Slip phenomenon is known to strongly influence the performance of pump as turbine (PAT). It is of interest to investigate the influence of flow parameters on the slip factor and obtain the effective value of slip factor over the whole range of their working conditions.

In the present work, the slip phenomenon of PAT at different working condition was studied, slip factor was calculated in every point of the flow. Furthermore, the relative eddy within the impeller passage was evaluated and the hydraulic performance of PAT was analyzed.

The result shows that the slip factor decreases with the increasing flow rate, slip phenomenon induces additional hydraulic loss in impeller passage, it weakened in over-load region, as a consequence, hydraulic efficiency is relatively high. On the contrary, the slip phenomenon strengthened in part-load region, therefore, hydraulic efficiency of PAT is relatively low. It was observed that a relative eddy take place within the impeller passage, the eddy occurs near pressure side of blade at design-point condition, it motions to suction side at high discharge, and divides into two separated eddy at partial discharge condition. The relative eddy cause pressure fluctuate in PAT impeller, which affects the energy recovery of PAT.

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