Exercise 16. Practise out the dialogue.
T. The turbine section is one of three principal sections of any gas turbine engine. It is located after the combustion chamber. In the turbine section the kinetic energy of expanded gases is extracted and converted into useful rotational energy (корисна обертальна енергія/полезная вращательная энергия). This power is used to drive the compressor and accessories in a turbojet engine. And in a turboprop engine the power is used to drive the propeller as well. Look at Fig.II.4.1, please.
Fig.II.4.1 Typical arrangement of the turbine assembly
You see a typical arrangement of the turbine assembly. It consists of two parts: the turbine nozzle diaphragm (“сопловий апарат/ сопловой аппарат”) and the turbine rotor assembly (“робоче колесо турбіни/ рабочее колесо турбины”). The first component consists of hollow vanes welded between two concentric rings. The second part, that is the turbine-rotor assembly, consists of a turbine wheel or rotor and a set of stationary vanes. Where is the turbine section located?
S. The turbine section is located after the combustion section.
T. Quite right. What process takes place in the turbine section?
S. The kinetic energy of expanded gases is extracted and converted into useful rotational energy in the turbine section.
T. Thus, what is the function of the turbine assembly?
S. The function of the turbine assembly is to extract power from the jet stream for driving the compressor and accessories in turbojet engines and to drive the propeller as well in turboprop engines.
T. What does the turbine assembly consist of?
S. It consists of two parts: the turbine nozzle diaphragm and the turbine rotor assembly.
T. That’s correct. The function of the nozzle diaphragm is to accelerate and direct hot gases onto the buckets of the turbine wheel. The nozzle vanes are usually constructed of high temperature alloys.
And now look at Figure II.4.2., please.
Fig.II.4.2. Turbine rotor assembly
This picture shows the turbine rotor assembly. It is usually comprised of three main elements: a shaft, a turbine wheel or rotor and a set of stationary vanes. Turbine discs are constructed of corrosion-resistant high-temperature nickel alloys. Turbine buckets are usually forged from a heat-resistant nickel-chrome alloy. Turbine buckets are attached to the turbine wheel rims by the fir-tree attachment (хвостовик типу “ялинка“ / хвостовик типа “елочка”). What does the nozzle diaphragm serve for?