ABSTRACT
Shock waves arise when there are parts of the fluid that have velocities greater than the characteristic wave speeds, so that information about changes in the flow travels too slowly to influence the flow ahead of the shock. This chapter discusses the conditions that must apply for the shock to endure for any significant period of time: a small disturbance must not lead to disruption of the shock. It considers the reflection, refraction, and transmission of a wave incident on the shock. This process is greatly complicated by the fact that the motion of the medium relative to the shock may be greater than the wave velocity. In the shock frame, each characteristic wave is propagated either towards or away from the shock. Apart from the entropy wave, these characteristic waves occur in pairs, a pair each of transverse Alfven waves, slow waves, and fast waves.
