Question

Which of these factors contribute to additional total pressure losses inside the oblique shock diffuser?

(a) Abrupt change of convergent – divergent sections

(b) Shock wave interaction with walls

(c) Isentropic flow

(d) Presence of normal shock

The question was posed to me at a job interview.

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

Answer 1

Right answer is (b) Shock wave interaction with walls

The explanation is: In real life, oblique shock diffusers have viscous flow. The presence of shock waves inside the diffuser leads to interaction with the viscous boundary layer of the diffuser walls which leads to additional pressure losses. There’s also friction involved which makes oblique shock diffusers far from the ideal diffusers which have no total pressure losses.