Search results
Results from the WOW.Com Content Network
The Mach number (M or Ma), often only Mach, (/ m ɑː k /; German:) is a dimensionless quantity in fluid dynamics representing the ratio of flow velocity past a boundary to the local speed of sound. [ 1 ] [ 2 ] It is named after the Austrian physicist and philosopher Ernst Mach .
Dimensionless numbers (or characteristic numbers) have an important role in analyzing the behavior of fluids and their flow as well as in other transport phenomena. [1] They include the Reynolds and the Mach numbers, which describe as ratios the relative magnitude of fluid and physical system characteristics, such as density, viscosity, speed of sound, and flow speed.
where a 0 is 1,225 km/h (661.45 kn) (the standard speed of sound at 15 °C), M is the Mach number, P is static pressure, and P 0 is standard sea level pressure (1013.25 hPa). Combining the above with the expression for Mach number gives EAS as a function of impact pressure and static pressure (valid for subsonic flow):
q is the dynamic pressure in pascals (i.e., N/m 2, ρ (Greek letter rho) is the fluid mass density (e.g. in kg/m 3), and; u is the flow speed in m/s. It can be thought of as the fluid's kinetic energy per unit volume. For incompressible flow, the dynamic pressure of a fluid is the difference between its total pressure and static pressure.
For a given Mach number, M 1, and corner angle, θ, the oblique shock angle, β, and the downstream Mach number, M 2, can be calculated. Unlike after a normal shock where M 2 must always be less than 1, in oblique shock M 2 can be supersonic (weak shock wave) or subsonic (strong shock wave). Weak solutions are often observed in flow geometries ...
This assumption is commonly made in engineering practice when the Mach number is less than about 0.3. C p {\displaystyle C_{p}} of zero indicates the pressure is the same as the freestream pressure. C p {\displaystyle C_{p}} of one corresponds to the stagnation pressure and indicates a stagnation point .
Mach number is more useful, and most high-speed aircraft are limited to a maximum operating Mach number, also known as M MO. For example, if the M MO is Mach 0.83, then at 9,100 m (30,000 ft) where the speed of sound under standard conditions is 1,093 kilometres per hour (590 kn), the true airspeed at M MO is 906 kilometres per hour (489 kn).
If the reservoir pressure is held constant and the receiver pressure reduced, the Mach number at the exit of the nozzle will increase until M e = 1 is reached, indicated by the left curve in figure 2. After M e = 1 is reached at the nozzle exit for p r = 0.5283p 0, the condition of choked flow occurs and the velocity throughout the nozzle ...