Question

If area ratio is 1.110 then, at which mach number flow is flowing?

(a) 0.68

(b) 1.89

(c) 2

(d) 0.21

This question was addressed to me in an internship interview.

This question is from Propulsion topic in portion Propulsion and Fuel System Integration of Aircraft Design

Answer 1

Right answer is (a) 0.68

To explain: Given, area ratio A/A* = 1.110

Now, as we know, A/A* = (1/M)*(1+0.2M2)3*0.5787

For given problem, we will substitute different values of Mach number from the options.

Let’s consider M = 0.68

Hence, for assumed value of Mach number,

A/A* = (1/0.68)*(1+0.2*0.68^2)^3*0.5787

A/A* = 0.8510*1.09248^3 = 1.110.

The evaluated area ratio is equal to the given area ratio.

Hence, correct value of Mach number is 0.68.