Distinctive features of heat transfer on a permeable surface in a laminar compressible gas flow at Prandtl number Pr < 1

The laminar compressible boundary layer on a permeable plate with uniform injection is numerically investigated at Prandtl numbers Pr < 1. The calculations are performed at injected gas temperatures lower than that of an adiabatic impermeable wall. At a certain distance from the start of injection the temperature of the permeable wall becomes lower than the temperature of the injected gas. In this case, the temperature of the permeable wall passes through a minimum. This minimum shifts closer to the critical injection cross section with decreasing temperature of the injected gas, and at a certain injection temperature it coincides with it. For this case the critical temperature of the adiabatic permeable wall is introduced. For this quantity a criterial dependence on the Prandtl and Mach numbers is obtained, which allows to determine the critical temperature of the adiabatic permeable wall and estimate the injected gas temperature range when this effect can exist. (C) 2019 Elsevier Ltd. All rights reserved.