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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

High-speed photographic observation of collapse of two cavitation bubbles

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Science China(Technological Sciences) 2016年第11期59卷 1707-1716页

作者： LUO Jing XU WeiLin LI Rui state key laboratory of hydraulics mountain river engineering Sichuan University

Cavitation as a hydrodynamic phenomenon exists widely in water conservancy, shipbuilding, chemical and many other *** cavitation bubble dynamic studies mainly focused on single cavitation bubbles and their interaction with the wall. This paper studies the interaction between two cavitation bubbles under conditions with or without a wall. The results show that if the inception of two cavitation bubbles is not synchronized, the cavitation bubble of early inception collapse backwards the cavitation bubble of later inception; if the inception of two cavitation bubbles is synchronized, the two bubbles collapse towards each other; if a wall exists nearby, no matter whether the line connecting the centers of the two cavitation bubbles is vertical or parallel to the wall, the two cavitation bubbles collapse towards each other and then gradually merge, and the merged collapse body quickly moves to the wall. It is suggested that, as the number of cavitation bubbles increases, the cavitation erosion effect is not simply increased proportionally. Instead, mutual inhibitory effect may be demonstrated.

关键词： cavitation bubble high-speed photography shock wave micro-jet

Heat transfer at ice-water interface under conditions of low flow velocities

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Journal of Hydrodynamics 2016年第4期28卷 603-609页

作者：李楠脱友才邓云李嘉梁瑞峰安瑞冬 state key laboratory of hydraulics and mountain river engineering Sichuan University

The heat transfer at the ice-water interface is closely related to the hydrodynamic and physical properties of the water *** affects the ice cover thickness and the water temperature underlying the ice *** paper studies the heat transfer from the water to the ice *** on the flume data,a linear relationship between the ice-water heat transfer coefficient and the flow velocity beneath the ice cover is established and the calculated dimensionless ice-water heat transfer coefficient is 1.1×*** empirical relationship can be applied to estimate the ice-water heat transfer of reservoirs,lakes and other freshwater bodies when the flow velocity under the ice cover is in the range of 0.024 m/s-0.110 m/s.

关键词： reservoirs beneath hydrodynamic dimensionless freshwater turbulence turbulent deviation affects thick

Cavitation bubbles collapse characteristics behind a convex body

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Journal of Hydrodynamics 2013年第6期25卷 886-894页

作者：李瑶许唯临张亚磊张敬威陈春祺阿蓉 state key laboratory of hydraulics and mountain river engineering Sichuan University

Cavitation bubbles behind a convex body were experimentally studied by a high speed camera and a hydrophone synchronously. The experiments were conducted in a circulating water tunnel with five various contraction ratios： β = 0.497, β= 0.6, β= 0.697, β= 0.751, and β= 0.799. The distributions of the cavitation bubble collapse positions behind the five different convex bodies were obtained by combining the images taken by the high speed camera. According to the collapse positions, it was found that no cavitation bubble was collapsed in the region near the wall until the ratio of the water head loss over the convex body height was larger than 20, which can be used to predict if the cavitation damage would occur in the tunnel with orifice energy dissipaters.

关键词： convex body cavitation bubble collapse high speed camera cavitation noise

Dominant factor and incremental depth formula for self-aerated flow in open channel

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Journal of Hydrodynamics 2018年第4期30卷 651-656页

作者：白瑞迪张法星王韦刘善均 state key laboratory of hydraulics and mountain river engineering Sichuan University

The presence of air in open channel flows will increase the bulk of the flow, and is of great importance in the design of spillway and chute sidewalls. hydraulics in the developed region is investigated in this paper systematically by a series of model and prototype investigations. It is verified that the velocity in the aeration region is the dominant factor. For the flow with an identical velocity but a different flow depth, the air concentration distributions are nearly the same. From the theory based on the formation of drops on the surface by the turbulent liquid jets and the vortex deformation, a formula to calculate the incremental depth is obtained by best correlating the model and prototype investigations. The formula is reasonable with less mean error than those obtained by other methods, which could recommended for the use in engineering designs.

关键词： Aerated flow aeration incremental depth unaerated black water aeration flow depth

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

A laterally averaged two-dimensional simulation of unsteady supersaturated total dissolved gas in deep reservoir

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Journal of Hydrodynamics 2013年第3期25卷 396-403页

作者：冯镜洁李然杨慧霞李嘉 state key laboratory of hydraulics and mountain river engineering Sichuan University

Elevated levels of the Total Dissolved Gas （TDG） may be reached downstream of dams, leading to increased incidences of gas bubble diseases in fish. The supersaturated TDG dissipates and transports more slowly in reservoirs than in natural rivers because of the greater depth and the lower turbulence, which endangers the fish more seriously. With consideration of the topographical cha- racteristics of a deep reservoir, a laterally averaged two-dimensional unsteady TDG model for deep reservoir is proposed. The dissi- pation process of the TDG inside the waterbody and the mass transfer through the flee surface are separately modeled with different functions in the model. Hydrodynamics equations are solved coupling with those of water temperature and density. The TDG con- centration is calculated based on the density current field. A good agreement is found in the simulation of the Dachaoshan Reservoir between the simulation results and the field data of the hydrodynamics parameters and the TDG distribution in the vertical direction and their unsteady evolution with time. The hydrodynamics parameters, the temperature and the TDG concentration are analyzed based on the simulation results. This study demonstrates that the model can be used to predict the evolutions of hydrodynamics para- meters, the temperature and the TDG distribution in a deep reservoir with unsteady inflow and outflow. The results can be used in the study of the mitigation measures of the supersaturated TDG.

关键词： total dissolved gas supersaturation unsteady flow reservoir

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

Experimental and field study on dissipation coefficient of supersaturated total dissolved gas

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Journal of Central South University 2014年第5期21卷 1995-2003页

作者：冯镜洁李然马倩王乐乐 state key laboratory of hydraulics and mountain river engineering(Sichuan University)

The elevated supersaturation of total dissolved gas （TDG） downstream of a high-dam spill has deleterious effects on fish in a large range. A one-dimensional （l-D） longitudinal model is optimal for the prediction of supersaturated TDG dissipation over a long distance. The key issue of the model is to determine the dissipation coefficient accurately. In agreement with field observations and experiment data, dimensional analysis and regression were performed to propose a formula for estimating the dissipation coefficient of supersaturated TDG in various rivers and reservoirs, and it involves the effects of the turbulence intensity, the hydro-pressure and the solid-liquid interface. The friction velocity, water depth, hydraulic radius and Froude number are independent variables in the formula which are easy to determine in practical applications. The 1-D longitudinal model is implemented to calculate the dissipation of TDG in a reach of the Jinsha river. Good agreement is found between the calculated results and field data for both the dissipation coefficient and the dissipation process.

关键词： total dissolved gas dissipation coefficient longitudinal model hydrodynamics