Abstract
The cavitation performance of an axial flow pump with inlet guide vanes for different flow rates is studied in this article. The effects of inlet guide vanes on pump hydraulic performance and cavitation are investigated, where the total vapor fraction of impeller zone ( Ftv) is calculated to predict the critical net positive suction head, which is compared with that predicted by efficiency criterion for different flow rates. The influences of the development of cavitation on internal flow in impeller zone are also investigated. The results obtained show that the cavitation performance of axial flow pump can be improved at off-design flow conditions by adjusting angles of inlet guide vanes to positive values at low flow rates and by regulating angles of inlet guide vanes to negative values at high flow rates. As the net positive suction head decreases, the vapor fraction first increases slowly and then increases greatly, clearly presenting cavitation process from inception to full development, which can be used to predict the required net positive suction head. When net positive suction head decreases to the value around required net positive suction head, the cavitation zone from tip of blade suction side close to leading edge and the cavitation zone from hub part of the blade suction side connect together. After the connection, the cavitation zones have great influence on the velocity flow, leading to the decrease in pump performance.
Highlights
The axial flow pump is widely applied in large hydraulic engineering, especially in the fields of drainage, irrigation, and water supply
When the angle of inlet guide vane (IGV) is 0°, the head slightly reduces in comparison with that without IGVs due to the additional hydraulic loss caused by the IGVs
The head increases for 210° of IGVs while it decreases for 10°, which is consistent with the previous result.[17]
Summary
The axial flow pump is widely applied in large hydraulic engineering, especially in the fields of drainage, irrigation, and water supply. Hosien and Selim[6] experimentally showed that the visual incipient of cavitation in the pump existed long before drop in pump head occurred, NPSHhead,3% was adopted to predict the NPSHr.[7,8,9] Avellan[10] and Zhang and Chen[11] presented the influences of cavitation development on fluid machinery efficiency by using NPSHeff.,1% to predict the critical cavitation. Christopher and Kumaraswamy[3] experimentally investigated the radial flow pump with three different leading edge (LE) profiles of the vane under cavitating case by measurement of noise and vibration. They revealed that the ways by monitoring noise signal and vibration signal were better to sense the NPSHr than ordinary methods. The internal flow in the pump at different stages of cavitation is analyzed
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