文丘里管不同空化阶段空化不稳定特性的试验研究

Experimental Investigation of the Instability of Cavitation in Veturi Tube under Different Cavitation Stage

采用高速摄像技术研究文丘里管在空化数分别为0.76、0.51、0.26的三种不同状态下的空化流动现象,比较不同工况下空化云脱落的具体方式,利用图像处理工具分析空化云面积的变化规律,研究空化云脱落和各测压点压力变化之间的关联关系。结果表明,空化云从文丘里管喉管起始段近壁面处生成以后,逐渐向下游发展,在不同空化阶段呈周期性的以不同的方式脱落。随着空化数的减小,空化云脱落方式由单一的上下同时脱落向单边脱落转变,而单边脱落又以下边脱落为主。当空化非常剧烈时,在扩散管内出现多段不连续的团状空化云。另外,空化云脱落与扩散管内3个不同位置的压力脉动有很强的关联性,而与喉部内压力脉动关联不大。空化云脱落的主频与扩散管内压力脉动主频几乎完全对应,且随着空化程度的加剧而递减,对应主频分别为275.9 Hz、176.8 Hz、12 Hz。

A high-speed camera is used to observe the cavitation flow under different stages corresponding to the cavitation number of 0.76,0.51 and 0.26.The shedding ways of cavity cloud under different conditions are compared.The area variations of cavity cloud are analysed by image processing tools.The relations between shedding laws of cavity cloud and change laws of pressure in different position are studied.The experimental results are conducted.Cavity cloud produced from internal face in throat of venture tube develops downstream,and periodically sheds in different ways under different cavitation stages.As cavitation number reduces orderly,the shedding ways of cavity cloud convert to unilateral shedding from bilateral shedding.Particularly,unilateral shedding mostly consist of nether shedding.When cavitation is very severe,multistage discontinuous cavity cloud appear in the diffuser.Additionally,the shedding of cavity cloud has a strong association with the pressure fluctuation in three different position in diffuser,but it has little association with the pressure fluctuation in throat.The dominant shedding frequency nearly corresponds to the dominant frequency of pressure fluctuation.And both of the dominant frequency orderly decrease as cavitation get violent,respectively corresponding to 275.9 Hz,176.8 Hz,12 Hz.