Question

What is the Mach number of the reflected wave if the velocity of the reflected wave is 600 m/s, velocity of induced mass motion is 350 m/s and the speed of air is 400 m/s?

(a) 3.5

(b) 2.375

(c) 1.25

(d) 3.561

I got this question in a job interview.

My question is taken from Reflected Shock Wave topic in division Unsteady Wave Motion of Aerodynamics

Answer 1

Right choice is (b) 2.375

For explanation: Given, WR = 600 \(\frac {m}{s}\), up = 350 \(\frac {m}{s}\), a2 = 400 m/s

The incident shock wave propagates into the gas ahead of it towards the wall with Mach number Ms which is reflected into the gas ahead of it with Mach number MR. This is given by the formula:

MR = \(\frac {W_R + u_p}{a_2}\)

Substituting the values, we get:

MR = \(\frac {600 + 350}{400}\) = 2.375