Propulsion-2
1) What are the differences between air-breathing and Rocket engine?
Air- breathing Engine Rocket engine
Altitude limitation No altitude limitation
Rate of climb decreases with altitude Rate of climb increases with altitude
Thrust decreases with altitude Thrust increases slightly with altitude
Engine ram drag increases with flight Engine has no ram drag; constant
speed. thrust with speed.
2) What are the factors to be considered in design of a turbine?
a) Shaft rotational speed
b) Gas flow rate
c) Inlet and outlet temperatures
d) Inlet and outlet pressures
e) Exhaust velocity
f) Power output required.
3) Differentiate between impulse stage and reaction stage turbines
Impulse stage Reaction stage
Expansion of the gas occurs only in the Expansion takes place both in stator
stator nozzles. and rotor.
The rotor blades act as directional Rotor converts the kinetic energy of
vanes to deflect the direction of the the gas into work and contributes a
flow. reaction force on the rotor blades.
The relative discharge velocity of the The relative discharge velocity of the
rotor is the same as the relative inlet rotor increases and the pressure
velocity because there is no net change decreases in the passages between rotor
in pressure between the rotor inlet and blades.
rotor exit
, 4) Define match point.
The match point is defined as the steady-state operating point for a gas turbine
when the compressor and turbine are balanced in rotor speed, power, and flow,
the operating points at the various power settings defining the operating line for
the given engine configuration.
5) Define total-to-total efficiency and state when it is appropriate to use this
efficiency.
Total-to-total efficiency is the ratio of the actual work done to the ideal work
T T h h
01 03 01 03
done corresponding to total inlet and total exit conditions.
tt T T '' h h''
01 03 01 03
For turbojet engines, where the exhaust energy is not a loss because the gases
are accelerated to a high velocity for propulsive thrust generation, total-to-total
efficiency is used.
6) Define degree of reaction for a turbomachine stage.
The degree of reaction of a turbomachine stage may be defined as the ratio of
the static or pressure head change occurring in the rotor to the total change across
the stage.
7) What are the materials suitable for use in turbine blades?
Steel , titanium alloys and nickel based alloys are mainly used, have varying
proportions of chromium and aluminium to improve the strength and
corrosion resistance at high temperatures.
8) What are the different methods of blade cooling?
1) Internal air cooling
a) Hollow blade, with or without inserts
b) Solid blade with radial holes, with or without inserts
2) External air cooling
a) Film cooling
b) Transpiration or effusion cooling
c) Root cooling
3) Internal Liquid cooling
a) Forced convection cooling
b) Free convection cooling
c) Evaporative cooling
4) External liquid cooling
a) Sweat cooling using porous blades
b) Spray cooling
1) What are the differences between air-breathing and Rocket engine?
Air- breathing Engine Rocket engine
Altitude limitation No altitude limitation
Rate of climb decreases with altitude Rate of climb increases with altitude
Thrust decreases with altitude Thrust increases slightly with altitude
Engine ram drag increases with flight Engine has no ram drag; constant
speed. thrust with speed.
2) What are the factors to be considered in design of a turbine?
a) Shaft rotational speed
b) Gas flow rate
c) Inlet and outlet temperatures
d) Inlet and outlet pressures
e) Exhaust velocity
f) Power output required.
3) Differentiate between impulse stage and reaction stage turbines
Impulse stage Reaction stage
Expansion of the gas occurs only in the Expansion takes place both in stator
stator nozzles. and rotor.
The rotor blades act as directional Rotor converts the kinetic energy of
vanes to deflect the direction of the the gas into work and contributes a
flow. reaction force on the rotor blades.
The relative discharge velocity of the The relative discharge velocity of the
rotor is the same as the relative inlet rotor increases and the pressure
velocity because there is no net change decreases in the passages between rotor
in pressure between the rotor inlet and blades.
rotor exit
, 4) Define match point.
The match point is defined as the steady-state operating point for a gas turbine
when the compressor and turbine are balanced in rotor speed, power, and flow,
the operating points at the various power settings defining the operating line for
the given engine configuration.
5) Define total-to-total efficiency and state when it is appropriate to use this
efficiency.
Total-to-total efficiency is the ratio of the actual work done to the ideal work
T T h h
01 03 01 03
done corresponding to total inlet and total exit conditions.
tt T T '' h h''
01 03 01 03
For turbojet engines, where the exhaust energy is not a loss because the gases
are accelerated to a high velocity for propulsive thrust generation, total-to-total
efficiency is used.
6) Define degree of reaction for a turbomachine stage.
The degree of reaction of a turbomachine stage may be defined as the ratio of
the static or pressure head change occurring in the rotor to the total change across
the stage.
7) What are the materials suitable for use in turbine blades?
Steel , titanium alloys and nickel based alloys are mainly used, have varying
proportions of chromium and aluminium to improve the strength and
corrosion resistance at high temperatures.
8) What are the different methods of blade cooling?
1) Internal air cooling
a) Hollow blade, with or without inserts
b) Solid blade with radial holes, with or without inserts
2) External air cooling
a) Film cooling
b) Transpiration or effusion cooling
c) Root cooling
3) Internal Liquid cooling
a) Forced convection cooling
b) Free convection cooling
c) Evaporative cooling
4) External liquid cooling
a) Sweat cooling using porous blades
b) Spray cooling
