Question

A convergent-divergent nozzle is used in jet engines to

• A. Mix air and fuel in the combustor
• B. Compress incoming air at subsonic speeds
• C. Accelerate exhaust gases to supersonic speeds for high-speed flight
• D. Reduce engine noise

Hint:

For compressible flow, \[ \boxed{ \begin{aligned} \text{Convergent Nozzle} &\rightarrow M\le1 \text{Convergent-Divergent Nozzle} &\rightarrow M>1 \end{aligned} } \] Supersonic exhaust velocity produces higher thrust.

Answer 1

The Correct Option is C

Step 1: Recall the purpose of a convergent-divergent nozzle. A convergent-divergent (C-D) nozzle accelerates compressible flow. The flow reaches sonic speed at the throat and accelerates to supersonic speed in the diverging section.

Step 2: Identify its application in jet engines. The high-speed exhaust gases leaving the nozzle generate thrust. Thus, \[ \boxed{ \text{A C-D nozzle accelerates exhaust gases to supersonic speeds.} } \] Therefore, \[ \boxed{\text{Accelerate exhaust gases to supersonic speeds for high-speed flight}} \] is the correct answer. Thus, \[ \boxed{(C)} \] is the correct answer.