基于图像灰度统计的调节阀空化分布特性研究

针对调节阀内复杂的空化流动现象，研究调节阀内的空化形态特征和分布特性。建立调节阀空化图像采集试验系统，采用高速相机对空化形态进行捕捉。由于空泡的生长、溃灭等动力学行为使空泡群的密度和数量的不同，捕获的图像上灰度值的变化与空泡的演变过程之间存在相关性。该文通过空化图像中灰度值的变化来识别空化区域，且为提高分析可靠度，引入三个特征量：相似系数R确定所需样本数量、灰度变化率λ来表征空泡的动力学行为变化、平均灰度值ψ表达空化长度。根据这三个特征量，我们准确获得了调节阀内空化产生的位置、分布区域以及形态的变化。调节阀流道内空化附着区域可分为空化形成区(IR)、发展区(DR)和溃灭区(CR)。背压是影响空化附着区域形态的一个重要因素。随着背压的增加，其对空化的抑制作用比较明显，空化形成区的终点也是溃灭区的起点，即空化在流道内的分布形式仅为空化形成、溃灭这两种分布形式。此外，随着背压的增加，空化强度减弱，空化长度亦减小。

Research on Cavitation Distribution Characteristics in Regulate Valve Based on Image Gray Statistics

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.