Towards Direct Numerical Simulation of Hypersonic Transition Delay Via Distributed Wall Porosity

Abstract

The present manuscript outlines the progress made towards conducting a numerical analysis using three-dimensional direct numerical simulation (DNS) of transition to turbulence in a hypersonic boundary layer over a sharp cone, including the effects of acoustic energy absorption of a carbon/carbon (C/C) porous insert. Previous experimental studies proved the effectiveness of C/C in achieving hypersonic boundary layer transition delay and the current numerical study assesses its influence on high speed transition by modeling the C/C acoustic response as a complex impedance boundary condition (IBC). Simulations of a spatially developing boundary layer over a conical model, perturbed near the inflow by a pseudo-random forcing function, are performed with impermeable and porous walls. The current numerical scheme used is shown to be unstable after the appearance of the shocklets inside turbulent spots during transition and comparisons between results over impermeable and porous surfaces are made up to onset of transition. Nonetheless, the effectiveness of wall porosity in attenuating second-mode waves is demonstrated once again. The IBCs are also reactive to the three-dimensional overlying transitional turbulent flow, resulting in intense local regions of negative acoustic flux (i.e. acoustic energy leaving the domain), most likely associated with bursting events.