Question

The figure shows schematics of wave patterns at the exit of nozzles A and B operating at different pressure ratios.

Nozzles A and B, respectively, are said to be operating in: 

• A. over-expanded mode and under-expanded mode
• B. under-expanded mode and perfectly expanded mode
• C. perfectly expanded mode and under-expanded mode
• D. under-expanded mode and over-expanded mode

Hint:

Shocks at the exit imply over-expansion; expansion fans imply under-expansion in supersonic nozzles.

Answer 1

The Correct Option is A

Step 1: Examine Nozzle A.
In Nozzle A, oblique shocks are seen at the nozzle exit. Shocks indicate that the exit pressure is higher than the ambient pressure. This situation occurs when the nozzle is operating in an over-expanded condition, causing the flow to compress through shock waves.

Step 2: Examine Nozzle B.
In Nozzle B, only expansion fans appear at the exit. Expansion waves occur when the exit pressure is greater than the ambient pressure. This means the nozzle is operating in an under-expanded mode, allowing further expansion after exiting the nozzle.

Step 3: Conclusion.
Therefore, Nozzle A is over-expanded and Nozzle B is under-expanded.

Final Answer: (A) over-expanded mode and under-expanded mode