Mach wave

A Mach wave is a pressure disturbance traveling at the speed of sound, caused by a disturbance moving at supersonic speed through a fluid. Unlike a shock wave, which is an abrupt and finite change in pressure and density, a Mach wave represents an infinitesimally small pressure disturbance.

These waves can occur when an object moving through a fluid (like air) reaches a speed equal to or greater than the speed of sound in that fluid. As the object moves faster than the pressure waves it creates, these waves cannot propagate ahead of the object. Instead, they pile up, forming a cone-shaped region of increased pressure trailing behind the object.

Each point on the surface of the supersonic object acts as a source of pressure disturbances. These individual disturbances propagate outward as spherical waves. The envelope of all these spherical waves forms the Mach cone. The angle between the Mach cone and the direction of motion is called the Mach angle, and it is mathematically related to the Mach number (the ratio of the object's speed to the speed of sound). A higher Mach number results in a smaller Mach angle.

Mach waves are often studied in the context of aerodynamics and fluid dynamics to understand supersonic flow behavior. They can be visualized using techniques like Schlieren photography or shadowgraphy, which are sensitive to changes in density. While individually weak, Mach waves can interact with each other or with surfaces, potentially leading to the formation of stronger shock waves. They are crucial in analyzing the flow patterns around supersonic aircraft and projectiles.