1 national centre for scientific research demokritos, greece
DESCRIPTION
An Inter-Comparison Exercise On the Capabilities of CFD Models to Predict the Short and Long Term Distribution and Mixing of Hydrogen in a Garage. [email protected]. 1 National Centre for Scientific Research Demokritos, Greece 2 Universidad Politécnica de Madrid, Spain - PowerPoint PPT PresentationTRANSCRIPT
An Inter-Comparison Exercise On the Capabilities of CFD Models to Predict the Short and Long Term Distribution and Mixing of Hydrogen in a Garage
A.G. Venetsanos1, E. Papanikolaou1, M. Delichatsios1,10, J. Garcia2, O.R. Hansen3, M. Heitsch4, A. Huser5, W. Jahn6, T. Jordan7, J-M. Lacome8, H.S. Ledin9, D. Makarov10, P. Middha3, E. Studer11, A.V. Tchouvelev12, A. Teodorczyk13, F. Verbecke10, M.M. Van der Voort14
1 National Centre for Scientific Research Demokritos, Greece
2 Universidad Politécnica de Madrid, Spain
3 GEXCON AS, Norway
4 Gesellschaft für Anlagen-und Reaktorsicherheit (GRS)mbH, Germany
5 Det Norske Veritas, Norway
6 Forschungszentrum Juelich, Germany
7 Forschungszentrum Karlsruhe, Germany
8 Institut National de l’Environnement industriel et des RISques, France
9 Health and Safety Laboratory, UK
10 University of Ulster, UK
11 Commissariat à l’Energie Atomique
12 A.V.Tchouvelev & Associates, Canada
13 Warsaw University of Technology, Poland
14 TNO, The Netherlands
Slide 2
Outline
Scope of work SBEP-V3 specifications SBEP-V3 participation SBEP-V3 results
Evaluation methodology Blind phase Post phase
Conclusions
Slide 3
SBEPV3 Scope of work
To investigate for small hydrogen releases (<1g/s) within confined spaces on the phenomena occurring during the: Release period (short term) Diffusion period, i.e. long after the end of the release (long term)
To test the predictive ability of models/codes/organizations related to the above phenomena by performing New experiments and in parallel Blind simulations of the new experimental set
To develop consensus for the reasons of discrepancies between: Different predictions using same models Predictions of given models and experiment data
To improve our predictive ability by performing non-blind post calculations of the new experimental data
Slide 4
SBEPV3 Specifications
Sensor X (cm) Y (cm) Z (cm)1 0 0 2834 40 0 2836 140 0 2837 1.84 0 2838 140 0 2689 140 0 23810 140 0 18811 140 0 13812 140 0 8813 0 0 26814 0 0 23816 0 0 138
Plastic sheet
Enclosure size: 7.2 x 3.78 x 2.88 m
H2 mass flow rate: 1 g/sNozzle diameter: 20 mmExit velocity: 38.4 m/sRelease duration: 240 sTest duration: 5400sAmbient temperature: 10 °CTarget concentration: 3.53%
Height 265mm
Diameter: 120mm
Release chamber
Slide 5
SBEPV3 Participants 12 HYSAFE partners:
CEA Commissariat à l’Energie Atomique, France DNV Det Norske Veritas, Norway FZJ Forschungszentrum Juelich, Germany FZK Forschungszentrum Karlsruhe, Germany GXC GEXCON AS, Norway HSL Health and Safety Laboratory, UK INERIS Institut National de l’Environement industriel et des
RISques, France NCSRD National Center for Scientific Research “Demokritos”,
