Question

What is the exit Mach number if the convergent nozzle is choked?

(a) 0

(b) 1

(c) 0.5

(d) 1.5

This question was addressed to me during an interview.

My question comes from Nozzles in section Quasi-One-Dimensional Flow of Aerodynamics

Answer 1

The correct choice is (b) 1

To explain I would say: In case of a convergent nozzle, when the flow is choked the exit Mach number is 1. In order to check if the nozzle is operating at choking conditions, we compare the actual pressure ratio to the critical pressure ratio. When the actual pressure ratio is larger than the critical pressure ratio, the nozzle is considered to be choked.