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In a gas turbine engine using pure reaction-type turbine blades, rotational forces are the direct result of…

  • A
    decreased gas velocity caused by convergent areas between turbine stators.
  • B
    increased gas velocity caused by divergent areas between turbine blades.
  • C
    aerodynamic action caused by divergent areas between turbine blades.
  • D
    aerodynamic action caused by convergent areas between turbine blades.

Refer to figure.

IMPULSE TURBINE
Nozzle guide vanes
(form convergent ducts – accelerate the gas)		Velocity increasesPressure decreases
Rotor BladesVelocity decreasesNo change in pressure
REACTION TURBINE
Nozzle guide vanes
Pressure remains constant
Rotor Blades
(form convergent ducts – accelerate the gas, creating reaction force which drives the turbine)		Velocity increasesBoth temperature and pressure decrease

According to Rolls Royce, in a reaction turbine, the nozzle guide vanes simply direct the gas onto the turbine blades. Therefore, there is no change in speed or pressure across them, only a change in direction.

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