The Effect of Flight Speed and Altitude on Windmilling Restart Operation of Turbofan Engine System

The unpredictable flame-out may occur due to various factors such as weather conditions and bird strikes. After flame-out, the engine should undergo a challenging and risky restart process to restore thrust. Simulation model is an economy and repeatable tool to conclude the effects of flight speed and altitude on this extreme process. In this paper, a thermodynamic model is constructed in a modular scheme, with respect to the analysis and prediction of the restart performance in different flight environments. The equations containing the temperature polynomial and the corrected torque are added to the fan and compressor model to ensure convergence of cycle analysis in the low rotation speed region. The similarity theory and backbone mapping approach are integrated to generate the full mode characteristics required for fan and compressor models. The shaft acceleration control loop, which has been used in many advanced aero-engine is applied to the fuel controller to tightly control the shaft acceleration. Based on developed model, the effects of flight speed and altitude on the start-up time and performance parameters are studied. The results indicate that higher altitude and Mach number shorten the start-up time. Besides, the results show that the turbine operates under more extreme conditions when the restart operation is conducted at high altitudes.