Greece TNO Defence, Security and Safety Process Safety and
Dangerous Goods, The Netherlands UPM Universidad Politécnica de Madrid, Spain UU University of Ulster, UK WUT Warsaw University of Technology, Poland
2 non-HYSAFE partners: AVT A.V.Tchouvelev & Associates Inc., Canada GRS Gesellschaft für Anlagen-und Reaktorsicherheit, Germany
Slide 6
SBEPV3 CFD codes
10 CFD codes applied: ADREA-HF CAST3M CFX 5.7.1 CFX 10.0 FDS 4.0 FLACS 8.1 FLUENT 6.2 GASFLOW 2.4.12 KFX PHOENICS 3.6
Slide 7
SBEPV3 Turbulence models 8 turbulence models applied:
Simple models LVEL LVEL model ML Generalized mixing length
Two equations models: KE Standard k-ε RNG RNG k- ε REAL Realizable k- ε SST SST model
LES models Smagorinski subgrid RNG subgrid
Slide 8
CaseTurbulence
modelCFD Code
Blind calculations simulation time (s)
Post calculations simulation time (s)
Analytical - 240LVEL_AVT
LVELPHOENICS 3.6 5400A 0-240 s LVEL, 240-5400 s laminar
LVEL_NCSRD ADREA-HF 5400 5400ML_CEA Mixing length CAST3M 5400 800
KE_DNV_a
Standard k- with buoyancy effects
FLACS 8.1 800KE_DNV_b KFX 240 240
KE_FZJ CFX 10.0 5400A 5400KE_FZK GASFLOW 2.4.12 5400 5400KE_GRS CFX 10.0 337A
KE_GXC FLACS 8.1 5400
KE_NCSRD ADREA-HF 5400 5400KE_TNO FLUENT 6.2 - 240KE_UPM FLUENT 6.2 5400 0-240 k-, 240-2980 laminar
REAL_WUT Realizable k- FLUENT 785
RNG_AVT RNG k- PHOENICS 3.6 5400A 0-240 s RNG k-, 240-5400 s laminarSST_GRS
SSTCFX 10.0 0-438 s, 438-1043A 905
SST_HSL CFX 5.7.1 5400 5400 s, CFX 10.0LES_NCSRD LES Smagorinsky FDS 4.0 110 2000
VLES_UU LES- RNG FLUENT 6.2.16 5400 5000 s, LES Smagorinski
SBEPV3 Participation matrix
Slide 9
SBEPV3 Evaluation methodology
op
op
CC
CCMRB 2
2
4
op
op
CC
CCMRSE
Statistical measures:
Mean relative bias
Mean relative square error
.....Averaging over all SBEP participant predictions for given sensor
pC Predicted mean molar concentration (time averaged)
oC Observed mean molar concentration (time averaged)
Duijm et al. (1996) Journal of Loss Prevention in the Process Industry, Vol 9
Ideal values: 0MRB 0MRSE
Slide 10
SBEPV3 Blind Example prediction
Blind prediction (NCSRD)
Release phase: 0-240s Diffusion phase: 240-5400s
Slide 11
SBEPV3 Blind Release phase
0
0.5
1
1.5
2
2.5
3
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Sensor No
Cp
/Co
LVEL_AVT
LVEL_NCSRD
ML_CEA
KE_DNV_a
KE_DNV_b
KE_FZJ
KE_FZK
KE_GRS
KE_GXC
KE_NCSRD
KE_UPM
REAL_WUT
RNG_AVT
SST_GRS
SST_HSL
VLES_UU
LES_NCSRD
Time series averaging period 30-240 s
Large spread for sensors along the jet
Large spread for sensors close to the ground and at large lateral distances from jet
All sensors
Slide 12
SBEPV3 Release Phase
Sensor z/LMo Region CBouss(%) C (%) Co (%)
16 4.79 BJ 20.11 16.94 16.50
15 6.94 BP 12.00 10.80 -
14 9.09 BP 7.67 7.16 8.04
13 10.39 BP 6.15 5.82 6.52
Paranjpe (2004)Buoyant jets: 55.0 MoLz
Buoyant plumes: 5MoLz Chen and Rodi (1980)
Comparison of data with existing correlations for sensors along jet axis
Relatively good agreementBoussinesqu approximation overestimates concentrations
Slide 13
