Dynamic Response of Turbofan Engine in the Event of Shaft Failure: Fan and Compressor Operating Points and Turbine Overspeed Analysis

Abstract A physics-based component-level model has been developed to investigate the dynamic response of a turbofan engine in the event of shaft failure. The mechanism of the dynamic response of a turbofan engine without any fan or compressor surge is first discussed and analysed. The results show that the shaft failure essentially has a great impact on the functional integrity of the turbofan engine, causing the operating points of the fan and compressors to deviate from the steady-state lines and the speed of the turbine which loses load to increase rapidly. Meanwhile, the fan or compressor, which is affected by the shaft failure but is still connected to the turbine via the shaft, attempts to achieve a new power balance with the turbine. After shaft failure, the rapid reduction in core mass flow causes the operating point of the fan or compressor to quickly traverse the surge boundary, so the dynamic response of the turbofan engine after any fan or compressor surge is also investigated and analysed. The results show that during the surge, where severe blockage occurs, together with the fan or compressor losing drive, exacerbates the degradation of the turbofan engine performance, causing the total mass flow and pressure ratio to first rapidly decrease and then increase. In summary, the surge of any fan or compressor and its triggering of combustor flameout, which affect the average angular acceleration of the turbine by affecting the power, are actually beneficial to prevent the turbine from overspeed or even disc burst after shaft failure.