Question

In case of flow inside a nozzle, how should the exit pressure be in relation to the inlet pressure?

(a) Exit pressure = Inlet pressure

(b) Exit pressure > Inlet pressure

(c) Exit pressure < Inlet pressure

(d) There is no relation between the two pressures

The question was posed to me in quiz.

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

Answer 1

Correct answer is (c) Exit pressure < Inlet pressure

The best I can explain: The air in the nozzle will never flow by itself considering that the area ratio between the inlet and the throat is very high. There needs to be a pressure difference created for the air to move. This happens only when the exit pressure is less than the the inlet pressure (pe < p0).