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![Page 1: On numerical simulation of liquefied and gaseous hydrogen releases at large scales V. Molkov, D. Makarov, E. Prost 8-10 September 2005, Pisa, Italy First.](https://reader035.fdocuments.net/reader035/viewer/2022062714/56649d6b5503460f94a4ad5f/html5/thumbnails/1.jpg)
On On numerical simulation of numerical simulation of liquefied and gaseous liquefied and gaseous
hydrogen releases at large scaleshydrogen releases at large scales
V. Molkov, D. Makarov, V. Molkov, D. Makarov, EE. . ProstProst
8-10 September 2005, Pisa, Italy8-10 September 2005, Pisa, Italy
First International Conference onFirst International Conference on
HYDROGEN SAFETYHYDROGEN SAFETY
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• Introduction of hydrogen as an energy carrier makes great demands on hydrogen safety. Development of robust and reliable risk assessment methodologies requires all-round validation of models and tools.
• The need to model non-uniform hydrogen-air mixture formation at real scales is important to have realistic initial conditions for subsequent modelling of partially premixed hydrogen combustion.
• The aim of this study is validations of the LES model in application to large-scale hydrogen release scenarios and formulation of tasks for future research in this area.
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ContentsContents•The LES modelThe LES model
•LH2 release in open LH2 release in open
atmosphereatmosphere
•GH2 release in a closed vesselGH2 release in a closed vessel
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Large Eddy Simulation (LES) Large Eddy Simulation (LES) modelmodel
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• Conservation of massConservation of mass
•
• Conservation of momentumConservation of momentum
• Conservation of energyConservation of energy
LES model (1/LES model (1/22))
0~
jj
uρxt
ρ
iijk
k
i
j
j
ieff
jii j
j
i gρδx
u
x
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xx
p uuρ
xt
uρ
~
3
2~~~~
~
pEux
Et j
j
~~~
ijk
k
i
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m j
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peff
j x
u
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uu
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Y
Sch
x
Tc
x
~
3
2~~~
~~
~
Pr
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• RNG SGS turbulence modelRNG SGS turbulence model
• Conservation of “Conservation of “HH22”” concentrationconcentration
LES model (2/LES model (2/22))
31
3
2
1001
effs
eff H
ijijCVs S~
S~
V. 21570231
effeffeffeff
effeff ScNN
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3929.113679.06321.0
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jHj
jH x
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ScxYu
xY
t2
22
~~~
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Liquefied hydrogen release in Liquefied hydrogen release in open atmosphereopen atmosphere
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Chirivella J.E., Witcofski, R.D. Am. Inst. Chem.
Eng. Symp., 82, No 251, 1986, pp.120-142:
- Spill 5.11 m3 (361.8 kg) of LH2 in 38 s
- LH2 pool radius between 2 and 3 m
- Total evaporation time 43 s
- Wind speed ~2.2 m/s at height 10 m
NASA experimentNASA experiment
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Calculation domain (1/2)
180 m
70 m
Spill area and instrumentation towers area
Cloud propagation area
Characteristic size of CV: Numerical grid: 156133 CV– tower location 1.0 - 2.0 m– cloud area 2.0 - 3.0 m – the rest of domain up to 10 m
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Calculation domain (2/2)
70 m
180 m
Spill areaCloud propagation area
Characteristic size of CV: Numerical grid: 103163 CV– spill area 0.6 - 1.0 m– cloud area 2.0 - 3.0 m – the rest of domain up to 10 m
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Initial conditionsatmosphere velocity profile:where (provided u=2.2 m at H=10 m)
Boundary conditionsvelocity profile at inflow
prescribed pressure conditions at outflow boundaries, p=0 Pa
H2 injectionmass injection rate
Run 1: injection area radius
Run 2: injection area radius
average injection velocity
instant injection velocity
Run 1: turbulence
Run 2: turbulence
Geomerty: Run 1 (no pool border, no obstacles), Run 2 (+)
0* ln yykuzu ,40.0k ,03.00 my 2
* 1015.15 u
0* ln yykuzu
skgConstm 41.8
115.0 tR mR 5.2sts 100 st 10
poolaver AmV )2sin())(2sin(1( inf zntvxnIVV averinj 5.0n
