A new two-fluid model averaging in the near-wall region is proposed to ensure consistent matching of the two-phase k–ε turbulence model with the two-phase logarithmic law of the wall (Marie J. L., Moursali, E., and Tran-Cong, S., 1997, “Similarity Law and Turbulence Intensity Profiles in a Bubbly Boundary Layer,” Int. J. Multiphase Flow, 23(2), pp. 227–247). The void fraction distribution obtained with the averaging procedure is seen to conform to the two-phase wall function approach which is based on a double step function void fraction distribution. In particular, the proposed averaging technique is shown to achieve grid convergence in the near-wall region, which could not be obtained otherwise. Computational fluid dynamics (CFD) results with the proposed technique are in good agreement with experiments on upward bubbly flows over a flat plate, and upward and downward flows in pipes. An additional advantage of the proposed technique is that it replaces the wall force model, which has a significant degree of uncertainty in turbulent flow modeling, with a simpler geometric constraint.
The management of hydrogen in nuclear reactor containment after LOCA is of practical importance to preserve the structural integrity of the containment. This paper presents the results of systematic work carried out using the commercial software FLUENT to assess the concentration distribution of hydrogen in a typical Indian Nuclear Reactor Containment. Accurate turbulence modelling is important to predict the concentration distribution correctly. The turbulence models which were most commonly cited in the literature for modelling buoyancy driven flows were assessed for their suitability and it was found that the buoyancy modified Standard k-ε model is adequate for the purpose by comparing with some experimental data available in the literature. Subsequently, unstructured meshes were generated to represent the containment of a typical Indian nuclear reactor. Analyses were carried out to quantify the hydrogen distribution for three cases. These were (1) Uniform injection of hydrogen for a given period of time at room temperature, (2) Time varying injection as has been computed from an accident analysis code, (3) Time varying injection (as used in case (2)) at a high temperature. A parametric exercise was also carried out in case (1) where the effect of various inlet orientations and locations on hydrogen distribution was studied. Results of all these cases have been presented in this paper.
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