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Validation studies of CFD codeson hydrogen combustion
Sudarat Worapittayaporn, Luciana Rudolph, Harald DimmelmeierAREVA NP GmbH
ERMSAR 2012, Cologne, March 21 – 23, 2012
- ERMSAR 2012, Cologne March 21 – 23, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.3 All rights are reserved, see liability notice.
Content
Introduction
Validation resultsSlow combustion experiments in THAI facility
Fast combustion experiments in ENACCEF facility
Conclusions
- ERMSAR 2012, Cologne March 21 – 23, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.4 All rights are reserved, see liability notice.
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, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.5 All rights are reserved, see liability notice.
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, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.6 All rights are reserved, see liability notice.
Main differences of codes and models
CFX FLUENT COM3DVersion 12.1 13 4.0
SolverPressure-velocity,
coupledPressure-based,
segregatedCoupled, compressible
Turbulence Model Shear Stress Transport RNG k-epsilon Standard k-epsilon
Combustion ModelPartially premixed:
BVM+EDMPartially premixed model
with PDF tablesKYLCOM
Laminar flame speed Liu and MacFarlane Liu and MacFarlane Exp. DatabaseTurbulent flame speed Zimont, Dinkelacker Zimont SchmidtSlip conditions at walls No-slip No-slip SlipThermal conditions at
wallsHeat flux with radiation Heat flux with radiation Adiabatic
Grid Unstructured Unstructured Cubic structuredTime Step Adaptive Fixed Adaptive
Validation THAI Facility
Experiments
Modeling
Results
- ERMSAR 2012, Cologne March 21 – 23, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.8 All rights are reserved, see liability notice.
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
THAI facility: Description
Pressure monitoring
- ERMSAR 2012, Cologne March 21 – 23, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.9 All rights are reserved, see liability notice.
THAI experiments: Mesh sensitivity
Coarse Standard Fine HybridType of grid Tetra,
Prism layerTetra,
Prism layerTetra,
Prism layerHexa,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, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.10 All rights are reserved, see liability notice.
2,
1min
2.31
4.41)00002.0step( 22 HO
l
CC
kA
Sk
ProgressReactionR
Coupled BVM-EDM model in CFX:Parameter dependence
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
BVM reaction progressClassic EDM reaction rateSaid-Borghi
Factor
Parameters in the Eddy Dissipation Model (EDM)
Empirical coefficient A in the reaction rate: A = 8, A = 16
Modification with Said-Borghi factor
Zimont Model A=0.6 (default), A=1.7
Dinkelacker
|~| cSS tuc
4/14/12/14/3' tult lSuGAS
2.0
0
3.0
25.0 'Re
46.01
P
P
S
u
LeSS
ltlt
Sensitive to laminar and turbulent burning velocities
Not much influenced by EDM-A
Improvement by using Said-Borghi factor (very minor in slow combustion)
- ERMSAR 2012, Cologne March 21 – 23, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.11 All rights are reserved, see liability notice.
THAI experiments:Parameter sensitivity study
St SlLiu and
MacFarlaneKIT
Zimont A=1.7 OK OKZimont A=0.6 - Too slow!Dinkelacker OK Too slow!
HD-8: better predicted by Dinkelacker correlation
- ERMSAR 2012, Cologne March 21 – 23, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.12 All rights are reserved, see liability notice.
THAI experiments: Comparison of CFX, FLUENT and COM3D
HD-7 HD-8 HD-27Pressure 1.480 bar 1.487 bar 1.497 bar
Temperature 30-90°C 30-90°C 30-90°CH2 concentration 10 vol% 10 vol% 6-12 vol%
H2O concentration - - 3-47 vol%Burning direction upwards downwards upwards
Slower pressure development predicted
Combustion calculations sensitive to initial turbulence level (unknown in experiments)
- ERMSAR 2012, Cologne March 21 – 23, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.13 All rights are reserved, see liability notice.
THAI experiments: Comparison of CFX, FLUENT and COM3D
HD-7 HD-8 HD-27Pressure 1.480 bar 1.487 bar 1.497 bar
Temperature 30-90°C 30-90°C 30-90°CH2 concentration 10 vol% 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, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.14 All rights are reserved, see liability notice.
THAI experiments: Comparison of CFX, FLUENT and COM3D
HD-7 HD-8 HD-27Pressure 1.480 bar 1.487 bar 1.497 bar
Temperature 30-90°C 30-90°C 30-90°CH2 concentration 10 vol% 10 vol% 6-12 vol%
H2O concentration - - 3-47 vol%Burning direction upwards downwards upwards
Well predicted by all codes
Maximum pressure overestimated due to assumption of combustion completeness
Validation ENACCEF Facility
Experiment
Modeling
Results
- ERMSAR 2012, Cologne March 21 – 23, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.16 All rights are reserved, see liability notice.
1.7
mi.
d.
0.7
4 m
3.3
mi.
d.
0.1
54
m
ENACCEF facility: Description
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
9x obstacles
Ignition point
Pressure monitoring
- ERMSAR 2012, Cologne March 21 – 23, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.17 All rights are reserved, see liability notice.
ENACCEF – ISP 49 test run 765: Geometrical model
CFX&FLUENT Hex-coarse Hex-fine COM3D
Type of cell Hexa Hexa HexaAve. cell size [mm] 13.22 8.60 15.4 - dome [mm] 21.97 14.30 15.4 - acc.tube [mm] 8.55 5.58 15.4Number of cells 568,583 2,109,126 950,616
COM3D
ObstaclesBR=0.57 BR=0.63
coarse fine
- ERMSAR 2012, Cologne March 21 – 23, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.18 All rights are reserved, see liability notice.
ENACCEF – ISP 49 test run 765: Mesh and timestep sensitivity
Grid-independent solution in CFX achieved
CFX FLUENT
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
Time step too large
- ERMSAR 2012, Cologne March 21 – 23, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.19 All rights are reserved, see liability notice.
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, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.20 All rights are reserved, see liability notice.
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, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.21 All rights are reserved, see liability notice.
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, 2012 - AREVA NP GmbH Proprietary - © AREVA - p.22 All rights are reserved, see liability notice.
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.
End of presentationValidation study of CFD codeson hydrogen combustion
AREVA NP GmbH