NUMERICAL STUDIES ON MACH FLOW CHARACTERISTICS OVER BACKWARD FACING ROUNDED STEP THROUGH HYBRID RANS-LES

Abstract

The fluid flow behaviour, involving density, vorticity and Mach number distributions, over a backward facing rounded step is studied by developing a 2D numerical model associated with the hybrid RANS-LES/SpalartAllmaras turbulent model, comprising a viscosity-like variable. The model incorporates fundamental issues like production, diffusion and destruction effects. Numerical simulations are performed with inflow free stream Mach number of 2.5 asociated with free stream pressure and velocity of 15350 N/m2 and 651.9 m/s2, respectively. The simulation results of density, vorticity and Mach number are noticed to be realistically even and also along the expected lines throughout the whole flow regime. It is found that both vorticity intensity and Mach number are relatively more at the expansion fan near the lip of the separation and near the reattachment shock, however, the fluid density is comparatively low at the same. It results in comparatively weak shock generations. In addition, it is also observed that the recirculation vicinity i.e. dead air region has attained the least fluid density, vorticity and the Mach number because of inviscid rotation. Furthermore, both density field and Mach number help us in getting whether the fluid flow is compressible or incompressible in behaviour. Above and beyond, the gradual change i.e. expansion/contraction within the flow field causes the vorticity generation resulting in relatively sound, smooth, flawless and favourable flow behaviours. Eventually, the recirculation vicinity is noticeably very small and due to this there is reduction in reattachment length.