Published on Jan 24, 2020
A gas turbine, also called a combustion turbine, is a rotary engine that extracts energy from a flow of combustion gas.
It has an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between.
Energy is added to the gas stream in the combustor, where air is mixed with fuel and ignited. Combustion increases the temperature, velocity and volume of the gas flow. This is directed through a nozzle over the turbine's blades, spinning the turbine and powering the compressor.
Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power aircraft, trains, ships, generators, and even tanks.
Theory of Operation
Gas turbines are described thermodynamically by the Brayton cycle, in which air is compressed isentropically, combustion occurs at constant pressure, and expansion over the turbine occurs isentropically back to the starting pressure.
In practice, friction and turbulence cause:
a) Non-isentropic compression - for a given overall pressure ratio, the compressor delivery temperature is higher than ideal.
b) Non-isentropic expansion - although the turbine temperature drop necessary to drive the compressor is unaffected, the associated pressure ratio is greater, which decreases the expansion available to provide useful work.
c) A pressure loss in the combustor - reduces the expansion available to provide useful work.
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