Stability assessment of an airflow distorted military engine’s FAN

Abstract

Military aircraft are often subjected to severe flight maneuvers with high Angles of Attack (AOA) and Angles of Sideslip (AOSS). These flight attitudes induce non-uniformity in flow conditions to their gas turbine engines which may include distortion of inlet total pressure and total temperature at the Aerodynamic Interface Plane (AIP). Operation of the downstream engine's compression system may suffer reduced aerodynamic performance and stall margin, and increased blade stress levels. The present study presents a methodology of evaluating the effect of inlet flow distortion on the engine's fan stability. The flow distortion examined was induced to the AIP by means of changing the aircraft's flight attitude. The study is based on the steady state flow results from 27 different flight scenarios that have been simulated in CFD. As a baseline model geometry an airframe inspired by the General Dynamics/LMAERO F-16 aircraft was chosen, which has been exposed to subsonic incoming airflow with varying direction resembling thus different aircraft flight attitudes. The results are focused on the total pressure distribution on the engine's (AIP) face and how this is manifested at the operation of the fan. Based on the results, it was concluded that the distorted conditions cause a shift of the surge line on the fan map, with the amount of shift to be directly related to the severity of these distorted conditions. The most severe flight attitude in terms of total pressure distortion, among the tested ones, caused about 7% surge margin depletion comparing to the undistorted value.