Types of turbine blades

Introduction:-

                   The function of turbine is drive the compressor and accessories, and, in the case of the turboprop, the propeller, by extracting a portion of the pressure and kinetic energy from the high-temperature combustion gases.

In a typical Jet engine, about 75% of the power produced internally is used to drive the compressor.

Turbines:-

                      A portion of the kinetic energy of the expanding gases is extracted by the turbine section, and this energy is transformed into shaft horsepower which is used to drive the compressor and accessories. In turboprop and turbo shaft engines, additional turbine rotors are designed to extract all of the energy possible from the remaining gases to drive a power shaft.

A Turbine is a device which converts the heat energy of   steam into the kinetic energy & then to rotational energy

Types Of Turbine Blade:-

  ØImpulse

  ØReaction

  ØImpulse reaction

Impulse:-

•Impulse machine are those in which there is no change of static or pressure head of the fluid in the rotor.

•The rotor blades cause only energy transfer and there is no energy transformation. 

•Energy transformation takes placed in fixed blades only.

•Transfer of K.E to the rotor in an impulse turbine from high velocity fluid occurs only due to the impulsive actions of the fluid on the rotor.

Reaction:-

•Reaction machines are those, in which changes in static or pressure head occurs both in stator and rotor blade passages.

•The energy transformation occurs both in fixed as well as moving blade

•The rotor experience both energy transfer as well as energy transformation.

•The degree of reaction of turbomachine stage may be defined as ratio of static or pressure head occurring in rotor to the total change across the stages 

Impulse reaction:-

it is combination of both Impulse and Reaction

Difference Between Impulse & Reaction

Impulse

qDuring flow of steam   pressure drop only in the nozzle

qBlades are profile type

qPower developed is comparatively less

qBlades arne symmetrical

qNo.of stages required for given power is less qEfficiency is less qSteam velocity is more qIt is suitable for small power required qPressure remains constant while flowing over moving blades qManufacturing of blades is easy and hence inexpensive

Reaction qDuring flow of the steam pressure drop in the Fixed nozzle and Moving blades qBlades are aero foil type qPower developed Is more qBlades are not symmetrical qNo. of stages required for given power is more qEfficiency is more qSteam velocity is less qIt is suitable for medium or high power required qPressure reduced while flowing over moving blades qManufacturing of blades is difficult and hence costlier