Book 2 - Turbines

Question 1

NGV’s (_______ ______ _____) are placed in front of each turbine ____ and are used to direct and ___________ gas flow on to the turbine _______

Answer 1

NGV’s (NOZZLE GUIDE VANES) are placed in front of each turbine ____ and are used to direct and ACCELERATE gas flow on to the turbine BLADES

Question 2

what are the two types of turbine?

Answer 2

• impulse

- reaction

Question 3

what type of turbine is used in gas turbine engines?

Answer 3

impulse/reaction

Question 4

the blade shape of a pure impulse turbine is…

Answer 4

cup shaped

Question 5

impulse/reaction turbine blades are of ________ shape with a _______ cup shape at the forward part of the blade. the remainder of the blade is aerofoil in section where an aerodynamic reaction is created similar to that of a wing

Answer 5

impulse/reaction turbine blades are of AEROFOIL shape with a PARTIAL cup shape at the forward part of the blade. the remainder of the blade is aerofoil in section where an aerodynamic reaction is created similar to that of a wing

Question 6

_________ passages are formed between blades in the turbine which __________ the air, causing further rotation and even greater rotational _______

Answer 6

CONVERGENT passages are formed between blades in the turbine which ACCELERATES the air, causing further rotation and even greater rotational FORCE

Question 7

the primary factor that limits the amount of power a gas turbine can produce is the maximum TIT (_______ _____ _________). where more than one turbine stage is used, ITT (_________/__________ ______ __________) may also be considered

the _______ the inlet temperature, the greater the efficiency. this is limited by ___________ available

Answer 7

the primary factor that limits the amount of power a gas turbine can produce is the maximum TIT (TURBINE INLET TEMPERATURE). where more than one turbine stage is used, ITT (INTERSTAGE/INTERMEDIATE TURBINE TEMPERATURE) may also be considered

the HIGHER the inlet temperature, the greater the efficiency. this is limited by MATERIALS available

Question 8

_____-staged turbines enable increased RPM without increasing ___________ loads. up to _____ stages are normally used

Answer 8

MULTI-staged turbines enable increased RPM without increasing CENTRIFUGAL loads. up to THREE stages are normally used

Question 9

the turbine assemblies are identified by the __________ they drive, e.g. the LP turbine will drive the LP __________

Answer 9

the turbine assemblies are identified by the COMPONENTS they drive, e.g. the LP turbine will drive the LP COMPRESSOR

Question 10

in a power (____) turbine, the only mechanical link is the output ______, which drives the propeller or rotor head

Answer 10

in a power (FREE) turbine, the only mechanical link is the output SHAFT, which drives the propeller or rotor head

Question 11

the losses which prevent a turbine from being 100% efficient are due to a number of reasons. 3.% loss would be suffered due to aerodynamic losses in turbine and 4.% lost due to aerodynamic losses in NGV’s, gas leakage over the _____ blades and _______ system losses. _% is lost in total, resulting in a 92% efficiency.

Answer 11

the losses which prevent a turbine from being 100% efficient are due to a number of reasons. 3.5% loss would be suffered due to aerodynamic losses in turbine and 4.5% lost due to aerodynamic losses in NGV’s, gas leakage over the ROTOR blades and EXHAUST system losses. 8% is lost in total, resulting in a 92% efficiency.

Question 12

the flow characteristics of the turbine must be carefully _______ with those of the __________ to obtain maximum _________ and performance from the engine

Answer 12

the flow characteristics of the turbine must be carefully MATCHED with those of the COMPRESSOR to obtain maximum EFFICIENCY and performance from the engine

Question 13

the turbine disc is manufactured from heat-resistant steel, usually _________ alloys

Answer 13

the turbine disc is manufactured from heat-resistant steel, usually NIMONIC alloys

Question 14

an increase in turbine temperature has been achieved through blade _______. a percentage of _____ flow is passed through holes formed in the blades which reduces the blade _______ temperature. this means TIT can be increased without affecting the material

Answer 14

an increase in turbine temperature has been achieved through blade COOLING. a percentage of MASS flow is passed through holes formed in the blades which reduces the blade SURFACE temperature. this means TIT can be increased without affecting the material

Question 15

the majority of gas turbine engines use the ___ tree fixing. accurate machining is required to ensure that loading is shared by all serrations. the blade is ____ in the serrations when the turbine is stationary and is ________ in the root by centrifugal loading

Answer 15

the majority of gas turbine engines use the FIR tree fixing. accurate machining is required to ensure that loading is shared by all serrations. the blade is FREE in the serrations when the turbine is stationary and is STIFFENED in the root by centrifugal loading

Question 16

every time a blade is used, it is always _______ when it cools than when it was at the same temperature before use. this growth is called _____. the initial creep is called _______ creep; most of its life, where growth occurs very gradually is called __________ creep; the much accelerated growth prior to failure is _________ creep

Answer 16

every time a blade is used, it is always _______ when it cools than when it was at the same temperature before use. this growth is called _____. the initial creep is called _______ creep; most of its life, where growth occurs very gradually is called __________ creep; the much accelerated growth prior to failure is _________ creep

Question 17

modern _______ crystal blades are very strong and highly resistant to ______

Answer 17

modern SINGLE crystal blades are very strong and highly resistant to CREEP

Question 18

further to single crystal blades, coating the blades with a ________ coating allows higher TIT and reduces _____

Answer 18

further to single crystal blades, coating the blades with a CERAMIC coating allows higher TIT and reduces CREEP