3 - Gas Turbine Configurations and Heat Cycles

Abstract

This chapter explains the concept of gas turbine configuration. When defining heat cycles, it is necessary to specify the reference engine stations or the positions used for the pressure and temperature measurements that detail the heat cycle. It is also a must to define the flow of that cycle. This information helps define the gas turbine's configuration and efficiency. Ambient air passes from free stream to the flight intake leading edge. The air accelerates from the free stream. The compressor then increases both the pressure and temperature of the gas. Depending on the complexity, the turbojet compressor pressure ratio ranges from 4:1 up to 25:1. The compressor exit diffuser passes the air to the combustor. Here, fuel is injected and burned to raise exit gas temperature. The hot, high-pressure gas then is expanded through the turbine, where work is extracted to produce shaft power; both temperature and pressure are reduced. The turbine nozzle guide vanes and blades are cooled. This utilizes relatively cool air from the compression system. On leaving the turbine, the gas still is at a pressure typically at least twice that of ambient. This results from the higher inlet temperature to the turbine. Ultimately, in the downstream of the turbine, the gas diffuses in the jet pipe. This short duct transforms the flow path from annular to a full circle at entry to the propelling nozzle.