Turbulent hydrogen combustion modelling in experimental containment facilityHoller, Tadej (Avtor) Kljenak, Ivo (Mentor) nuclear safetyhydrogen combustionturbulent flame speedlaminar flame speededdy break-upHydrogen may be produced in a light water reactor nuclear power plant containment during a postulated severe accident. Ensuing hydrogen combustion, which is essentially inevitable, could inflict irreparable damage to the containment itself, resulting in a failure of the final protection barrier for the fission products release to the environment. Since the actual containment volumes surpass the volumes of even the largest available experimental facilities capable of conducting hydrogen combustion experiments for a few orders of magnitude, the computer-aided modelling presents itself as a formidable and accessible tool in this regard. Thus, use and development of reliable computational fluid dynamics modelling approaches for large-scale geometries is imperative for providing relatively cost-effective hydrogen combustion risk assessment. The present dissertation focuses on further theoretical investigation of hydrogen combustion, specifically hydrogen deflagration in large enclosures. This investigation is carried out through the development and validation of hydrogen combustion models and addresses some of the challenges on the way for the computer-aided modelling to become readily available for use in the real-scale containment dimensions. Specifically, it tackles the difficulties of available combustion models in producing the reliable predictions of the large-scale hydrogen deflagration experiments. The validation of combustion models was performed against the results obtained in two large-scale experimental facilities, i.e. THAI and HYKA-A2 experimental vessels. Firstly, a new combustion model was introduced, i.e. the extended eddy break-up (EEBU) model, which was developed from the existing less elaborate eddy break-up (EBU) model, with the additional treatment of the flame phenomenology also in the quasi-laminar combustion regime. This model retains beneficial characteristics of the EBU model, i.e. superior computational efficiency, while at the same time providing improved predictions for hydrogen deflagrations in the considered large-scale experiments. Furthermore, a novel approach was recommended undertaking a focused treatment of the laminar flame speed with the weighted laminar flame speed concept. This approach effectively balances the turbulent reaction rate with the buoyancy effects of the surrounding flow. It was applied to already existing extended turbulent flame speed closure (ETFC) model as well as to the newly introduced EEBU model. When properly executed, it proved to be extremely effective in improving the predictions of both models regarding the flame behavior in the considered large-scale hydrogen deflagration experiments.20192019-06-07 09:00:45Doktorsko delo/naloga107931sl