Question

What should be the shape of the nozzle to achieve supersonic speed?

(a) Convergent

(b) Divergent

(c) Convergent-Divergent

(d) Divergent-Convergent

I got this question in final exam.

My doubt stems from Supersonic Nozzle Design topic in division Numerical Techniques for Nonlinear Supersonic Flow, Elements of Hypersonic Flow, Couette and Poiseuille Flow of Aerodynamics

Answer 1

Right choice is (c) Convergent-Divergent

The explanation: In order to achieve supersonic speed from rest we use a convergent divergent nozzle. This is because in the convergent section the flow is subsonic and is accelerated with decreasing cross-sectional area of the nozzle. The flow reaches sonic speed at the throat after which it is further accelerated in the divergent section as the supersonic flow increases with the increasing cross-sectional area of the nozzle.