Adjusting the Ejector Effect inside a Jet Engine Ground Test Facility - CFD Prediction and Validation

摘要

Recently a modern jet engine of the latest generation has been put into service at the engine test facility operated by the Institute of Jet Propulsion of the University of the German Federal Armed Forces Munich. But because of the fact, that the primary mass flow of the new MexJET engine is exceeding the mass flows of the already installed jet engines by more than twice it could not be accelerated beyond a certain power setting. At this operating point, too high velocities within the sound absorber cascades of the test facility have been observed. This physical value is directly related to the strength of the ejector effect which establishes due to the hot exhaust gas plume of the engine. As it has been shown in previous studies, the entrainment of secondary air could be controlled by reducing the effective diameter of the detuner. Thus the application of an orifice plate on the existing chute-detuner-assembly of the facility was considered. But too low secondary air can cause adverse flow phenomena such as hot gas recirculation. Therefore, extensive numerical simulations have been conducted to ensure safe engine operation up to maximum power setting. These included different simulations of the effectiveness of the orifice plate and validation of the CFD-model with an already operated engine. Based on the validated simulations, predictions of the test cell aerodynamics with the new test vehicle have been made with special emphasis on the limits of the facility and indications for adverse flow phenomena. It is shown that the measures were successful and the new engine can now be safely used over its entire power range.