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INFLUENCE OF FILLING WATER ON air concentration

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Journal of Hydrodynamics 2011年第5期23卷 601-606页

作者： WU Jian-hua MA Fei DAI Hui-chao College of Water Conservancy and Hydropower Engineering Hohai University Nanjing 210098 China

The filling water inside the cavity below an aerator occurs for the flow of low Froude number or the small bottom slope of a spillway. The aerator may cease to protect against cavitation damages, and may even act as a generator of cavitation if it is fully filled by water. The experiments were conducted to investigate the influences of the geometric parameters, and then the filling water on the air concentration. The results show that the filling water, or the net cavity length, is closely related to the plunging jet length for a given aerator, and the air concentration at some section is proportional to the ratio Ln/Lj at a fixed Lj for different geometric parameters of aerators. Secondly, at the same ratio of Ln / Lj, the aerator with a larger height or a larger angle of ramp, or a larger bottom slope, would have a larger plunging jet length, and then a larger net cavity length based on the ratio of Ln / Lj. As a result, the large space of cavity, or the high air concentration of the flow could be obtained although the filling water increases also based on the fact that Lf = Lj - Ln. It is the space of the cavity that is the dominant factor to affect the air concentration of the flow.

关键词： aerator air concentration filling water jet length net cavity length

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

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Journal of Hydrodynamics 2015年第3期27卷 394-402页

作者：卫望汝邓军张法星田忠 State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University

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.

关键词： self-aeration air concentration open channel flows turbulence diffusion numerical model

HYDRAULIC RESEARCH OF AERATORS ON TUNNEL SPILLWAYS

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Journal of Hydrodynamics 2007年第3期19卷 330-334页

作者： RUAN Shi-ping WU Jian-hua WU Wei-wei XI Ru-ze College of Water Conservancy and Hydropower Engineering Hohai University Nanjing 210098 China Anhui Institute of Hydraulic Research Bengbu 233000 China

The selection of the configuration and size of an aerator was of importance for a tunnel spillway under the conditions of high speed flows. Experimental investigations were conducted on the effects of entrained air on the tunnel spillway in the Goupitan Project, based on the criterion of gravity similarity and the condition of aerated flow velocity of over 6 m/s, with physical models. The configurations of the aerators were presented of a larger bottom air concentration, to protect the tunnel spillway from cavitation as well as to see no water fills in the grooves.

关键词： cavitation aerator air concentration tunnel spillway the Goupitan Project

Analysis on Link Between the Macroscopic and Microscopic air–Water Properties in Self-Aerated Flows

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China Ocean Engineering 2018年第5期32卷 614-623页

作者： WEI Wang-ru XU Wei-lin DENG Jun TIAN Zhong ZHANG Fa-xing State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University

Self-aeration in high-speed free surface flows occurs commonly and is of interest to ocean engineering, hydraulic engineering, and environmental engineering. For two-phase air–water flows, macroscopic air–water flow properties develop gradually, accompanied by the change of microscopic air–water structures. In this article, representational experimental studies on macroscopic and microscopic characteristics of self-aerated open-channel flows are summarized and compared. The isolated effect of the flow Reynolds number and air quantity on the differences in air count rate and chord size are analyzed and discussed. The results show that the characterized flow depth y, affected by the turbulence transfer, is a specific criterion to distinguish the interior air–water structure development. Two distinct linear trends of self-aeration are found, depending on the y/yvariation with a breaking point at Cmean =0.50. The air count rate and size scale in self-aerated flows are affected by the air quantity of self-aerated flows, even with identical flow Reynolds numbers. Thus, a specific parameter is proposed to assess the air–water structures and a series of self-similarity relationships in self-aeration properties are obtained. The link between macroscopic and microscopic air–water properties results in significant scale effect on air–water structures in self-aerated flows.

关键词： self-aeration two-phase flows air concentration air bubble open channel

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

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Journal of Hydrodynamics 2015年第6期27卷 913-918页

作者：邓军张法星田忠许唯临刘斌卫望汝 State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University

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 = AC~ ＋ 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 concentra- tion, 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 disper- sing the jet flow in the plunge pool could reduce the influence of the jet flow on the scour.

关键词： jet flow air concentration velocity