# Mach number

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Related to Mach number: Drag divergence Mach number

## Mach number

(mäk) [for E. MachMach, Ernst
, 1838–1916, Austrian physicist and philosopher, b. Moravia. He taught (1864–67) mathematics at Graz and later, until his retirement in 1901, was professor of physics at Prague and Vienna.
], ratio between the speed of an object and the speed of sound in the medium in which the object is traveling. An airplane that has the velocity of Mach 3.0 is traveling at three times the speed of sound as measured in the prevailing atmospheric conditions.

## Mach number

In the flow of a fluid, the ratio of the flow velocity, V, at a given point in the flow to the local speed of sound, a, at that same point. That is, the Mach number, M, is defined as V/a. In a flowfield where the properties vary in time and/or space, the local value of M will also vary in time and/or space. In aeronautics, Mach number is frequently used to denote the ratio of the airspeed of an aircraft to the speed of sound in the freestream far ahead of the aircraft; this is called the freestream Mach number. The Mach number is a convenient index used to define the following flow regimes: (1) subsonic, where M is less than 1 everywhere throughout the flow; (2) supersonic, where M is greater than 1 everywhere throughout the flow; (3) transonic, where the flow is composed of mixed regions of locally subsonic and supersonic flows, all with local Mach numbers near 1, typically between 0.8 and 1.2; and (4) hypersonic, where (by arbitrary definition) M is 5 or greater.

Perhaps the most important physical aspect of Mach number is in the completely different ways that disturbances propagate in subsonic flow compared to that in a supersonic flow. Shock waves are a ubiquitous aspect of supersonic flows. See Compressible flow, Shock wave, Sonic boom

## Mach Number

a fundamental characteristic of a gas flow, equal to the ratio of the velocity of the flow v to the velocity of sound a at the same point in the flow: M = v/a. For a body moving in a gas, the Mach number is equal to the ratio of the velocity of the body to the velocity of sound in the medium.

Named after E. Mach, the Mach number is also one of the fundamental criteria of aerodynamic similarity for cases in which the compressibility of the gas cannot be disregarded. In air the compressibility must be taken into account for velocities v > 100 m/sec, to which the number M > 0.3 corresponds. For M < 1, the flow is called subsonic; for M = 1, sonic; and for M > 1, supersonic. One of the principal features of supersonic flow is the formation of shock waves in the flow around bodies or on braking the gas flow. Wave drag, which increases with the Mach number, arises in shock waves as a result of the dissipation of energy. Flow regions with M > 5 (hypersonic flows) have a number of unique features; in particular, physicochemical changes in a gas compressed in a shock wave become significant.

M. IA. IUDELOVICH

## Mach number

[′mäk ‚nəm·bər]
(fluid mechanics)
The ratio of the speed of a body or of a point on a body with respect to the surrounding air or other fluid, or the ratio of the speed of a fluid, to the speed of sound in the medium. Symbolized NMa . Also known as relative Mach number.

## Mach number

The ratio of the velocity of a body to that of sound in a surrounding medium. A Mach number of 0.8 or 1.2 means that the aircraft is flying at 0.8 or 1.2 times, respectively, the local speed of sound at that ambient temperature. Also known as a relative Mach number.

## Mach number

the ratio of the speed of a body in a particular medium to the speed of sound in that medium. Mach number 1 corresponds to the speed of sound
References in periodicals archive ?
For example, the corresponding aerodynamic outputs of the system under the same FWGN excitation for the mean angle of attack [[alpha].sub.0*], and Mach number [M.sub.[infinity]*] can be written as
Figure 3c) shows the [c.sub.z] of two NACA 0012 airfoils crossing over time traveling at an angle of attack for 7[degrees], separated by 2.33 ft (S/c = 6.21), while comparing Mach numbers of 0.47 and 0.90.
With an increase in the area ratio of the C-D nozzles, from 4 to 16, the exit Mach number became even more supersonic.
The threshold Alfven Mach number being equal to 2.359305 determines a critical flow velocity of 825.8km [s.sup.-1] for KH instability onset which is much higher than the jet #16 speed of 532 km [s.sup.-1].
To sum up, the linear aerodynamic theory shows similar results for various Mach numbers, whereas, with the nonlinear aerodynamic theory, a larger Mach number produces a lower panel positive deflection peak.
The following figures represent the pressure and velocity for multiple ramp inlet models at the Mach Number 8.
where [bar.M] is the cross-section average Mach number. Due to the acoustic impedance of the lined wall, the acoustic energy is absorbed at the wall.
The aerodynamic coefficients and the distance of aerodynamic center are all a function of local Mach number at the mass center of the projectile.
The only disadvantage of the scheme is that it does not work in very low Mach number flow.
In a 26-inch fully retracted aft position, at the design cruise Mach number of 3.2, an oblique shock system exists with the lead shock stretched between the cone's apex and the nacelle lip, to yield a maximum total pressure recovery of 40:1.
The operating Mach number is usually less than 0.8 for a subsonic cascade, but can go up to 2.0 and more at the tip of a transonic blade assembly.
Everything was in knots, nautical miles and Mach number. During combat tours in Vietnam we got used to kilometers, but miles and miles per hour never left us.

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