The purpose of GTU nozzle apparatus is to convert potential energy of escaping gases into kinetic energy.

Passing through the nozzle blades, the flow of exhaust gases acquires high circumferential forces and transfers them to the working stages.

On gas turbine models, where the temperature of exhaust gases from the CW is less than 800 °C, the nozzle blades have an uncooled design. At higher flue gas temperatures, air cooling is used. The air is extracted between compressor stages.

In order to allow for thermal expansion, the nozzle apparatus of the first stages is of a collapsible design, consisting of individual blade sections. Nozzle apparatuses of the following stages quite often have non-disassembled cast construction.

GTU nozzle apparatus has a higher temperature load than turbine working stages. Blades of the nozzle apparatus experience serious thermal stresses. Often, they are connected with non-uniformity of the temperature field. This often results in cracks and corrosion of the blades.

One of the most important requirements for maintaining the lifetime of the nozzle apparatus is a high level of flame and thermal resistance. Therefore, first stage blades are made of nickel or cobalt based alloys with high heat resistance.

Quite often, to increase resistance to high temperatures, the surface of the nozzle blades is coated with aluminum.