Continuum Breakdown Effects on Surface Properties for Hypersonic Shock Wave-Boundary Layer Interaction

Abstract

Shock wave-boundary layer interaction (SWBLI) on the surface of hypersonic vehicles can lead to large surface-heating spikes which in turn impact vehicle design or flight envelopes. Accurate determination of SWBLI effects is therefore a potentially important element of hypersonic vehicle design, and high fidelity numerical modeling of SWBLI provides key advantages in the vehicle design cycle. One of the difficulties in hypersonic SWBLI simulation is the influence of continuum breakdown phenomena; such phenomena have been well documented for strong shocks and hypersonic boundary layers, but not specifically for SWBLI. In this work, we address various limitations in current engineering approaches for identification of continuum breakdown relevant to SWBLI flow problems. In particular, we present a new continuum breakdown criterion based on surface quantities which are determined using kinetic simulation techniques. A modification is then proposed to existing gradient-based breakdown criteria in order to resolve an inconsistency in Mach number dependence. The proposed breakdown criteria are assessed through comparison with an established criterion for a set of representative flat plate SWBLI problems, and for a type IV shock-shock interaction problem involving oblique shock impingement on the detached bow shock over a cylinder. This work is intended to demonstrate connections between continuum breakdown and gas properties along a surface, to reconsider Mach number dependence for gradient-based breakdown evaluation, and to determine the extent of continuum breakdown associated with SWBLI under representative hypersonic conditions.