| The flow of pollutant-containing fluids in environmental fluids can be regarded as gravity flow.The study of gravity flow in channels with slope breaks is of great significance for precise pollution control.In this project,the open channel flow with inflow of 4,6,and 8 L/s and the conservative and non-conservative gravity flow experiments with the equal excess density ratio of 0.01 were carried out in the 3°,6°,12°slope break channels.Supplemented by a comparative study of numerical simulation,the following main conclusions are drawn:(1)Three different density grid sensitivity tests were carried out on the low,medium and high slopes with an excess density ratio of 0.01 and an inflow of 4 L/s turbidity flow.It was concluded that the 280×40 density grid was sufficient to achieve reliable simulation results under the condition that the computational space could be saved.(2)Single slope 3°inflow single wide flow rate of 0.008 m~2/s,open channel flow experiment on the slope of the jet uniform flow,flow fast and thin;underwater gravity flow in slopes on the environment fluid strong entrainment,above the wall flow boundary layer at the bottom of the form of free shear layer thickness is about three times as much as the boundary layer,if the gravity flow as polluted water,underwater polluted water will be much lower than the open channel flow velocity of moving downstream,maintaining high pollutant concentration in bottom boundary layer.(3)Regardless of the different flow rates for open channel flow,whether at low or high slopes,the position where the water jump occurs through the slope break will continue to move in the forward direction as the flow increases,which is reflected in the low flow(4 L/s)and medium flow(6 L/s)at low slopes,the high flow rate(8 L/s)occurred at the position of the water jump from5 m to 5.6 m and then to 6 m,the water level rose to the downstream uniform flow0.0363 m,0.0467 m,0.0573 m;under high slope,the position of the water jump in the low,medium and high flows moved from 5.8 m to 6.3 m and then to 6.6 m,and the water level rose to the downstream uniform flow of 0.0386 m,0.0483 m,and 0.0532m.(4)The influence of different flows on the gravity flow on the slope is reflected in both the low slope and the high slope.Although the Fred number is greater than 1,it is not completely characteristic of open channel flow jet,and its sectional specific energy increases with the increase of flow thickness in the uniform flow section of the jet flow on the slope.(5)Fixed initial inflow volume of 4 L/s,open channel flows at different slopes are extremely narrow at the bottom of slope break,and violent tumbling hydraulic jumps occur within the range of less than 0.1 m.If pollutants are carried,they can be fully mixed by hydraulic jumps and evenly distributed in the downstream uniform flow section.However,conservative and non-conservative gravity flows show a gradual increase in flow thickness in a longer section of>1 m at the slope break.The bottom boundary layer is similar to open channel flow and maintains a high and relatively uniform concentration,but the upper free shear layer still maintains obvious density stratification and full mixing of anhydrous jump.(6)The specific energy of the gravity flow numerical simulation section under different slopes is proportional to the flow thickness on the slope,and it is not exactly the same as the open channel flow,and it has the characteristics of jet flow.At this stage,Fr>1.This law is shown in the specific energy curves of all gravity flow sections under different flow rates in this study.(7)Non-conservative and conservative gravity flows with different slopes and excess density ratio of single flow,such as 0.01,were all caused by deposition of particulate matter in the channel,resulting in short flow distance and small difference in head and density.The turbidity current is obviously subjected to the entrainment and deposition along the course of the brine flow,resulting in a lower concentration at the same section.Moreover,the higher the gradient is,the more obvious concentration at the bottom boundary layer corresponding to the maximum velocity on the slope and under the slope is caused by the entrainment and mixing of environmental fluids and the strong hydrojump dilution.Studies have shown that the hydraulic jump of gravity flow at slope breaks is much weaker than that of open channel flow,and does not affect the density stratification of gravity flow.It is not possible to judge whether it is a jet flow by using Fred number 1as the critical value of gravity flow.From the perspective of scientific and precise pollution control:the treatment of pollutant-containing underwater gravity flow can focus on the laminar flow at the bottom boundary. |
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