Compressibility is an important feature of gas in unsteady process. This paper presents a numerical model to describe the compressibility effect of engine transient performance by solving the equations of mass flow, energy and momentum conservation.

In order to compare the difference of compressibility effect on the engine transient performance, the volume of each component was considered individually and the transient performance of a turbojet engine and a turbofan engine were simulated respectively.

The turbojet engine transient performance results showed that the component’s compressibility effect had a little effect on the engine transient performance, and the model proposed in this paper was able to capture more details than the traditional actuator-volume model. It also indicated that the influence of component’s compressibility on the engine performance depends on the relative position of the component and turbine nozzle. The volume of components such as compressors and burners before the turbine nozzle, slowed down the engine transient response; and the components such as turbines and afterburners after the turbine nozzle, influenced the turbine expansion ratio, thereby affected the engine transient performance.

The results of a turbofan engine indicated that the volume effect of the LP components hardly influenced the core. The volume effects of HP component on the core engine were similar with the turbojet.

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