UNSTEADY PRESSURE MEASUREMENTS OF SPIKE TYPE INCEPTION IN AXIAL COMPRESSOR: TIME FREQUENCY ANALYSIS AND AVERAGING PROCEDURE

Low flow rate regimes in aeronautical compressors are characterized by appearance of instable phenomena, as rotating stall, responsible for important stress in the machine structure and even associated to a real risk of failure. Enlarging the operating range to the highest compression ratio regimes is certainly a fundamental objective in the wider context of an enhancement of the performances and of a reduction of the environmental impact. Unsteady pressure investigations were carried out on a single stage low speed compressor during transition to fully developed rotating stall. The original data processing provided new lights on one of the most common mechanisms of stall onset, the so-called spike-type precursor. Wavelets Transform will be shown to be a promising tool for developing reliable techniques to detect precisely this kind of instability inception. In addition, it will be proposed an innovative phase-locked-average-based method able to underline casing pressure features proper to spike phenomenon, by isolating it from the background noise.