Question

How is diffuser throat area At2 related to the nozzle throat area At1?

(a) At2 = At1

(b) At2 > At1

(c) At2 < At1

(d) At2 At1 = 1

I have been asked this question by my school teacher while I was bunking the class.

This intriguing question originated from Compressible Flow through Diffusers in chapter Compressible Flow through Nozzles, Diffusers and Wind Tunnels of Aerodynamics

Answer 1

Correct option is (b) At2 > At1

Explanation: There are two throats in the supersonic wind tunnel. The first is that of the nozzle and the second is that of the diffuser. The nozzle’s throat region is equal to A * (sonic area) and the diffuser’s throat area is greater than the nozzle’s throat area because of the rise in entropy within the diffuser.