超小型叶栅空化流场试验研究

Experiment Research of Cavitating Flow over Mini Cascade

采用弦长为14 mm的超小型Clark-Y叶栅,进行了多种空化数下的空化试验以探讨超小尺度下的空化机理和空化尺度效应。通过试验结果的分析,发现随着空化数降低,超小型叶栅的空化发展可分为空化初生、片状空化、云状空化、超空化几个阶段。通过与超小型翼型空化流场比较,发现由于受翼型间相互作用的影响,栅中翼型的空穴形态在各个空化阶段均表现为薄且狭长,空化发展相对滞后。

The mini pump having the characteristic dimension of 1 ~ 50 mm, has been becoming promising fluid machinery with the growing application in aerospace, new energy and agricultural machinery area for its small size. The cavitating flows over cascade having the chord length of 14mm have been investigated in a cavitation tunnel at different cavitation numbers to study the mechanism and scale effects of cavitation at miniature dimension. Based on the analysis of experimental results, it is shown that the cavitation in miniature flow passage can experience several states such as cavitation inception, sheet cavitation, cloud cavitation and super cavitation with the decrease of cavitation number. For the mini cascade cavitating flow, the cavity characteristics are different from that of single mini hydrofoil because of the interaction among the flows in neighboring flow channels. The mass transfer between liquid and gas phase caused by cavitation for mini cascade is less intense than that for single mini hydrofoil. Thus, there is no large scale cavity shedding in cloud cavitation period in mini cascade. Also, the cavity shape of mini cascade appears thinner and longer at different cavitation states and cavitation development is also hysteresis.