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Updated on 20th March, 2023 , 5 min read
The compressibility characteristics of fluid flow are measured by the Mach number; at a given Mach number, regardless of other variables, the fluid (air) behaves similarly when under the influence of compressibility. The International Standard Atmosphere predicts that the speed of sound is 340.3 meters per second (1,116.5 ft/s; 761.23 mph; 661.49 kn) in dry air at mean sea level with a standard temperature of 15 °C (59 °F). Since atmospheric temperature typically decreases with increasing altitude between sea level and 11,000 meters (36,089 ft), the speed of sound also tends to decrease as altitude increases. The speed of sound is not a constant; in a gas, it increases proportionally to the square root of the absolute temperature.
The ratio of flow velocity after the sound speed reaches a certain limit is known as the Mach number. Simply put, it is the ratio of a body's speed to the speed of sound in the medium around it.
The Mach number formula is-
M = u/c, where:
Although scientists who practice aerodynamics most of the time use these terms to describe a specific range of Mach values, speed below the speed of sound is referred to as subsonic, and speed above the speed of sound is referred to as supersonic.
The various Mach value regimes include:
Regime |
Subsonic |
Transonic |
Sonic |
Supersonic |
Hypersonic |
Hypervelocity |
Mach |
<0.8 |
0.8–1.3 |
1.0 |
1.3–5.0 |
5.0–10.0 |
>10.0 |
For supersonic and hypersonic flows, small disturbances spread downwind within a cone. The trigonometric sine of the cone angle b, which is equal to the inverse of the Mach number M, is the source of the Mach angle's name.
Regime |
Speed |
||||
(Mach) |
(knots) |
(mph) |
(km/h) |
(m/s) |
|
Re-entry speeds |
>25.0 |
>16,537 |
>19,031 |
>30,626 |
>8,508 |
High-hypersonic |
10.0–25.0 |
6,615–16,537 |
7,680–19,031 |
12,251–30,626 |
3,403–8,508 |
Hypersonic |
5.0–10.0 |
3,308–6,615 |
3,806–7,680 |
6,126–12,251 |
1,702–3,403 |
Supersonic |
1.3–5.0 |
794-3,308 |
915-3,806 |
1,470–6,126 |
410–1,702 |
Transonic |
0.8–1.3 |
530–794 |
609–914 |
980–1,470 |
273–409 |
Subsonic |
<0.8 |
<530 |
<609 |
<980 |
<273 |
When comparing the speed of any object with the speed of sound, the Mach number is a crucial factor. It is a parameter used to indicate how fast a flying object is moving through the air. It is widely used in fluid dynamics. To fully understand how airplanes and rockets move, the Mach number is extensively studied. It is a dimensionless quantity that, by definition, expresses the proportion of an object's velocity to the speed of sound.
Typically, the letter "M" is used to denote the Mach number.
Mach number is equal to (frac)(speed of sound/speed of object).
Where v is the object's velocity in relation to an internal or external boundary in a medium
and c equals the local medium's speed of sound.
The air molecules closest to an airplane's body are disturbed when it is in the air. When an airplane is moving at a higher speed, the air around it is compressed. By evaluating the Mach number, we can determine whether or not the fluid is compressible. Because it is the ratio of two velocities with the same dimensions, the Mach number has no dimensions.
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By - Nikita Parmar 2024-09-06 10:59:22 , 6 min readAns. As the speed exceeds the speed of sound, the flow is referred to as supersonic or hypersonic when the flight Mach number is greater than one M > 1.
Ans. The ratio of an object’s speed to the sound speed in a particular medium is known as its Mach number. So, Mach 1 is the speed of sound, which on an average day at sea level is approximately 761 mph.
Ans. A comparison between fluid flow rate and sound speed is made using the Mach number.
Ans. A new speed record of Mach 9.64 (10,240 km/h; 6,363 mph) was achieved by the X-43A at an altitude of about 33,500 m (110,000 ft), which also tested the vehicle’s capacity to withstand the heat loads present.
Ans. Approximately 6138 mph.