Question

Up to which Mach number is Prandtl – Glauert rule applicable for subsonic flow?

(a) 1

(b) 0.5

(c) 0.8

(d) 0.65

The question was asked in class test.

Query is from Linearized Subsonic Flow topic in division Linearized and Conical Flows of Aerodynamics

Answer 1

Right answer is (c) 0.8

To elaborate: For an increasing Mach number in a subsonic flow over a body, the coefficient of pressure also increases as a result of Prandtl – Glauert rule. But, after Mach number 0.8 the equation fails because the flow enters transonic regime where coefficient of pressure tends to infinity as Mach number tends to unity.