An adaptive logarithmic threshold framelet analysis of the partial surge initiated instability in a transonic axial flow compressor

Partial surge is a new type of instability inception in transonic axial flow compressors and occurs in the form of axisymmetric low-frequency disturbances localized in the hub region. The frequency of partial surge is about 12.5Hz at 88% of the design rotor speed, while the frequency of developed rotating stall cells in the final phase of the evolution is around 190Hz. As there are two different frequencies in the instability evolution of partial surge, it is difficult to well denoise the experimental data by general data processing methods that are focused on one single frequency. Considering the unique feature of the partial surge initiated instability, an adaptive logarithmic threshold framelet method has been built. By this method, the well-denoised results can be obtained. Based on the results, the instability evolution of partial surge is clearly shown. At the same time, several new findings about partial surge have been presented: (1) the propagating procedure of one partial surge disturbance: the amplitude of disturbance is increasing until one partial surge disturbance is developed; (2) the occurrence of rotating stall cells is related to the partial surge disturbance; (3) the propagating procedure of one rotating stall cell is presented; (4) the partial surge disturbance is well proved to be axisymmetric. Finally, the capability of this denoise method is also discussed.