Question

Which of these processes is involved in slowing down the air inside the subsonic diffuser?

(a) Adiabatic compression

(b) Adiabatic expansion

(c) Isentropic expansion

(d) Isothermal compression

I have been asked this question in unit test.

My enquiry is from Compressible Flow through Diffusers topic in division Compressible Flow through Nozzles, Diffusers and Wind Tunnels of Aerodynamics

Answer 1

Right option is (b) Adiabatic expansion

Explanation: The process of slowing down the incoming flow inside the diffuser is done using adiabatic expansion. The pressure is constant throughout, if this was not the case then reduced total pressure in front of the compressor would yield less flow velocity.