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Because the gas turbine performance varies significantly from one design to the other, the procedure to determine the performance of the engine for a specified operating point is to use the manufacturer’s performance maps.
Today, these maps are usually embedded in software programs that allow the calculation of performance parameters of the engine. In general, these maps can be used to determine the engine full load output at a given ambient temperature, and a given power turbine speed. They also show the fuel flow at any load, as well as exhaust flow and temperature. Additional maps allow correction for inlet and exhaust losses as well as for the site elevation. For diagnostic purposes, the maps also allow to determine the expected compressor discharge pressure, control temperature (typically power turbine inlet temperature or exhaust temperature) and gas generator speed at any operating point.
This article contains excerpts from the paper, "Gas turbine performance", presented at the 2016 Turbomachinery Symposium by Klaus Brun of Southwest Research Institute and Rainer Kurz of Solar Turbines.
Discrepancies between the expected and the actual values may be indicative of engine problems. In order to fully understand the information displayed on engine performance maps, we want to determine what the reason is for an engine to behave the way it does. It should be noted that, particularly in the field, the measurement of power output, heat rate, exhaust flow and exhaust temperature are usually rather difficult. Understanding the operating principles of the engine is therefore a useful tool of interpreting data.