Experimental and unsteady numerical research of a high-specific-speed pump for part-load cavitation instability

Hong Li,Nicholas Engen Pedersen,Zhenhua Shen,Christian Brix Jacobsen

doi:10.1177/1687814019828932

Hong Li, Nicholas Engen Pedersen + Show 2 more

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https://doi.org/10.1177/1687814019828932

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Abstract

Net positive suction head peak is a well-known cavitation instability phenomenon in high-specific-speed pumps. Both non-cavitating performance and cavitating performance of a high-specific-speed pump were investigated by experiments and numerical simulations. According to the cavitating performance results, net positive suction head peak is found at 80% of nominal flow. The head curves of non-cavitating performance also have saddle-type instabilities near 70%–80% of nominal flow. Water vapor volume fraction distributions show that cavitation region at net positive suction head peak flow only covers 3% of the blade length when head drops 6%. It proves that net positive suction head peak is not caused by huge amounts of cavitation bubbles, which indicates that net positive suction head peak does not represent excessive cavitation. The velocity vector and pressure distribution plots reveal that net positive suction head peak is related to recirculation near the trailing edge. With inlet pressure decreasing, the flow pattern is sensitive to the cavitation bubbles, and recirculation region from the pressure side to the suction side becomes larger and larger.

Highlights

Many of the pump cavitation investigations report that cavitation instability exists in some of the centrifugal and mixed-flow pumps.[1]
Net positive suction head (NPSH) peak at part load is one of the instability phenomena, the peak value indicates an enlarged danger of cavitation attack, and it requires high inlet pressure to prevent the cavitation in the pump engineering world
Schiavello described that instability was linked to the suction recirculation, and both net positive suction head at 1% head drop (NPSH1%) and net positive suction head at 3% head drop (NPSH3%) peaks happened near the performance instability flow rate.[3]

Summary

Introduction

Many of the pump cavitation investigations report that cavitation instability exists in some of the centrifugal and mixed-flow pumps.[1]. Minami et al found a peak value at part load in cavitation inception curve by NPSH experiment with a visual pump model. They did not report any of the NPSH peak on their models.[4,5] When coming to the 21th century, Friedrichs and Kosyna did lots of part-load cavitation instability research work for different specific-speed (nq) impellers.

Results

Conclusion