During a severe accident in a nuclear power plant, hydrogen would be generated due to the oxidation of metallic components in steam atmosphere. In the containment hydrogen would form a combustible mixture, posing a deflagration or even detonation risk threatening the integrity of the containment. In order to estimate possible loads generated by the hydrogen combustion, reliable numerical tools are needed to simulate the deflagration process. Recently, the French MITHYGENE project consortium and the European Technical Safety Organisation Network (ETSON) organized a benchmark on hydrogen combustion to identify the current level of the computational tools in the area of hydrogen combustion simulation under a severe accident typical conditions. The benchmark was based on the experiments performed in the ENACCEF2 facility. The benchmark conclusions indicated that there are still limitations and weaknesses present in the combustion models used in the different codes. These limitations concern the chemistry part, turbulent combustion model and the coupling between the two models.

This paper presents post-benchmark simulations of ENACCEF2 facility premixed hydrogen combustion experiments. The presented simulations were performed using a custom-built turbulent combustion OpenFOAM solver based on the progress variable model.

The ENACCEF2 facility is a vertical acceleration tube of 7.65 m height and 0.25 m inner diameter. In the simulated experiments turbulence was generated and flame was accelerated with nine annular obstacles installed in the lower part of tube. The ignition point was located at the bottom flange of the facility.  All experiments were performed at ambient temperature and atmospheric pressure and differed by the initial hydrogen concentrations.

Presented simulations were performed using two-dimensional axisymmetrical grid with adiabatic wall assumption. A second order spatial discretization schemes were used. The solutions were tested over a range of significantly different grid resolutions in order to demonstrate grid-independent results.   Numerical results obtained with different turbulent flame speed correlations – Zimont, Bray and Bradley – were compared with each other and experimental results.  Furthermore, different turbulence models:  k-epsilon, k-omega and k-omega SST were applied. Different turbulence models led to different predictions of both the evolution of flame propagation and turbulence generation. 

Turbulent flame acceleration phase in the acceleration tube was well predicted. Furthermore, the simulations were able to capture the interaction between the flame and shock wave which was generated by the turbulent deflagration flame and reflected at the end of the ENACCEF2 tube. The overall numerical results show good agreement with the qualitative and quantitative behaviour of velocity results and flame front propagation.


Simulation of ENACCEF2 Premixed Hydrogen-Air Mixture Deflagration Experiment Using OpenFOAM

Division / Sponsors: 
Power Division & Nuclear Engineering Division (NED)

Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

International Conference on Nuclear Engineering
Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

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