Analysis of nonequilibrium effects characterizes shock wave-boundary layer interactions in hypersonic flow

Flight at hypersonic speeds generates strong shock waves. Hypersonic vehicle design requires a solid understanding of the interaction of these shock waves with the vehicle boundary layer due to its influence on aerothermodynamic load. As a result, much research in the last several decades has focused on hypersonic shock wave-boundary layer interactions for both laminar and turbulent boundary layers.

A new article looks closely at nonequilibrium effects in hypersonic laminar, shock wave-boundary layer interactions with a combination of time-accurate direct simulation Monte Carlo (DSMC) calculations, linear global instability analysis and momentum potential theory. It represents the first time such a hybrid approach has been used to characterize unsteady Edney type IV flows that cause bow and separation shock waves.

Previously, the authors presented time accurate DSMC simulations of shock-dominated hypersonic laminar flows over a double cone. In the present work, they wanted to see how the disturbances would change as a function of Reynolds number and analyze the mechanisms that cause unsteadiness in shock wave-laminar boundary layer interactions.

They first modeled the base flow with DSMC in a time-dependent manner. Then they used linear global instability analysis and momentum potential theory (MPT) to investigate the nature of the disturbances and how they might change with Reynolds number.

The results revealed global modes at a Mach number of 16 and how they depended on Reynolds number. Additional Fourier-based analysis showed agreement with experiments and direct numerical simulations of Strouhal numbers — which describe oscillating flow mechanisms — for an Edney type IV flow. Surprisingly, they also observed lambda shocklets in the amplitude functions. These demonstrated, for the first time using DSMC coupled with MPT, the interplay between shock oscillation and laminar separated flow global instability.

Source: “On the unsteadiness of shock-laminar boundary layer interactions of hypersonic flows over a double cone,” by Ozgur Tumuklu, Vassilis Theofilis, and Deborah A. Levin, Physics of Fluids (2018). The article can be accessed at https://doi.org/10.1063/1.5047791 .