Question

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

(a) s1 = s2

(b) s1 > s2

(c) s1 < s2

(d) s1 s2 = 1

The question was asked in exam.

Asked question is from Compressible Flow through Diffusers topic in portion Compressible Flow through Nozzles, Diffusers and Wind Tunnels of Aerodynamics

Answer 1

Correct option is (c) s1 < s2

To elaborate: When the flow interacts with the oblique shock waves inside the supersonic diffuser, the flow diffuses to a slower velocity. This results in a normal shock wave at the end of the diffuser. Thus the exit entropy is higher than the entropy at the inlet section.