2. Validation studies of CFD codes on hydrogen combustion
Sudarat Worapittayaporn, Luciana Rudolph, Harald Dimmelmeier
AREVA NP GmbH
ERMSAR 2012, Cologne, March 21 – 23, 2012

3. Content Introduction Validation results Conclusions
Slow combustion experiments in THAI facility
Fast combustion experiments in ENACCEF facility
Conclusions
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.3

4. Motivation
During a postulated severe accident large amount of H2 can accumulate in the containment, which exhibits a potential risk to the structure integrity.
CFD tools have been applied in containment analysis to:
Calculate the gas mixture distribution in containment
Calculate combustion of a predefined gas mixture
Yield dynamic pressure loads on internal walls and containment shell
Assess risk of deflagration-to-detonation transition
Evaluation of the applicability of CFD codes to predict the H2 combustion in nuclear plant containment is an important exercise in this context.
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.4

5. Objective Three CFD codes used in this study:
ANSYS CFX
ANSYS FLUENT
COM3D (Karlsruhe Institute of Technology)
Selection of most-appropriate models, parameter sensitivity, and calibration of models and correlations are part of this study.
Validation against data of selected experiments with specified conditions relevant to containment analysis, e.g.:
Slow and fast combustion
Negative hydrogen concentration gradient
Upwards and downwards burning direction
Steam and hydrogen concentration gradient
Confined geometry with obstacles
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.5

6. Main differences of codes and models
CFX
FLUENT
COM3D
Version
12.1 13
4.0
Solver
Pressure-velocity, coupled
Pressure-based, segregated
Coupled, compressible
Turbulence Model
Shear Stress Transport
RNG k-epsilon
Standard k-epsilon
Combustion Model
Partially premixed: BVM+EDM
Partially premixed model with PDF tables
KYLCOM
Laminar flame speed
Liu and MacFarlane
Exp. Database
Turbulent flame speed
Zimont, Dinkelacker
Zimont
Schmidt
Slip conditions at walls
No-slip
Slip
Thermal conditions at walls
Heat flux with radiation
Adiabatic
Grid
Unstructured
Cubic structured
Time Step
Adaptive
Fixed
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.6

7. Validation THAI Facility
Experiments
Modeling
Results

8. THAI facility: Description
Large scale test facility operated by Becker Technologies GmbH
Cylindrical stainless steel vessel of 9.2 m height and 3.2 m diameter with a total volume of 60 m3
Inner cylinder and condensate trays are removed for the hydrogen deflagration (HD) tests
Tests with up- and downwards flame
Fully instrumented
Pressure monitoring
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.8

9. THAI experiments: Mesh sensitivity
Coarse
Standard
Fine
Hybrid
Type of grid
Tetra, Prism layer
Hexa,Tetra, Prism layer
Ave. cell size
0.331 m
0.199 m
0.135 m
0.204 m
Number of cells
81,626
452,435
3,223,535
181,323
Grid-independent solution
Standard Tet-mesh is chosen
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.9

10. Coupled BVM-EDM model in CFX: Parameter dependence
BVM reaction progress
Classic EDM reaction rate
Said-Borghi Factor
Parameters in the Burning Velocity Model (BVM)
Laminar burning velocity Sl
Liu and MacFarlane correlation
Model by Szabo (KIT): a function of temperature, pressure, mixture composition
Turbulence burning velocity St
Parameters in the Eddy Dissipation Model (EDM)
Empirical coefficient A in the reaction rate: A = 8, A = 16
Modification with Said-Borghi factor
Sensitive to laminar and turbulent burning velocities
Zimont Model A=0.6 (default), A=1.7
Dinkelacker
Not much influenced by EDM-A
Improvement by using Said-Borghi factor (very minor in slow combustion)
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.10

11. THAI experiments: Parameter sensitivity study
St Sl
Liu and MacFarlane
KIT
Zimont A=1.7 OK
Zimont A=0.6 -
Too slow!
Dinkelacker
HD-8: better predicted by Dinkelacker correlation
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.11

12. THAI experiments: Comparison of CFX, FLUENT and COM3D
HD-7
HD-8
HD-27
Pressure
1.480 bar
1.487 bar
1.497 bar
Temperature
30-90°C
H2 concentration
10 vol%
6-12 vol%
H2O concentration -
3-47 vol%
Burning direction
upwards
downwards
Slower pressure development predicted
Combustion calculations sensitive to initial turbulence level (unknown in experiments)
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.12

