Unsteady Transition Characteristics of Rotating Stall in a Single-Stage Transonic Axial Compressor
The unsteady transition characteristics of rotating stall have been studied experimentally in a single-stage transonic axial compressor. Three tested conditions in the near design and below design speed range, at tip relative Mach numbers from 1.26 to 1.0, were performed. The characteristics of rotating stall were studied by its dynamic behavior on the scale of compressor circumference and also by the flow field details in the blade passage. The dynamic behavior was analyzed by the technique of successive frequency spectrum and the flow field details were studied through internal transient pressure patterns in the blade passage plotted by the dynamic pressure data measured on the compressor shroud. It has been shown that intermittent pre-stall perturbations are evident for all the tested speeds and distinct by the different time and length scale of their existence. These are also interpreted by the difference of pressure loading and shock structure visualized in the pressure plots in the blade passage during stall inception. The pre-stall perturbations, with rather scattered frequency spectra, grow into fully developed stall abruptly. Nevertheless, the frequency spectrum of rotating stall falls into constant fraction of the frequency of compressor rotation for all the tested conditions. The increasing trend of the amplitude of pressure oscillation of rotating stall while gathering at its frequency spectrum could be detected in the stage of stall inception. Based on these two observations, there is a possibility of warning the stall precursors even for the high speed transonic compressor like the one tested in this paper.