Modelling of an ejector for turbine aeroengines for application in performance synthesis tools

The operation of ejectors is well known, however no models are available in modern performance synthesis tools. For designing an engine the effect of an ejector on the operation of a turbine aero engine and vice versa is of interest. Therefore the development of a module for caclulation of ejector performance on a turbine aero engine with a convergent primary nozzle for application in a performance synthesis tool is described. The module is to allow a flexible representation of ejectors and an appropriate consideration of the operation in performance synthesis. Initially a simplified mathematical 1-D model of the ejector nozzle is presented. It is valid for a lossless, compressible flow of an air/combustion gas mixture. The model is able to solve the flow equations for complete mixing of primary and secondary flows in case of both subcritical and supercritical primary nozzle flow.

Integration of the model with the performance synthesis programme SAEPP (Sophisticated Aero-Engine Performance Program) as well as the iterative approach to solving the equations is described. Example calculations are performed at selected operating points of the micro gas turbine engine ILA001 and compared to the results without ejector. The subsequent discussion of the results shows that the model which thus far was lossless needs to be expanded to consider inlet, mixing and friction losses in ordner to correctly reflect the operating behaviour of an ejector.