Cavitation instability in pump part-load condition is an ongoing subject of research due to erosion and noise. For some high specific speed (nq) pumps, NPSH_(3%)-peak at part-load represents one of the cavitation instabilities. This paper describes the recent investigations and results on performance and cavitation instabilities of a high nq pump. An n_q 99 impeller that shows a NPSH_(3%)-peak at 70% of nominal flow rate is investigated by using numerical calculations and experiments. Both experimental and numerical results show that the head curves also have instability phenomenon near 70-80% of nominal flow rate. By analyzing simulation results, part-load recirculation near the shroud is found both under non-cavitating and cavitating conditions. With the pressure decreasing, the recirculation zone become larger and cavitation bubbles influence the flow pattern near the trailing edge at the suction side.
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