Faxing Zhang

INTERACTION OF A CAVITATION BUBBLE AND AN AIR BUBBLE WITH A RIGID BOUNDARY

The motion of a spark-induced cavitation bubble and an air bubble near a rigid boundary is experimentally studied by using high-speed photography. Several dimensionless parameters are used to describe the geometrical configuration of the bubble-bubble-boundary interaction. The bubble-bubble interaction can be considered in two different conditions. The cavitation bubble will collapse towards the air bubble if the air bubble is relatively small, and away from the air bubble if the air bubble is relatively large. The two zones are identified in the bubble-boundary interaction, and they are the danger zone and the safety zone. The relative position, the bubble-boundary distance and the bubble-bubble distance play important roles in the bubble-bubble-boundary interaction, which can be considered in several conditions according to the responses of the bubbles. Air jets are found to penetrate into the cavitation bubbles. The cavitation bubble and the air bubble (air jet) move in their own way without mixing. The motion of a cavitation bubble may be influenced by an air bubble and/or a rigid boundary. The influence of the air bubble and the influence of the boundary may be combined, like some thing of a vector.

Experimental Investigation of Air–Water Flow Properties of Offset Aerators

AbstractAlthough chute aerators have been investigated experimentally by many researchers, only a few studies have been conducted on the comprehensive air–water flow properties of the lower jet dow...

A numerical model for air concentration distribution in self-aerated open channel flows

The self-aeration in open channel flows, called white waters, is a phenomenon seen in spillways and steep chutes. The air distribution in the flow is always an important and fundamental issue. The present study develops a numerical model to predict the air concentration distribution in self-aerated open channel flows, by taking the air-water flow as consisting of a low flow region and an upper flow region. On the interface between the two regions, the air concentration is 0.5. In the low flow region where air concentration is lower than 0.5, air bubbles diffuse in the water flow by turbulent transport fluctuations, and in the upper region where air concentration is higher than 0.5, water droplets and free surface roughness diffuse in the air. The air concentration distributions obtained from the diffusion model are in good agreement with measured data both in the uniform equilibrium region and in the self-aerated developing region. It is demonstrated that the numerical model provides a reasonable description of the self-aeration region in open channel flows.

Laboratory model study of the effect of aeration on axial velocity attenuation of turbulent jet flows in plunge pool

In the laboratory model experiment, the velocities of the jet flow along the axis are measured, using the CQY-Z8a velocity-meter. The velocity attenuations of the jet flow along the axis under different conditions are studied. The effects of the aeration concentration, the initial jet velocity at the entry and the thickness of the jet flow on the velocity attenuation of the jet flow are analyzed. It is seen that the velocity attenuation of the jet flow along the axis sees a regular variation. It is demonstrated by the test results that under the experimental conditions, the velocity along the axis decreases linearly. The higher the air concentration is, the faster the velocity will be decayed. The absolute value of the slope K increases with the rise of the air concentration. The relationship can be defined as K = ACa + Kb. The coefficient A is 0.03 under the experimental conditions. With the low air concentration of the jet flow, the thinner the jet flow is, the faster the velocity will be decayed. With the increase of the air concentration, the influence of the thickness of the jet flow on the velocity attenuation is reduced. When the air concentration is increased to a certain value, the thickness of the jet flow may not have any influence on the velocity attenuation. The initial jet velocity itself at the entry has no influence on the variation of the velocity attenuation as the curves of the velocity attenuation at different velocities at the entry are practically parallel, even coinciding one with another. Therefore, improving the air concentration of the jet flow and dispersing the jet flow in the plunge pool could reduce the influence of the jet flow on the scour.