Читать книгу Fundamentals of Heat Engines - Jamil Ghojel - Страница 54

Examples include flow in ducts, nozzles, and diffusers without heat transfer and work being done. Knowing , where a is the speed of sound and M_a is the Mach number at the inlet, and rewriting Eq. (1.64) as

we obtain

Also,

Combining the last two equations, we get

(1.67)

From Eqs. (1.48) and (1.67)

(1.68)

The pressure ratio for M_a = 1 at γ = 1.4 is equal to 1.893. This is the critical pressure ratio for air. To achieve supersonic flow, the stagnation pressure needs to be such that p_t > 1.893p.