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When an aircraft exceeds Mach 1 (i.e. the sound barrier), a large pressure difference is created just in front of the aircraft. This abrupt pressure difference, called a shock wave , spreads backward and outward from the aircraft in a cone shape (a so-called Mach cone ).
The Mach angle is acute, showing that the body exceeds Mach 1. The angle of the Mach wave (~59 degrees) indicates a velocity of about Mach 1.17. In fluid dynamics, a Mach wave, also known as a weak discontinuity, [1] [2] is a pressure wave traveling with the speed of sound caused by a slight change of pressure added to a compressible flow.
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).
This occurs typically somewhere between Mach 0.8 and Mach 1.2. Sounds are traveling vibrations in the form of pressure waves in an elastic medium. Objects move at supersonic speed when the objects move faster than the speed at which sound propagates through the medium.
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.
In aerodynamics, the normal shock tables are a series of tabulated data listing the various properties before and after the occurrence of a normal shock wave. [1] With a given upstream Mach number, the post-shock Mach number can be calculated along with the pressure, density, temperature, and stagnation pressure ratios. Such tables are useful ...
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The minimum pressure ratio may be understood as the ratio between the upstream pressure and the pressure at the nozzle throat when the gas is traveling at Mach 1; if the upstream pressure is too low compared to the downstream pressure, sonic flow cannot occur at the throat.