SBEPV3 Blind Release phase
Sensor 16
0
5
10
15
20
25
30
35
40
0 100 200 300 400 500Time (s)
H2
con
cen
trat
ion
(b
y vo
l. %
)
LVEL_AVT LVEL_NCSRD
ML_CEA KE_DNV_a
KE_DNV_b KE_FZJ
KE_FZK KE_GXC
KE_GRS KE_NCSRD
KE_UPM REAL_WUT
RNG_AVT SST_GRS
SST_HSL VLES_UU
LES_NCSRD EXP_INERIS
Sensor 16
Group of LVEL_NCSRD and LVEL_AVT
Mixing length too much mixingLES-RNG too much mixing
LES-Smagorinski (Cs=0.2) too low mixing
KE_FZJ strangely low
KE_DNV_b strangely high
Group of KE_UPM, KE_NCSRD, KE_GRSRNG_AVT and REAL_WUT
Group of KE_GXC, KE_DNVa, KE_FZKSST_GRS, SST_HSL and INERIS data
Slide 14
SBEPV3 Blind Diffusion phase
0
0.5
1
1.5
2
2.5
3
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Sensor No
Cp
/Co
LVEL_AVT
LVEL_NCSRD
ML_CEA
KE_DNV_a
KE_FZJ
KE_FZK
KE_GXC
KE_NCSRD
KE_UPM
REAL_WUT
RNG_AVT
SST_GRS
SST_HSL
VLES_UU
Time series averaging period 300-5400 s
All sensors
Mixing overestimated: Lower concentrations closer to the ceiling
Mixing overestimated: higher concentrations close to the ground
Slide 15
SBEPV3 Blind Diffusion phase
Sensor 12
0
1
2
3
4
5
6
0 1000 2000 3000 4000 5000Time (s)
H2
con
cen
trat
ion
(b
y vo
l. %
)
LVEL_AVT LVEL_NCSRDML_CEA KE_DNV_aKE_FZJ KE_FZKKE_GXC KE_NCSRDKE_UPM REAL_WUTRNG_AVT SST_GRSSST_HSL VLES_UUEXP_INERIS
Sensor 12
Group of KE_GXC, KE_DNV_a, KE_FZJ
Lower mixing is required
Slide 16
SBEPV3 Diffusion phase
Sensor Co (%)
1 7.37
4 7.36
6 7.39
7 7.21
8 7.19
9 6.84
10 5.57
11 2.87
12 0.89
13 7.29
14 6.84
16 2.75
Averaging time period 300-5400 s
Average flammable cloud boundary
Slide 17
0
10
20
30
40
50
0 1000 2000 3000 4000 5000Time (s)
Fla
mm
able
mix
ture
vo
lum
e (m
3)
LVEL_AVT LVEL_NCSRD ML_CEAKE_DNV_a KE_FZJ KE_FZKKE_GXC KE_NCSRD KE_UPMRNG_AVT SST_GRS SST_HSLVLES_UU
SBEPV3 Blind Diffusion phase
Risk assessment parameters
Too much mixing. Transition to homogeneous conditions. Group of LVEL_NCSRD, ML_CEA, KE_UPM, RNG_AVT, SST_GRS, VLES_UU
Stratification. Group of LVEL_AVT, KE_FZK, KE_NCSRD, KE_GXC, KE_DNV_a, KE_FZJ, SST_HSL
Slide 18
SBEPV3 Post Improvement steps Numerical options
Grid Improved vertical grid resolution
Some partners used the GEXCON grid Time step
Reduced for both release and diffusion phases Convective discretization scheme
Higher order schemes used Physical models
LES Smagorinski constant set to 0.1-0.12
Turbulence switched manually off short after release RNG_AVT and LVEL_AVT
Turbulent Schmidt number Consistent use of the 0.7 value
Slide 19
SBEPV3 Post Release phase
Sensor 16
0
5
10
15
20
25
30
35
40
0 100 200 300 400 500Time (s)
H2
con
cen
tra
tio
n (
by
vo
l. %
)LVEL_AVT LVEL_NCSRD
ML_CEA KE_DNV_a
KE_DNV_b KE_FZJ
KE_FZK KE_GRS
KE_GXC KE_NCSRD
KE_TNO KE_UPM
REAL_WUT RNG_AVT
SST_GRS SST_HSL
VLES_UU LES_NCSRD
EXP_INERIS
Sensor 16
Slide 20
SBEPV3 Post Diffusion phaseSensor 12
0
1
2
3
4
5
6
0 1000 2000 3000 4000 5000Time (s)
H2
con
cen
trat
ion
(b
y vo
l. %
)
LVEL_AVT LVEL_NCSRD
ML_CEA KE_DNV_a
KE_FZJ KE_FZK
KE_GXC KE_NCSRD
KE_UPM REAL_WUT
RNG_AVT SST_GRS
SST_HSL VLES_UU
LES_NCSRD EXP_INERIS
Slide 21
SBEPV3 Post Diffusion phase
