THE EFFECT OF SURFACE-EVAPORATION KINETICS ON THE SUBLIMATION INTO A BOUNDARY LAYER
RAND CORP SANTA MONICA CA
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The behavior of the laminar binary boundary layer with blowing is coupled with the kinetic-evaporation-rate law of the surface material. It is found that the solution of this combined problem exhibits an asymptotic behavior at large Reynolds number which is identified with the usual near-equilibrium solution in which the vapor near the wall is very nearly in thermodynamic phase change equilibrium. However, the near equilibrium solution is invalid in a region near the origin of the boundary layer, which is characterized by a length formed with physical parameters describing the basic flow and the surface properties. In this region, which is treated here approximately, the blowing parameter decreases to zero, the wall temperature increases, and the sublimation rate tends to an upper limit as the origin of the boundary layer is approached. The principal result of the analysis is the estimation of the length of the region of transition to the near-equilibrium solution. This length is an independent characteristic of the problem and does not scale as do the boundary- layer properties that is, with the Reynolds number. This implies that while the transitional length on typical re-entry vehicles is small and probably negligible unless the leading edge is very sharp, practical windtunnel test models can easily be affected over most of their chord.