Detached Shock on:
[Wikipedia]
[Google]
[Amazon]
A bow shock, also called a detached shock or bowed normal shock, is a curved propagating disturbance wave characterized by an abrupt, nearly discontinuous, change in pressure, temperature, and density. It occurs when a
A bow shock, also called a detached shock or bowed normal shock, is a curved propagating disturbance wave characterized by an abrupt, nearly discontinuous, change in pressure, temperature, and density. It occurs when a supersonic flow
Choked flow is a compressible flow effect. The parameter that becomes "choked" or "limited" is the fluid velocity.
Choked flow is a fluid dynamic condition associated with the venturi effect. When a flowing fluid at a given pressure and temperatu ...
encounters a body, around which the necessary deviation angle of the flow is higher than the maximum achievable deviation angle for an attached oblique shock (see detachment criterion). Then, the oblique shock transforms in a curved detached shock wave. As bow shocks occur for high flow deflection angles, they are often seen forming around blunt bodies, because of the high deflection angle that the body impose to the flow around it.
The thermodynamic transformation across a bow shock is non-isentropic and the shock decreases the flow velocity from supersonic
Supersonic speed is the speed of an object that exceeds the speed of sound ( Mach 1). For objects traveling in dry air of a temperature of 20 °C (68 °F) at sea level, this speed is approximately . Speeds greater than five times ...
velocity upstream to subsonic
Subsonic may refer to:
Motion through a medium
* Any speed lower than the speed of sound within a sound-propagating medium
* Subsonic aircraft, a flying machine that flies at air speeds lower than the speed of sound
* Subsonic ammunition, a type o ...
velocity downstream.
Applications
The bow shock significantly increases thedrag
Drag or The Drag may refer to:
Places
* Drag, Norway, a village in Tysfjord municipality, Nordland, Norway
* ''Drág'', the Hungarian name for Dragu Commune in Sălaj County, Romania
* Drag (Austin, Texas), the portion of Guadalupe Street adj ...
in a vehicle traveling at a supersonic speed. This property was utilized in the design of the return capsules during space missions such as the Apollo program, which need a high amount of drag in order to slow down during atmospheric reentry
Atmospheric entry is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. There are two main types of atmospheric entry: ''uncontrolled entry'', such as the entr ...
.
Shock relations
As in normal shock and oblique shock, * The upstream static pressures is lower than the downstream static pressure. * The upstream static density is lower than the downstream static density. * The upstreamstatic temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
is lower than the downstream static temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
.
* The upstream total pressure is greater than the downstream total pressure.
* The upstream total density is lower than the downstream total density.
* The upstream total temperature is equal to the downstream total temperature, as the shock wave is supposed isenthalpic.
For a curved shock, the shock angle varies and thus has variable strength across the entire shock front. The post-shock flow velocity and vorticity can therefore be computed via the Crocco's theorem, which is independent of any EOS ( equation of state) assuming inviscid
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the inte ...
flow.
See also
* Bow shock * Gas dynamics * Moving shock * Prandtl–Meyer expansion fanReferences
* * {{cite book , last = Courant , first = R. , author2=Friedrichs, K.O. , title = Supersonic Flow and Shock Waves , origyear = 1948 , publisher = Interscience Publishers , location = New York , year = 1956 Aerodynamics Shock waves