The effect of rotor tip clearance on stall inception in an axial compressor

The effect of tip clearance on the transient process of rotating stall evolution in the axial compressor stage with three stator-rotor gaps was investigated experimentally by the pressure traces on the casing wall. The measurement of the pressure field on the casing wall covering the rotor and the velocity distribution behind the rotor with a slanted hot wire were performed near the stall point to clarify the effect of the rotor tip clearance on the flow field. In the case of small clearance, the stall evolution depends on the stator-rotor gap. However, in the case of large clearance, there is little difference of the stall evolution among three gaps. From the measurement of the pressure and velocity field near the stall point, it seems that breakdown of tip leakage vortex occurs in the case of large clearance for three different gaps. It is supported from the axial velocity distribution at the rotor exit. From the pressure field traces just before the stall, we can find the distinctive flow phenomenon like rotating instability which was found previously by März, et al. The tip vortex plays a very important role for stall inception.