The purpose of a turbine is to convert the kinetic energy of the flow of hot gases generated by burning fuel in the combustion chamber, into mechanical rotational energy.
Most of the turbine’s rotational energy (about 55-60%) is used to drive the compressor, in order to compress and supply air to the combustion chamber.
The turbine consists of several stages of working (rotating) and nozzle (fixed in the casing) blades.
The hot gas flow leaving the combustion chamber has a large kinetic energy. Passing through the stages of the nozzle vanes, the flow acquires potential energy and transfers it to the working stages. The working vanes are fixed in disks, which in turn are mounted on the rotor.
The nozzle apparatus of the first stages, installed in the housing, quite often has a collapsible design and consists of separate sections of blades. This is necessary to allow for thermal expansion.
To prevent gas leaks and loss of efficiency, banded seals are used in the design.
In most modern designs, one or more turbine stages are cooled to improve reliability and efficiency. Cooling air with certain parameters is taken between the compressor stages.
In multi-shaft GTU layouts, the design also provides for a free turbine. In such arrangement, the power turbine is used to drive the compressor, and the free turbine is used to drive the electric generator. Nevertheless, at any arrangement, the electric generator drive is carried out through a gearbox, in order to give the required rotation speed.
