Experimental study on spatiotemporal distribution characteristics of different cavitation stages based on the flow deviation method

Abstract

Cavitation may quickly damage the surfaces of the valve core and valve seat, causing noise, and vibration problems. Different cavitation stages will affect the regulating valve's flow characteristics to different degrees. Flow rate is one of the basic parameters in a hydraulic system, which is innovatively used to evaluate the cavitation flow. By analyzing the deviation ratio K between actual and theoretical flow rate, cavitation flows are divided into four stages, and the dynamic behavior in different stages is discussed using a high-speed camera and image processing technology. When K is zero, it is defined as the no-cavitation stage. A slight increase in K is the incipient cavitation stage, whose K is within 2%. A rapid decrease in K is the critical cavitation stage, while a significant increase in K is the severe cavitation stage. In the incipient cavitation stage, bubbles are adhered to the valve orifice forming attached cavities. In the critical cavitation stage, attached cavities develop along the throat wall, with some bubbles detaching to form free cavities. This process is accompanied by high-frequency shedding and collapses, with a dominant frequency of 4266 Hz. In the severe cavitation stage, larger attached cavities are located at the throat, whose front edge of cavitation will fracture into large-scale cavitation clouds. Furthermore, this study proposed the cavitation intensity to elucidate the spatial distribution and density of cavitation flow, the cavitation change rate to highlight the disturbances and nonuniformities caused by cavitation bubbles, and the cavitation coefficient to evaluate the severity of cavitation. Additionally, there is a strong correlation between the growth rate of cavitation length L and the growth rate of flow rate Q in the regulating valve. Both the growth rate of L and Q increase in the critical cavitation stage and decrease in the severe cavitation stage.