Shock waves I/II

The subject of this lecture is related to shock wave phenomena. In general, a shock wave represents a compression wave travelling at supersonic speed relative to the undisturbed flow. Shock waves occur in gaseous, liquid as well as solid materials. This lecture only considers the propagation in gases. A shock wave represents a nearly perfect discontinuity of the flow parameters, the thickness of the wave amounts to a few molecular mean free pathes. Airplanes flying at supersonic speed generate shock waves, they occur in some intakes of jet propulsion engines, in supersonic compressors, at sudden pressure release of pressurized volumes, during explosions, et cetera.

After introduction of the conservation equations for steady flow, the general shock relations will be shown where the possibility of expansion shocks is also included. Further, a shock wave is considered moving at constant speed and the reflection process of this wave at a solid wall. The influence of non-perfect gas behaviour at high temperatures is also discussed. According to shock waves next the propagation behaviour of expansion waves is described as well as the wave processes occurring in a shock tube and for different wave interactions. The influence of boundary layer effects on this ideal shock tube flow ends this chapter. For two-dimensional flow the general fundamentals of oblique shocks and of the special case of Mach reflection are given.