High-altitude aerothermodynamics

Hypersonic high-altitute flight can be conventionally divided into three regimes: the continuum regime, when the Knudsen number Kne1, the free-molecule regime (Kn⪼1), and the transitional regime (K∼1). In general, each of these regimes differs with respect to both the structure of the flow and the method of determining the aerodynamic and thermal characteristics. For Knudsen numbers Kne1 the Navier-Stokes equations or models with slip and temperature jump boundary conditions are widely used. When Kn⪼1 the methods employed are mainly directed towards determining the distribution function of the molecules reflected from the surface of the body. On the transition interval between these two limiting regimes numerical methods of solving the Boltzmann equation and its model equations are being used with success. Together with the experimental techniques, these various methods, which complement each other, make it possible to investigate gas flows fairly effectively from the continuum to the free-molecule regime (see, for example, [1]).