Effects of air bubble quantity on the reduction of cavitation erosion

Abstract

Dam observations indicated that low-air concentration can avoid cavitation erosion. In the present study, a device with micron-scale orifice diameters was designed to introduce air bubbles in water, to study the effects of the reduction of cavitation erosion in an ultrasonic environment. The experimental results showed that low-air concentration imposes prominent effects on the development of cavitation erosion and can significantly reduce the effect of cavitation on the structural damage. If the air concentration and bubble quantity reach certain values, the erosion reduction effects do not change as the air conditions are altered. Based on the analysis of the average erosion reduction efficiency of a single-air bubble, aeration and erosion protection for the wall surface can be achieved. Moreover, a discharge tunnel with high-head and high-speed water flow is analyzed. With a high velocity and low-air concentration flow in the open channel, no cavitation erosion on the tunnel structure was observed. Combined with the present experimental results, this shows that the effect of the aeration erosion reduction can be evaluated and analyzed if the air bubble quantity meets the erosion reduction requirement. Consequently, the effect of aeration can be recognized effectively by number of air bubbles, and can promote the design and analysis of the aeration erosion reduction in hydraulic engineering.