Читать книгу Fundamentals of Heat Engines - Jamil Ghojel - Страница 33

The acoustic velocity of a fluid is the speed of sound in the fluid under isentropic conditions and is given by

(1.33)

For a gas of molecular mass μ_f, , where is the universal gas constant (=8314.4 J/kmole K).

Rewriting Eq. (1.33) in terms of the universal gas constant ,

(1.34)

At a given temperature and ratio of specific heats, the acoustic velocity can be written as

The Mach number M_a (in honour of Ernst Mach) is defined as

(1.35)

The Mach number is used to indicate speed of flow or forward speed of aircraft and rockets and also to indicate different flow regimes:

Mach number	Flow regime
Ma < 1	Subsonic flow
Ma = 1	Sonic flow
1 < Ma < 5	Supersonic flow
Ma > 5	Hypersonic flow