Shock wave

The sonic boom associated with the passage of a supersonic aircraft is a type of sound wave produced by constructive interference.

This change in the matter's properties manifests itself as a decrease in the energy which can be extracted as work, and as a drag force on supersonic objects; shock waves are strongly irreversible processes.

In a shock wave the properties of the fluid (density, pressure, temperature, flow velocity, Mach number) change almost instantaneously.

[7] Measurements of the thickness of shock waves in air have resulted in values around 200 nm (about 10−5 in),[8] which is on the same order of magnitude as the mean free path of gas molecules.

In reference to the continuum, this implies the shock wave can be treated as either a line or a plane if the flow field is two-dimensional or three-dimensional, respectively.

Shock waves are formed when a pressure front moves at supersonic speeds and pushes on the surrounding air.

The sound wave is heard as the familiar "thud" or "thump" of a sonic boom, commonly created by the supersonic flight of aircraft.

At such control surfaces, momentum, mass flux and energy are constant; within combustion, detonations can be modelled as heat introduction across a shock wave.

In these cases, the 1d flow model is not valid and further analysis is needed to predict the pressure forces which are exerted on the surface.

To produce a shock wave, an object in a given medium (such as air or water) must travel faster than the local speed of sound.

Strong shocks in rapid dense granular flows can be studied theoretically and analyzed to compare with experimental data.

Consider a configuration in which the rapidly moving material down the chute impinges on an obstruction wall erected perpendicular at the end of a long and steep channel.

Impact leads to a sudden change in the flow regime from a fast moving supercritical thin layer to a stagnant thick heap.

In memristors, under externally-applied electric field, shock waves can be launched across the transition-metal oxides, creating fast and non-volatile resistivity changes.

A strong expansion wave or shear layer may also contain high gradient regions which appear to be a discontinuity.

In fact, correct capturing and detection of shock waves are important since shock waves have the following influences: (1) causing loss of total pressure, which may be a concern related to scramjet engine performance, (2) providing lift for wave-rider configuration, as the oblique shock wave at lower surface of the vehicle can produce high pressure to generate lift, (3) leading to wave drag of high-speed vehicle which is harmful to vehicle performance, (4) inducing severe pressure load and heat flux, e.g. the Type IV shock–shock interference could yield a 17 times heating increase at vehicle surface, (5) interacting with other structures, such as boundary layers, to produce new flow structures such as flow separation, transition, etc.

Schlieren photograph of an attached shock on a sharp-nosed supersonic body
USS Iowa firing at broadside during training exercises in Puerto Rico, 1984. Circular marks are visible where the expanding spherical atmospheric shockwaves from the gun firing meet the water surface.
Pressure–time diagram at an external observation point for the case of a supersonic object propagating past the observer. The leading edge of the object causes a shock (left, in red) and the trailing edge of the object causes an expansion (right, in blue).
Conical shockwave with its hyperbola-shaped ground contact zone in yellow
Shock wave propagating into a stationary medium, ahead of the fireball of an explosion. The shock is made visible by the shadow effect (Trinity explosion).
Schlieren photograph of the detached shock on a bullet in supersonic flight, published by Ernst Mach and Peter Salcher in 1887
Shadowgram of shock waves from a supersonic bullet fired from a rifle. The shadowgraph optical technique reveals that the bullet is moving at about a Mach number of 1.9. Left- and right-running bow waves and tail waves stream back from the bullet and its turbulent wake is also visible. Patterns at the far right are from unburned gunpowder particles ejected by the rifle.
Damage caused by a meteor shock wave
Recompression shock on a transonic-flow airfoil, at and above critical Mach number
Interacting shockwaves from two supersonic planes
NASA took their first Schlieren photograph of shock waves interacting between two aircraft in 2019.