99.0I
Numerical details
mR 5.2
99.0I sts 100 10.0I st 10
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H2 concentration (Run 1)
4%
52%
52% 4%
Texp = 21.33 sTsim = 21.36 s
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H2 concentration (Run 2)
4%52%
Texp = 21.33 sTsim = 21.35 s
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Simulated temperature (Run 1)
)
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Simulated temperature (Run 2)
)
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Visible cloud (Run 1)
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Visible cloud (Run 2)
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Cloud propagation (Run 1)
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Cloud propagation (Run 2)
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Phenomena to be addressed
• Condensation of air in temperature range Condensation of air in temperature range 20-90 K (with heat release) and evaporation 20-90 K (with heat release) and evaporation above 90 Kabove 90 K
• Two phase flow Two phase flow (gas: hydrogen-air; solid: air ice)(gas: hydrogen-air; solid: air ice)
• Detailed spill modelling (initial fractions of Detailed spill modelling (initial fractions of GH2 and LH2; heat transfer to the ground: GH2 and LH2; heat transfer to the ground: initial violent evaporation stage, etc)initial violent evaporation stage, etc)
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Gaseous hydrogen release in Gaseous hydrogen release in 20-m20-m33 closed vessel closed vessel
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5.5
m2.2m
ExperimentExperiment
1.4m
H2
Time of release = 60 seconds
Volume injection rate: V=4.5 l/s
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Non-uniform tetrahedral grid
CV number: 54004CV size: 0.01-0.10 m close to place of H2 injection CV size: up to 0.20 m in the rest of domain
“Uniform” grid
CV number: 28440CV size: 0.14-0.20 m
0-180 s0-180 s 3-251 min3-251 min
Calculation domainCalculation domain
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• Initial conditions– quiescent air, u=0 m/s,– initial air concentration Yair=1.0,– initial temperature T=293K
• Boundary conditions– t=0-1s: Vinj increased from 0 to 57.5 m/s– t =1-59s: Vinj=57.5 m/s– t=59-60s: decrease from 57.5 to 0 m/s– t=60s-251min: Vinj=0 m/s– YH2=1.0, Tinj=293K
• Numerical details– explicit linearisation of the governing equations– implicit method for solution of linear equation set– second order accurate upwind scheme for convection terms, central-
difference scheme for diffusion terms– Time steps: t=0-180 s: t=0.01 s; t=3-251 min: t=0.01-1.0 s
Numerical details
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Simulation results
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2 min2 min
50 min50 min 100 min100 min 250 min250 min
Hydrogen distribution 1
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Hydrogen distribution 2
Vessel depth, m
H2
vol.
con
cen
trat
ion
0 1 2 3 4 5 60
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
Experiment: 2 minExperiment: 50 minExperiment: 100 minExperiment: 250 minSet 2 simulations: 2 minSet 2 simulations: 50 minSet 2 simulations: 100 minSet 2 simulations: 250 min
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50min:50min:VVmaxmax=10 cm/s=10 cm/s
100min:100min:VVmaxmax=8 cm/s=8 cm/s
250min:250min:VVmaxmax=5 cm/s=5 cm/s
Residual velocities
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Conclusions
• The LES model has been applied to analyse large-scale experimental LH2 and GH2 releases.
• The simulation of non-uniform flammable cloud formation, resulting from a LH2 spill, reproduced a characteristic structure of the turbulent eddies and the direction of cloud propagation.
• The simulation results were found to depend on initial and boundary conditions.
• The air condensation-evaporation sub-model may improve predictive capabilities of the LES model
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Conclusions
• Good agreement was achieved with experimental data on GH2 release in 20-m3 closed vessel up to t=250 min after the 1 minute release.
• The LES results demonstrated that random flow field remains in the vessel long time after the injection and this is presumably responsible for H2 transport.
• Further experiments with observation of velocity field after release and simulations with higher accuracy are required to give final answer to this question.