Question

Which of these conditions is not applicable for choked flow?

(a) The Mach number at the throat is zero

(b) Mass flow is constant

(c) Exit pressure is lower than inlet pressure

(d) Exit pressure is same as the inlet pressure

This question was addressed to me in a job interview.

My question comes from Governing Equations for Quasi One Dimensional Flow in section Compressible Flow through Nozzles, Diffusers and Wind Tunnels of Aerodynamics

Answer 1

The correct option is (d) Exit pressure is same as the inlet pressure

Best explanation: Choked flow is a condition where the exit pressure is lower than inlet pressure to a point where the flow after throat section becomes frozen. After this, despite lowering the value of exit pressure, inlet pressure has no effect. The mass flow remains constant despite reducing the exit pressure.