Slip effects on the stability of supersonic laminar flat plate boundary layer

Current worldwide efforts to develop maneuverable vehicles flying in rarefied gas hypersonic environments require quantification of laminar-turbulent transition in the hypersonic boundary layers formed on lifting surfaces and control fins. The present contribution commences efforts to document the effect of wall-slip velocity and temperature distributions on the linear stability of hypersonic laminar boundary layers developing on a semi-infinite flat plate, for Knudsen numbers kn ∼ O(0.05), corresponding to flight altitudes of 35km ≤ ℎ ≤ 65km and, at first instance, low Reynolds numbers, Re∼ O(10³ − 10⁴ ). The steady laminar base flow is obtained using the Direct Simulation Monte Carlo (DSMC) method. Results on the mean-free-path and wall-normal velocity and temperature gradients obtained are used to construct slip-velocity and temperature-jump boundary conditions along the plate surface, following recent updates of the Maxwell / von Smoluchowski theory. Linear stability analysis of the DSMC profiles extracted from the simulation and those obtained by the updated compressible boundary layer theory reveals quantitative but not qualitative differences on the characteristics of the leading flow eigenmodes over the range of parameters examined. Work is underway to characterise whether the observed differences are a result of a residual pressure gradient present in the DSMC simulation, or intrinsic to kinetic fluctuations unaccounted for in the framework of Navier-Stokes/boundary layer theory.