The main function of turbine in an aero-engine is to drive the compressor. It also converts the energy from the hot gas flow coming from the combustion chamber into mechanical rotatory power that is imparted on the shaft; this is called torque. Additionally, the turbine must drive the accessories. In a turboprop engine, on the other hand, the primary function of turbine is to drive the propellers. In the case of a shaft engine, its main task is to drive the rotor blades of a helicopter.
Basically, turbine operation is not different from that of the compressor. While a compressor adds energy to the air flow passing through it by converting mechanical energy into pressure energy, a turbine conversely absorbs energy from the gas flow to convert it into mechanical shaft power or torque, which in turn drives the compressor. The great turbine power, which may reach values of 50,000 horsepower, is accomplished by extracting part, or sometimes all, of the energy contained in the hot gases, which are the product of combustion.
The amount of energy absorbs by the turbine is only as much as is required for driving the compressor and accessories (fuel pump, oil pump, electric generator). In aero-engines, the axial-type turbine is exclusively used because of the higher mass flow rate it makes possible. A radial-type turbine is, in fact, also possible. However, it is not a practical alternative. The design of the axial-type turbine can be single, or multi-stage.
Below, image shows the compressor, the shaft, and the turbine.
Simple schematic drawing showing the compressor, combustion chamber, the turbine and the shaft.
