One of the components of any gas turbine engine is the so-called output device. Its design is quite diverse. It can be a jet nozzle, a diffuser or a gas exhaust pipe, a thrust vector reversal or deflection device, various noise reduction devices or devices to reduce infrared visibility, mixing chambers for turbojet engines.

Each of these units has its own specific application area. It basically depends on the specific purpose of the engine, and, as a consequence, the aircraft. Modern output devices often combine different functions and can therefore be quite complex designs.

However, despite the variety, some of these functions can in a sense be called secondary (noise attenuation, for example, or visibility reduction). To the main ones for GTEs of direct reaction initially belonged the possibilities of forming the necessary parameters of the gas flow, coming out of the engine.

In this sense, the output devices can be divided into two groups. The first, by shaping the flow, makes its output pulse as large as possible and directs it in the desired direction. The second one does the opposite, i.e. turns the flow into a simple “exhaust”.

The first group are jet nozzles, the second group are diffusers and various kinds of exhaust pipes. If the name (and hence the purpose) of the engine contains the word “jet”, then the obligatory element of the output device will be a jet nozzle. In our case, these are different types of air-jet engines. Of course, in each of them, the nozzle has its own specific type and level of complexity of design.

It is worth noting separately that an important function of the nozzle is also to provide the possibility of stable joint operation of the elements of the GTE in the main modes. The size of the passage section of the nozzle affects the temperature of the flow, so it can be a factor in regulating the operation of the engine. Especially, if the nozzle is structurally able to change the area of the passage section.

A gas turbine engine, as a dynamic expansion machine, uses the disposable energy of the gas (which it has gained by heating and increasing pressure) to do work on the turbine. The gas expands in it, accelerating in the nozzles and rotating its impellers.

The resulting power is used to rotate the compressor and the so-called payload units. If actuating these units is the main function of the engine, as is the case, for example, in TvAD, then it is designed so that almost all the available energy of the gas (or most of it) is converted into mechanical work. Unless, of course, the engine is structurally perfect enough and is not engaged in “pumping” energetically charged gas into the atmosphere.

That’s why a helicopter gas turbine engine (turboshaft) usually has a diffuser gas outlet as an output device. The gas flow coming out of the turbine of such engine has already spent the vast majority of its disposable energy to rotate the main rotor, transmission and of course its own compressor.