Exergy Analysis for the Performance Evaluation of Different Setups of the Secondary Air System of Aircraft Gas Turbines

Abstract

Secondary Air System related losses in aircraft gas turbines cannot be directly assessed and quantified as possible for other sub-systems of the engine. If a particular setup is to be evaluated and compared to other, competing designs, it is required to have a distinct understanding of the loss mechanisms and the way these losses appear in the cycle. The relevant loss phenomena are therefore discussed in detail and are quantified with regard to the respective specific entropy increase. The exergy method is found to be the method of choice, since it holds some important advantages compared to other loss accounting methods like gas horsepower or thrust work potential. An exergy analysis is carried out for a high TET, two shaft engine of the medium thrust range. A comparison of setups with different compressor offtake positions is performed. It is found that the contribution of Air System related losses to overall engine efficiency deficits is significant, but may be reduced by careful design.