Abstract: In view of the complex cavitation flow phenomenon in the regulate valve, the cavitation morphology and distribution characteristics in the regulate valve are studied experimentally. An experimental system of capturing cavitation bubbles in regulate valve is established, and the cavitation flow is recorded by a high-speed camera. Because of the growth and collapse of cavitation bubbles, the density and number of cavitation bubbles are different, and there is a significant correlation between the gray value of the captured images and the evolution of cavitation bubbles. In this paper, the change of gray value in cavitation image is used to identify the cavitation region. Then three parameters are introduced to improve the reliability of the analysis:similarity coefficient R representing the number of samples needed, change rate of gray level λ representing the dynamic behavior of cavitation bubbles, and the average gray-level value ψ representing the cavitation length. According to these three parameters, the position, size distribution and shape properties of cavitation flows in the regulate valve are accurately obtained. The cavitation attachment area in the flow passage of the regulate valve could be divided into the cavitation inception region(IR), development region(DR) and collapse region(CR). Furthermore, back pressure is one of the important factors that affects the shape of cavitation attachment region. The increasing back pressure has an obvious inhibitory effect of cavitation bubbles, and the end of cavitation formation region is also the starting point of the collapse region, that is to say, the distribution of cavitation in the channel is only cavitation inception and collapse. With the increase of the back pressure, the cavitation intensity and the cavitation length decrease.

Key words: regulate valve, gray statistics, cavitation distribution, cavitation development