Question

What is the entropy relation between the entry and exit of an actual diffuser?

(a) s1 = s2

(b) s1 > s2

(c) s1 < s2

(d) s1 s2 = 1

The question was asked in an online quiz.

I'm obligated to ask this question of Quasi-One-Dimensional Flow Diffusers in portion Quasi-One-Dimensional Flow of Aerodynamics

Answer 1

The correct answer is (c) s1 < s2

The explanation is: The flow diffuses to a slower velocity when the flow interacts with the oblique shock waves inside the diffuser. This causes the diffuser to have a normal shock wave at the end. The entropy of the exit is therefore higher than the entropy of the inlet segment.