In which of the following cases is the effect of the boundary layer more pronounced?

Longer nozzles with low area ratios

Longer nozzles with high area ratios

Shorter nozzles with low area ratios

Shorter nozzles with high area ratios

Correct Answer : Longer nozzles with high area ratios

Explanation : In longer nozzles with high area ratios, a relatively higher proportion of mass flow is found to be lying within the low-velocity region of the boundary layer. When that happens, the boundary layer plays a significant role in reducing the performance of the rocket engine.

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Assertion : Oxygen addition in the control flow gases of solid rocket engine will result in a higher characteristic velocity of the exit jet.
Reason : Because of secondary combustion, stagnation temperature and pressure increase. Higher stagnation temperature results in exhaust jet characteristic velocity.

Both assertion and reason are correct

Both assertion and reason are wrong

The assertion is wrong but the reason is correct

The assertion is correct but the reason is wrong

Correct Answer : Option (A) : Both assertion and reason are correct

Explaination : Usually solid propellant combustion gases are fuel rich and addition of oxygen into this control flow results in a secondary combustion. It increases both stagnation temperature and pressure of the flow. Because of pressure sensitivity on burning rate, higher stagnation pressure results in a higher mass flow rate, while the increase in stagnation temperature results in an increase in the characteristic velocity of the exit jet.

Which of the following thrust modulation technique makes use of symmetric injection for jet area control?

Shock Vectoring Control

Shock Thrust Modulation

Scarfed Nozzle Thrust Modulation

Throat Shifting Thrust Modulation

Correct Answer : Option (D) : Throat Shifting Thrust Modulation

Explanation : In Throat Shifting Thrust Modulation (TSTM), by shifting the throat of the nozzle, thrust is controlled. For modulation of thrust, the jet area is controlled using symmetric injection near the throat.

Which of the following thrust modulation techniques uses a normal shock to reduce total thrust?

Fluidic Thrust modulation

Shock Thrust Modulation

Throat Shifting Thrust Modulation

Scarfed Nozzle Thrust Modulation

Correct Answer : Option (B) : Shock Thrust Modulation

Explanation : Shock Thrust Modulation (STM) involves an axisymmetric injection of secondary flow into the diverging section of the supersonic nozzle and the creation of a normal shock by the interaction of oblique shocks. Across a normal shock, a supersonic flow becomes subsonic, thereby reducing exhaust velocity and total thrust. Fluidic Thrust Modulation is divided into STM and TSTM.