Question

What is the relation between the nozzle A1t and diffuser throat area A2t in the supersonic wind tunnel?

(a) At2 = At1

(b) At2 > At1

(c) At2 < At1

(d) At2 At1 = 1

The question was asked by my college professor while I was bunking the class.

My question is taken from Supersonic Wind Tunnels topic in chapter Compressible Flow through Nozzles, Diffusers and Wind Tunnels of Aerodynamics

Answer 1

Correct answer is (b) At2 > At1

The best I can explain: The relation between the throat areas in terms of total pressure is given by:

\(\frac {A_{t2}}{A_{t1}} = \frac {p_{01}}{p_{02}}\)

Since in the diffuser section, the total pressure drops across oblique shock wave, thus p02 < p01. Hence the throat area of the diffuser is larger than the throat area of the nozzle.