0
10
20
30
40
50
0 1000 2000 3000 4000 5000Time (s)
Fla
mm
able
mix
ture
vo
lum
e (m
3)
LVEL_AVT LVEL_NCSRD
ML_CEA KE_DNV_a
KE_FZJ KE_FZK
KE_GXC KE_NCSRD
KE_UPM RNG_AVT
SST_GRS SST_HSL
VLES_UU
Slide 22
SBEPV3 Release phase
Sensor Co (%)Blind Post
MRB MRSE MRB MRSE
1 7.34 0.12 0.08 0.11 0.05
4 5.97 0.00 0.01 0.03 0.01
6 5.30 -0.06 0.02 0.00 0.02
7 4.69 0.05 0.02 0.11 0.03
8 4.70 -0.06 0.03 -0.01 0.02
9 3.78 0.00 0.02 0.08 0.02
10 3.07 -0.12 0.06 -0.06 0.02
11 0.66 0.55 0.73 0.44 0.38
12 0.06 0.93 2.04 0.36 1.69
13 6.52 0.27 0.14 0.25 0.10
14 8.04 0.16 0.12 0.15 0.07
16 16.50 0.06 0.16 0.13 0.09
Averaging time period 30-240 s
Slide 23
SBEPV3 Diffusion phase
Sensor Co (%)Blind Post
MRB MRSE MRB MRSE1 7.37 -0.33 0.14 -0.15 0.04
4 7.36 -0.33 0.14 -0.15 0.04
6 7.39 -0.33 0.14 -0.15 0.04
7 7.21 -0.30 0.13 -0.13 0.03
8 7.19 -0.31 0.13 -0.13 0.03
9 6.84 -0.29 0.12 -0.11 0.03
10 5.57 -0.19 0.06 -0.04 0.01
11 2.87 0.24 0.07 0.18 0.07
12 0.89 0.76 0.79 0.17 0.62
13 7.29 -0.32 0.14 -0.14 0.04
14 6.84 -0.29 0.12 -0.11 0.03
16 2.75 0.28 0.10 0.20 0.10
Averaging time period 300-5400 s
Slide 24
SBEPV3 Conclusions Release phase
The effect of the turbulence model is clearly important. In the jet region the standard k-ε model when applied without previous
knowledge of the experimental data (blind prediction) generally tended to overestimate the concentrations. This was shown to be rectified either:
using a low turbulent Schmidt number (0.3) in combination with a first order upwind scheme or
using the usual value of 0.7 for turbulent Schmidt combined with a smaller time step and higher order convective scheme.
From the two approaches the second is recommended. RNG k- ε and Realizable k- ε models showed tendency to overestimate
the concentrations. LVEL model generally tended to underestimate concentrations. The SST model was found to produce hydrogen concentrations in the
jet region lower than the standard k- model and in better agreement with the present experiment.
The LES Smagorinski model was found in good agreement with measured concentrations when the Smagorinski constant was set equal to 0.12
Slide 25
SBEPV3 Conclusions Diffusion phase
Experiments showed that a layer of hydrogen exists close to the ceiling, which is horizontally quasi homogeneous and vertically stratified.
Blind predictions showed two types of physical behaviour, either approximately constant stratification or fast transition to homogeneous hydrogen (non-flammable) distribution in the room.
Improvement of the predictions and reduction of spread between models was achieved in the post phase mainly by:
applying time step restrictions reduction of vertical grid spacing increase of the order of the convective scheme
The option of “manually” turning the turbulence model off although improved predictions in some cases cannot be suggested as a general recommendation.
Comparison between predicted and observed concentrations shows that the models generally tend to overestimate turbulent mixing
Work funded by EC