Numerical assessment of confinement effect and flow structure in case of hydrogen release in a two-vented cavity

We present numerical results from direct numerical simulations (DNS) of an air-helium buoyant jet in a two-vented cavity. Geometrical configuration of the cavity is chosen to ensure a bi-layer stratification distribution of helium, which is commonly assumed in relevant industrial models. A series of computations with different horizontal sizes of cavity is performed to determine the optimal dimensions, for which the helium buoyant jet and the top mixture layer are not influenced by the end walls. Results are analysed in terms of flow structure and helium concentration distribution, but also of inlet mass flux of fresh air and of helium outlet flux, as fluxes are kept free through the vents. Additionally, buoyancy flux in the jet corresponding to Morton’s theory (1956) is calculated to deduce entrainment coefficient and compared with literature.