Wavelet Analysis of Rotor-Tip Disturbances in an Axial-Flow Compressor

Dynamic pressure signals taken from a low-speed axial compressor are analyzed with a wavelet transform. Several practical issues of continuous wavelet transforms, within the context of rotor-tip flow analysis, are discussed. The discrete form of continuous wavelet transform is presented with a graphical derivation that uniquely explains a complicated mathematical process with a readable graphical language without losing much mathematical strictness. With this wavelet tool, the data from a low-speed, three-stage axial compressor are analyzed. In these data, the wavelet analysis is able to pinpoint the exact time when spikes were initiated, as early as hundreds of rotor re volutions prior to stall, and track them thereafter. It is found that the emergence of the spikes is strongly related to two structural asymmetries of this compressor, one in the rotating frame and the other in the stationary frame. The spike development is not continuous. The ability to track the prestall process in both time and space, as demonstrated in this paper, makes wavelet analysis an effective tool for investigating the complicated instability phenomena of axial compressors.