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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. =, where: M is the local Mach number,
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):
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.
Conversion of the Mach unit of speed depends on the altitude at which the speed is measured. That altitude should be specified either in feet (for example, |altitude_ft=10,000 ) or in metres (for example, |altitude_m=3,749 ).
is the standard gravity (in m/s 2 or ft/s 2). In rockets, due to atmospheric effects, the specific impulse varies with altitude, reaching a maximum in a vacuum. This is because the exhaust velocity is not simply a function of the chamber pressure, but is a function of the difference between the interior and exterior of the combustion chamber .
The critical Mach number (Mcrit) is lowest free stream Mach number at which airflow over any part of the aircraft first reaches Mach 1. So the subsonic speed range includes all speeds that are less than Mcrit. All commercial aircraft — Transonic [0.8–1.2) 614–921 mph (988–1,482 km/h; 274–412 m/s)
TAS can be calculated as a function of Mach number and static air temperature: =, where is the speed of sound at standard sea level (661.47 knots (1,225.04 km/h; 340.29 m/s)),
= 0.514 77 3 m/s mach number: M: Ratio of the speed to the speed of sound [note 1] in the medium (unitless). ≈ 340 m/s in air at sea level ≈ 295 m/s in air at jet altitudes metre per second (SI unit) m/s ≡ 1 m/s = 1 m/s mile per hour: mph ≡ 1 mi/h = 0.447 04 m/s: mile per minute: mpm ≡ 1 mi/min = 26.8224 m/s: mile per second: mps ≡ ...