Experimental and numerical investigations on the unsteady casing flow field in a one-and-half stage low speed axial compressor have been carried out. By using fast response pressure transducers instrumented on the rotor casing, the pressure time series were acquired at different operation points from throttle wide open to near-stall operation point. The pseudo-spatial pressure contours, phase-locked averaged and root-mean-square pressure contours and power spectrums of unsteady pressure signal have been achieved. The CFD simulations were conducted to help understanding the features of tip leakage vortex.

The rotating instability has been detected throughout an operation range from small flow rate point to near stall point. The frequency characteristic of rotating instability according flow rate was discussed. Based on the pattern of RIF varying with flow rate, the developing process of rotating instability according to flow rate could be divided into two stages, referred as early-developing stage and fully-developed stage. By analyzing the correlation between rotating instability and casing flow field, it was discovered that the origination and development of rotating instability was closely related to the fluctuation induced by tip leakage vortex.

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