Cavitation is regarded as a considerable factor causing performance deterioration of pumps under off-design conditions, especially at overload conditions. To investigate the unsteady cavitation evolution around the tongue of a pump volute, and its influence on the flow field within passages of the impeller, numerical calculations and several hydraulic tests were performed on a typical centrifugal pump with a shrouded impeller. Emphasis was laid on the cavitation evolution and blade-loading distribution at flow rates above the optimal value. Results indicated that vapor is likely to first emerge from the tongue of the volute rather than at the leading edge of the blades at overload conditions. In contrast to the designed condition, the flow distribution in each passage is obviously different. The flow rate of the passage reaches a maximum just past the location of the tongue, while the minimum flow rate value is projected to appear at the passage upstream. The cavitation at the tongue squeezes the flow area at the outlet of the corresponding flow passage of the tongue, thereby causing a huge growth in the flow rate at the impeller outlet.

中文翻译：

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高于最佳条件的流量下离心泵蜗壳内的空化流

空化被认为是导致泵在非设计条件下，特别是在过载条件下性能下降的重要因素。为了研究泵蜗壳的舌头周围的非定常空化演变及其对叶轮通道内流场的影响，对典型的带罩叶轮的离心泵进行了数值计算和几次水力试验。重点放在高于最佳值的流率下的气蚀演变和叶片载荷分布。结果表明，在过载条件下，蒸汽很可能首先从蜗壳的舌头而不是叶片的前缘逸出。与设计条件相比，每个通道中的流量分布明显不同。通道的流速刚好超过舌头的位置，达到最大值，而最小流速值则预计会出现在通道的上游。舌部上的气穴现象挤压了舌部相应流道出口处的流通面积，从而导致叶轮出口处的流量大幅增长。