scale
Open, semi-confined or confined atmosphere
Main phenomena Quality of experimental data (High – Medium - Low)
Features of validation
RUSSIAN-2 GH2 Cylindrical vessel, 5.5m high, 2.2m diameter, 20m3 vol.
confined Subsonic release near the top at a rate of 4.5l/s for 60s, then diffusion over a period of 250min
Low grid-dependence
AECL LSGMF
GHe Rectangular room, 1000m3
Confined Buoyant jet release of 3g/s at a speed of 8.6m/s for 600s
High turbulence model
MISTRA MH1-MH2
GHe Cylindrical vessel, 7m high, 4m diameter, 100m3
Confined Buoyant jet release of 1 g/s for 1800s, then diffusion over a period of 7000s
High Preliminary calculations
NASA-6 LH2 40m Open, non congested
spill of LH2, evaporation, heat transfer ground, atmospheric dispersion, buoyancy forces
Medium On-going (coupling FLUENT- CAST3M codes)
Fh-ICT Balloon
GH2 80m Open, non congested
Deflagration of a 20m diameter half-sphere and propagation of pressure waves over a distance of 80m
Medium model parameters, grid dependence
HDR E12.3.2
GH2 + steam
Series of interconnected rooms of respective volumes 140m3, 75m3 and 330m3
Semi-confined (last room vented)
Ignition at far end of a hydrogen, steam and air mixture followed by flame propagation (deflagration) and acceleration
Low (designed for lumped-parameter codes)
model parameters, grid dependence
BATTELLE BMC Ex29
GH2 Series of two interconnected rooms of 41m3 vol. each
Semi-confined (second room vented)
Ignition at far end followed by flame propagation (deflagration) and acceleration
Low (same reason as above)
model parameters, grid dependence
RUT STH06 GH2 Two long channels (about 36m each) separated by large vol. (canyon), overall volume 480m3
Confined
Fast deflagration High grid dependence
RUT STM4 GH2 + steam
Same as above
Confined Fully developed detonation entering the canyon
High grid dependence, order schemes
KALI GH2 + steam
Steel vessel of 15.6m3
Confined Global H2 reduction through the use of a Passive Autocatalytic Recombiner
Low None
• Current identified gaps:– Separate Effect
Tests (eg. Pure diffusion)
– Low momentum release in confined atmospheres
– Release in obstacle-laden environments
– Release in partially / open atmospheres
– Combustion in presence of gradients
– Diffusion flames & jet fires
• Need for new experiments
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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New tests at CEA: Diffusion column experiment• Some doubts as to the mixing
processes in Russian-2 test:– Other than molecular diffusion?
• GADIFAN Separate Effect Test • Study of diffusion mixing. No
injection, light gas separated from air by diaphragm that can be opened without disturbing the flow
• He or H2 can be compared• Column can be tilted at various
angles (to introduce buoyancy)
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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New tests at CEA: detailed mixing experiment• GAMELAN test for study of He
injection & mixing• Use of non-intrusive
measurement techniques (LIF) for gas concentration measurements
• Also LDV measurements of velocity
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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New tests at CEA: compartmented tests• Objective: study mixing
processes in a confined, compartmented geometry (public multi-storey car park)
• Additional physical processes:– Jet impinging– Additional turbulence
created by flow around obstacles
• Use of large scale (7m high, 100m3) facility MISTRA facility (developed for other applications)
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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New tests at CEA & INERIS: garage experiments• Garage tests “à la Swain”, performed in the framework
of HYSAFE’s insHYde project, for typical European garage layouts
• Detailed measurements for CFD code validation (various concentration measurement techniques will be tested)
• He release (CEA) & H2 release (INERIS) experiments• Study of geometric configurations, effect of ventilation
H2
H2
Heor
Several vent locationswith possibility of mechanical ventilation
Simulated car
vent
ventVarying roof inclination
X
Hydrogen or Helium : various locations for injection
Large experimental hall forwell controled external boundary
conditions (stable temperature, no wind)
Paper 100071 – Paillère et al.International Conference on Hydrogen Safety,ICHS, Pisa, September 8-10, 2005
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On-going activities and conclusions• Presentation of validation efforts performed at CEA for H2 risk
assessment• More work on model development & validation needed• Gaps in experimental data identified:
– Availability of existing (published) data– need for better experiments (quality of experimental data) – Need for new types of tests, including “Separate Effect Tests” &
“Coupled Effect Tests”• On-going experimental programme at CEA in support of code
modelling & validation• Main objective: stimulate discussions on an “internationally”-
agreed validation matrix for CFD codes to be used for H2 safety assessment– Within HYSAFE Network of Excellence– Among OECD / IEA Task 19 (H2 Safety) group of experts