Influence of ATF Dynamics and Controls on Jet Engine Performance

Current and future requirements in the verification and validation of the performance of modern aircraft engines lead to continuously increasing requirements on the transient performance capability and flexibility of Altitude Test Facilities (ATF). These requirements have been investigated via numerical simulations of a medium size turbofan and a modern core engine. The simulations using the turbofan engine, document a significant influence of the boundary conditions supplied by the ATF on the dynamic behaviour of bypass engines. Variations in engine acceleration times and compressor stability have been identified. This leads to stability requirements for entry conditions at Fan face and ambient conditions at the nozzle exit. The especially demanding operability tests with core engines, challenge ATF systems due to the additional need to simulate the behaviour of low pressure components. It turns out that the interaction between test vehicle and ATF, in both cases, requires special attention and great care in the design of the ATF control system. Therefore a closed loop simulation model including, ATF, ATF controls system, test vehicle and vehicle control has been developed in order to assess and evaluate the integrated ATF - test vehicle behaviour in advance of the test. The integration of the test vehicle and vehicle control into the modular simulation tool is described. The standardized interface allows integrating different vehicle types without a lot of effort. The application of the simulation in a core engine ATF test is described as an example. The observed vehicle - ATF interaction with and without control is discussed.