The Thermodynamics of Exergy Losses and Thrust Production in Gas Turbine Engines

Abstract

The application of exergy analysis to aerospace systems requires proper analysis of the entropy generated during the wake equilibration process. Early studies of exergy analysis applied to aerospace systems focused on hypersonic vehicles and these studies revealed the significance of the wake contribution to the overall exergy loss. This current study focuses on exergy analysis at lower speeds and includes analysis of a ramjet and a single spool turbojet engine. Another focus of this study is on the transient exergy analysis of propulsion systems. With the use of an analytical model, this study reveals that, as in the case of hypersonic vehicles, the wake contribution to the overall entropy generation remains significant. Specifically, the rate of entropy generation in the wake region of a turbojet engine operating at cruse conditions is up to three times the rate of entropy generation inside the engine. In the next portion, a quasi-one-dimensional flow solver is used to model transient throttling maneuvers in a ramjet and a turbojet engine. This work indicates that for the fast throttling maneuvers in the case of the ramjet, the unsteady entropy generation terms are significant. However, due to the slow shaft dynamics, a quasi-steady exergy analysis (i.e. where the unsteady entropy generation terms are neglected) can accurately predict the performance of a gas turbine engine during transient maneuvers.