GASTURBINE EXHAUST SYSTEMS – Air – DGCA Question Bank For Politics

#1. The velocity of the gases in the exhaust unit is held to:

0.5 Mach to minimise turbulence.

0.75 Mach to optimise the pressure distribution.

0.85 Mach to maximise thrust.

Mach 1 to maximise acceleration.

#2. The exhaust cone:

Straightens the gas flow before it goes into the turbine assembly.

Prevents the hot gases flowing across the rear turbine face.

Increases the velocity of the gases.

Decreases the pressure of the gas.

#3. The propelling nozzle is designed to:

Increase the velocity and decrease the pressure of the gas stream.

Decrease the velocity and increase the pressure of the gas stream.

To increase the velocity and the pressure of the gas stream.

To decrease the velocity and the pressure of the gas stream.

#4. A nozzle is said to be “choked” when:

The gas flow through it is subsonic.

The gas flow through it reaches its sonic value.

The gas temperature rises.

The gas flow through it is supersonic.

#5. A choked nozzle:

Decreases thrust.

Gives additional pressure without the addition of heat.

Has no effect on thrust.

Implies that no further increase in velocity can be obtained without the increase of heat.

#6. The exhaust gasses pass to atmosphere via the propelling nozzle which:

Is a convergent duct, thus it increases the gas velocity.

Converts kinetic energy into pressure energy.

Is a divergent duct, thus it increases the gas velocity.

Is a divergent nozzle, thus it increases the gas pressure.

#7. The jet pipe is insulated from the airframe by:

Heat insulation materials.

A cooling air jacket.

A combination of cooling air and insulating material.

Semi-conducting geodetic structures.

#8. The noise from a high ratio by-pass engine:

Is created mainly in the exhaust section.

Is high in the exhaust section because of the high velocity gas flow.

Is predominantly from the fan and the turbine.

Is greater than that from a turbo-jet engine of comparable power output.

#9. The shape of the volume within the jet pipe casing immediately to the rear of the turbine:

Is convergent to accelerate the gases towards the propelling nozzle.

Is divergent to accelerate the gases away from the turbine blades.

Is convergent to increase the pressure of the gases in the jet pipes.

Is divergent to reduce the velocity of the gases leaving the turbine.

#10. The turbine rear support struts:

Prevent the hot gases flowing across the rear face of the rear turbine bearing.

Add swirl to the gases before they travel down the jet pipe.

Allow entry of the by-pass air into the exhaust system.

Straighten out any residual whirl in the gas stream.

#11. An exhaust nozzle is said to be choked when the velocity at the throat is:

Mach.5.

Below Mach 1.

At Mach 1.

Above Mach 1.

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