Validation studies of CFD codes on hydrogen combustion

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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 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 During a postulated severe accident large amount of H 2 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 H 2 combustion in nuclear plant containment is an important exercise in this context. Motivation - ERMSAR 2012, Cologne March 21 23, AREVA NP GmbH Proprietary - AREVA - p.4

5 Three CFD codes used in this study: ANSYS CFX ANSYS FLUENT COM3D (Karlsruhe Institute of Technology) Objective 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 Solver Pressure-velocity, Pressure-based, coupled segregated Coupled, compressible Turbulence Model Shear Stress Transport RNG k-epsilon Standard k-epsilon Combustion Model Partially premixed: Partially premixed model BVM+EDM with PDF tables KYLCOM Laminar flame speed Liu and MacFarlane Liu and MacFarlane Exp. Database Turbulent flame speed Zimont, Dinkelacker Zimont Schmidt Slip conditions at walls No-slip No-slip Slip Thermal conditions at walls Heat flux with radiation Heat flux with radiation Adiabatic Grid Unstructured Unstructured Cubic structured Time Step Adaptive Fixed Adaptive - 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 m 3 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 Tetra, Prism layer Tetra, Prism layer Hexa,Tetra, Prism layer Ave. cell size m m m m Number of cells 81, ,435 3,223, ,323 Grid-independent solution Standard Tet-mesh is chosen - ERMSAR 2012, Cologne March 21 23, AREVA NP GmbH Proprietary - AREVA - p.9

10 S c S u t c~ Parameters in the Burning Velocity Model (BVM) Laminar burning velocity S l Liu and MacFarlane correlation Coupled BVM-EDM model in CFX: Parameter dependence 4.4 CO step( ) 1 min 2 CH 2 R Reaction Progress A, k k BVM reaction progress Sl Classic EDM reaction rate Model by Szabo (KIT): a function of temperature, pressure, mixture composition Turbulence burning velocity S t Zimont Model A=0.6 (default), A=1.7 Dinkelacker S S t t AGu' S l 3/ 4 S 1/ 2 l Re Le 1/ 4 1/ 4 u lt u S 0.25 ' t l 0.3 P P Said-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 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, AREVA NP GmbH Proprietary - AREVA - p.10

11 THAI experiments: Parameter sensitivity study Liu and S t S l MacFarlane KIT Zimont A=1.7 OK OK Zimont A=0.6 - Too slow! Dinkelacker OK Too slow! 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 bar bar bar Temperature C C C H 2 concentration 10 vol% 10 vol% 6-12 vol% H 2 O concentration 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, AREVA NP GmbH Proprietary - AREVA - p.12

13 THAI experiments: Comparison of CFX, FLUENT and COM3D HD-7 HD-8 HD-27 Pressure bar bar bar Temperature C C C H 2 concentration 10 vol% 10 vol% 6-12 vol% H 2 O concentration 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 bar bar bar Temperature C C C H 2 concentration 10 vol% 10 vol% 6-12 vol% H 2 O concentration vol% Burning direction upwards downwards upwards 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 3.3 m i.d m 1.7 m i.d 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 H 2 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 Hexa Hexa Ave. cell size [mm] dome [mm] acc.tube [mm] Number of cells 568,583 2,109, ,616 COM3D Obstacles BR=0.57 BR=0.63 coarse fine - 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