1 national centre for scientific research demokritos, greece

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

[email protected]

Outline

Scope of work SBEP-V3 specifications SBEP-V3 participation SBEP-V3 results

Evaluation methodology Blind phase Post phase

Conclusions

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

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

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

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

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

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

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

SBEPV3 Blind Example prediction

Blind prediction (NCSRD)

Release phase: 0-240s Diffusion phase: 240-5400s

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

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

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

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


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

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

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


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

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

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

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

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

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


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


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

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

1 national centre for scientific research demokritos, greece

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