Download ME6604- GAS DYNAMICS AND JET PROPULSION Multiple Choice

ME6604- GAS DYNAMICS AND JET PROPULSION
Multiple Choice Questions:
1. The efficiency of a jet engine is higher at
1. low speeds
2. high speeds
3. low altitudes
4. high altitudes
2. In a centrifugal compressor, an increase in speed at a given pressure ratio causes
1. decrease in flow
2. increase in flow
3. increase in flow and decrease in efficiency
4. increase in efficiency
3. The stagnation pressure rise in a centrifugal compressor takes place
1. in the diffuser and impeller
2. in the diffuser only
3. in the inlet guide vanes only
4. in the impeller only
4. In a jet propulsion
1. the propulsive matter is ejected from within the propelled body
2. the propulsive matter is caused to flow around the propelled body
3. its functioning does not depend upon presence of air
4. none of the above
5. Intercooling in multi-stage compressors is done
1. to enable compression in two stages
2. to cool the air at delivery
3. to cool the air during compression
4. to minimise the work of compression
6. In the aircraft propellers
1. the propulsive matter is ejected from within the propelled body
2. its functioning does not depend upon the presence of air
3. the propulsive matter is caused to flow around the propelled body
4. none of the above
7. The ratio of workdone per cycle to the stroke volume of the compressor is known as
1. compressor capacity
2. compression ratio
3. compressor efficiency
4. mean effective pressure
8. The maximum delivery pressure in a rotary air compressor is
1. 30 bar
2. 40 bar
3. 10 bar
4. 20 bar
9. The compressed air may be used
1. for operating pneumatic drills
2. in gas turbine plants
3. in starting and supercharging of I.C. engines
4. all of the above
10. The volume of air delivered by the compressor is called
1) free air delivery
2) compressor capacity 3) swept volume
4) none of these
11. Which of the following statement is wrong?
1) The ratio of the volume of free air delivery per stroke to the swept volume of the piston is called
volumetric efficiency.
2) The minimum work required for a two stage reciprocating air compressor is double the work
required for each stage.
3) In a two stage reciprocating air compressor with complete intercooling, maximum work is saved.
4) none of the above
12. The maximum temperature in a gas turbine is
1) 700°C
2) 200°C
3) 500°C
4) 100°C
13. Rotary compressors are used for delivering
1) small quantities of air at low pressures
2) large quantities of air at high pressures
3) small quantities of air at high pressures
4) large quantities of air at low pressures
14. In axial flow compressor, exit flow angle deviation from the blade angle is a function of
1) blade camber and space-chord ratio
2) space-chord ratio
3) blade camber and incidence angle
4) blade camber
15. The volumetric efficiency for reciprocating air compressors is about
1) 40 to 60%
2) 60 to 70%
3) 10 to 40%
4) 70 to 90%
16. The type of rotary compressor used in gas turbines, is of
1) centrifugal type 2) axial flow type
3) none of these
4) radial flow type
17. Only rocket engines can be propelled to space because
1) they can generate very high thrust
2) these engines can work on several fuels
3) they have high propulsion efficiency
4) they are not air-breathing engines
18. Which of the following statement is correct as regard to centrifugal compressors?
1) The impeller rotates at high speeds.
2) The flow of air is parallel to the axis of the compressor.
3) The static pressure of air in the impeller increases in order to provide centripetal force on the air.
4) The maximum efficiency is higher than multi-stage axial flow compressors.
19. In a centrifugal compressor, the highest Mach number leading to shock wave in the fluid flow
occurs at
1) diffuser outlet radius
2) impeller outlet radius
3) diffuser inlet radius
4) impeller inlet radius
20. Gas turbine as compared to steam turbine
1) has less efficiency
2) has compressor and combustion chamber
3) all of these
4) requires less space for installation
21. The type of rotary compressor used in aeroplanes, is of
1) centrifugal type
2) axial flow type
3) radial flow type
4) none of these
22. The axial flow compressor is preferred in air-craft gas turbines because of
1) high pressure rise
2) low frontal area
3) higher thrust
4) none of these
23. A turbo-prop is preferred to turbo-jet because
1) it can fly at high elevations
2) it has high propulsive efficiency at high speeds
3) it can fly at super sonic speeds
4) it has high power for take off
24. A rocket engine uses __________ for the combustion of its fuel.
1) its own oxygen
2) compressed atmospheric air
3) surrounding air
4) none of these
25. A jet engine has
1) propeller in front
2) propeller at back
3) propeller on the top
4) no propeller
26. Which of the following statement is correct relating to rocket engines ?
1) The combustion chamber in a rocket engine is directly analogous to the reservoir of a super sonic
wind tunnel
2) The stagnation conditions exist at the combustion chamber
3) all of the above
4) The exit velocities of exhaust gases are much higher than those in jet engine
27. The thrust of a jet propulsion power unit can be increased by
1) burning fuel after gas turbine
2) all of these
3) injecting water into the compressor
4) injecting ammonia into the combustion chamber
28. In a jet engine, the air-fuel ratio is
1) 50:1
2) 30:1
3) 40:1
4) 60:1
29.A roket works with maximum overall efficiency when air-craft velocity is……………….. the jet velocity.
1) equal to
2) one-half
3) double
30.Rayleigh line flow is a flow in constant area duct
1) with friction but without heat transfer
2)without friction but with heat transfer
3) with both friction and heat transfer
4)without either friction or heat transfer
31. For oblique shock, the downstream Mach number
1) is always more than unity
2) is always less than unity
3) may be less or more than unity
4) can never be unity
32.Fanno line flow is a flow in constant area duct
1) with friction and heat transfer
2) with friction and heat transfer and accompanied by work
3) with friction but in the absence heat transfer or work
4) without friction but accompanied by heat transfer and work
33. The prime parameter causing change of state in a fanno flow is
1) heat transfer
2) Area change
3) Friction
4) buoyancy
34. In a normal shock in a gas, the
1) upstream flow is supersonic
2) upstream flow is subsonic
3) down stream flow is sonic
4) both downstream flow and upstream flow are supersonic
35. which one of the following is the correct sequence of the position of the given components in a
Turboprop?
1) Propeller, compressor, turbine, burner
2) Compressor, Propeller, burner, turbine
3) Propeller, compressor, burner, turbine
4) Compressor, Propeller, turbine, burner
36. For a jet propulsion unit, ideally the ratio of compressor work and turbine work is
1)2
2) 1
3) not related to each other
4) unpredictable
37.A normal shock
1) causes a disruption and reversal of flow pattern
2) may occur only in a diverging passage
3) is more serve than an oblique shock
4) moves with a velocity equal to the sonic velocity
38.The fluid property that remains unchanged across a normal shock wave is
1) stagnation enthalpy 2) stagnation pressure 3) static pressure 4) mass density
39.The turbine of the turbo-prop engine as compared to that of turbo-jet engine is
1) similar
2) smaller
3) bigger
4) unpredictable
40. which one of the following is proper for a normal shock wave?
1) Reversible
2) Irreversible
3) Isentropic
4) Occurs in a converging tube