Shock waves are the pressure waves caused by a moving body when the speed of the body approaches the local speed of the sound in that fluid. As the body approaches the speed of sound, the wave fronts caused by it approach its maximum speed (which is the speed of sound) and stack up in the front of the body or source as a barrier, most commonly referred to as a sound barrier. When the body accelerates and travels faster than the speed of sound, breaking the sound barrier, the stacked wave fronts travel along with the body as shock waves. There is a rapid change in the density, pressure and temperature in the medium due to the formation of shock waves. This pressure difference is what leads to the sonic boom. Sometimes the rapid decrease in the temperature of the medium behind the shock wave creates a local area of rapid condensation, leading to the formation of clouds around a supersonic body like an aircraft. It is known as vapor cone.
Frequently Asked Questions
How are shockwaves photographed?
Shock waves create a rapid change in density of the medium behind it. Light refracts according to the varying density around as it propagates. This light refraction through the density gradient can be photographed using one of the optical flow visualization techniques like the shadowgraph or the similar Schlieren photography.
What is an expansion fan?
Expansion fan is a type of phenomena observed when a supersonic flow propagates around a convex corner. The flow causes the formation of an infinite number of Mach waves and forms a region of waves at the corner. As the area is expanded, these waves are called as the expansion waves or Prandtl-Meyer expansion fan. The expansion waves result in turning the supersonic inlet flow and accelerating it through the Mach wave regime.