13. THAI experiments: Comparison of CFX, FLUENT and COM3D
HD-7
HD-8
HD-27
Pressure
1.480 bar
1.487 bar
1.497 bar
Temperature
30-90°C
H2 concentration
10 vol%
6-12 vol%
H2O concentration -
3-47 vol%
Burning direction
Upwards
downwards
upwards
Combustion progress involves two regimes (slow and fast)
None of the codes can completely reproduce entire combustion progress (slow and fast)
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.13

14. THAI experiments: Comparison of CFX, FLUENT and COM3D
HD-7
HD-8
HD-27
Pressure
1.480 bar
1.487 bar
1.497 bar
Temperature
30-90°C
H2 concentration
10 vol%
6-12 vol%
H2O concentration -
3-47 vol%
Burning direction
upwards
downwards
Well predicted by all codes
Maximum pressure overestimated due to assumption of combustion completeness
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.14

15. Validation ENACCEF Facility
Experiment
Modeling
Results

16. ENACCEF facility: Description
1.7 m i.d m
3.3 m i.d m
Located in France and operated by CNRS
Consists of two parts:
Acceleration tube and dome
Acceleration tube with 9 annular obstacles
Blockage ratio of 0.63
Flame develops in the upwards direction
Initial negative H2 concentration gradient:
from 11.6% vol. in the lower part of the facility to 8.0% vol. in the upper part
Instrumented to measure flame position, pressure build-up and gas composition
Pressure monitoring
9x obstacles
Ignition point
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.16

17. ENACCEF – ISP 49 test run 765: Geometrical model
CFX&FLUENT
Hex-coarse
Hex-fine
COM3D
Type of cell
Hexa
Ave. cell size [mm]
13.22
8.60
15.4
- dome [mm]
21.97
14.30
- acc.tube [mm]
8.55
5.58
Number of cells
568,583
2,109,126
950,616
COM3D
Obstacles BR=0.57
coarse
fine
BR=0.63
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.17

18. ENACCEF – ISP 49 test run 765: Mesh and timestep sensitivity
CFX
FLUENT
Time step too large
Grid-independent solution in CFX achieved
Influence of time step in FLUENT noticeable:
Coarse grid + large time step = insufficient
Coarse grid + small time step = sufficient
Fine grid + small time step = acceptable
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.18

19. ENACCEF – ISP 49 test run 765: Comparison of CFX, FLUENT and COM3D
Pressure evolutions: good agreement by all codes
Delay in pressure rise
Partially flame quenching? Or only transition of combustion regimes?
All codes failed to predict this behavior  Further model development and validation needed!
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.19

20. ENACCEF – ISP 49 test run 765: Comparison of CFX, FLUENT and COM3D
Slow flame propagation after the last obstacle (?)
Flame position and velocity: good agreement by CFX and FLUENT, underestimated by COM3D (BR=0.57 instead of 0.63, too coarse mesh)
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.20

21. Conclusions
Simulations results and their direct comparison to measured data show importance of using appropriate correlations for laminar and turbulent burning velocity.
All codes capture main process features with reasonable adequacy (predictions of global parameters, e.g. maximum pressure in slow and fast turbulent combustion regimes, are consistent and in fair agreement with experimental data)
Combustion models are very sensitive to initial turbulence
Apparently, some phenomena (like flame quenching, transition in combustion regime from fast to slow deflagration) are still a challenging situation for codes
Calculation results demonstrate that hydrogen safety analysis in containments using commercial CFD codes such as CFX or FLUENT is possible in near future
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.21

22. Any reproduction, alteration or transmission of this document or its content to any third party or its publication, in whole or in part, are specifically prohibited, unless AREVA has provided its prior written consent.
This document and any information it contains shall not be used for any other purpose than the one for which they were provided. 
Legal action may be taken against any infringer and/or any person breaching the aforementioned obligations.
- ERMSAR 2012, Cologne March 21 – 23, AREVA NP GmbH Proprietary - © AREVA - p.22

23. End of presentation Validation study of CFD codes on hydrogen combustion
AREVA NP GmbH