| A Pratt and Whitney Canada PT6/T400 turboshaft engine has been instrumented specifically to determine if measurable compressor aerodynamic behaviour can provide a warning of impending stall or surge, especially in a small (<5 kg/s), service-exposed, axi-centrifugal compressor. The engine was instrumented with nine fast-response pressure transducers (monitored at 25 kHz) divided between the axial compressor first stage leading edge, the axial compressor exit, and the outlet of the centrifugal compressor diffuser. An automatic bleed valve was gradually disabled to cause compressor stall. The engine response to this gradual change corresponded to the predictions of a simple engine surge model. A signal processing technique was developed to monitor the strength of individual blade flows with a sampling rate only 3 times the blade-passing rate. This technique proved that aerodynamic changes could be successfully detected before surge. The new technique compared favourably to conventional fast Fourier transform and wavelet processing techniques. |
