Overview

In Sub-Section 4.3.1 we have seen that if the Reynolds number characterizing a flow field is large enough, we can separate the flow field into inviscid and viscous portions. From Fig. 2.3, Section 2.1, we gather that the unit Reynolds numbers in the flight domain of interest are indeed sufficiently large. This does not mean that aerodynamic properties of hypersonic vehicles can be prescribed fully by means of inviscid theory. This is at best possible for the longitudinal movement of re-entry vehicles.

At transonic, supersonic and hypersonic flight we observe the important phenomenon of shock waves. The shock wave is basically a viscous phenomenon, but in general can be understood as a flow discontinuity embedded in an inviscid flow field. In this chapter we look at shock waves as compressibility phenomena occurring in the flow fields past hypersonic flight vehicles. We treat their basic properties, and also the properties of the isentropic Prandtl-Meyer expansion. Of importance in hypersonic flight-vehicle design is the stand-off distance of the bow-shock surface at blunt vehicle noses. We investigate this phenomenon as well as the effects of entropy-layer swallowing by the vehicle boundary layers.

Also of interest for the development of boundary layers is the change of the unit Reynolds number across shock waves. We will see that an increase of the unit Reynolds number will only occur, if the shock wave is sufficiently oblique. Then a boundary layer behind a shock wave close to the body surface will be thinned. This subsequently changes...