Influence of surface sublimation on boundary layer stability at high Mach number

Abstract

Results of theoretical investigation of the linear stability properties of Mach 6 boundary layer on a flat-plate with sublimation coating are presented. Naphthalene (C 10 H 8) was chosen as a substance for such a coating. This is an organic compound capable to pure sublimation (phase transition from the solid state directly to gas, bypassing the melting stage) at moderate temperatures. Calculations performed on the basis of binary-mixture boundary-layer equations in the approximation of local self-similarity revealed that with increasing flow stagnation temperature the adiabatic surface temperature also increases that causes growth of mass flow rate of naphthalene evaporation. This leads to an increase in the density of the binary mixture (air and sublimation vapors) near the wall. The performed linear stability computations show that such a modification of the boundary layer profiles causes a reduction in the local linear amplification rates of perturbations of the first mode, while disturbances of the second mode are destabilized by the surface sublimation.