Experimental Study On The Law Of Gas Motion In Self-aerated Water Flow Without Lid And With Lid

As our country pays more and more attention to the sustainable development and utilization of water resources,the construction of water conservancy and hydropower projects has achieved unprecedented development.In large-scale water conservancy projects,high-head buildings will have many hydraulic problems during operation.For example,cavitation damage of buildings will affect the safe operation of hydraulic buildings,and excessive water turbulence will cause intense mixing of water and air,Causing the problem of supersaturation of dissolved gas in downstream water bodies and destroying the ecological environment.Therefore,it is particularly important to study the laws of gas movement in self-aerated water streams.This experiment will study the gas motion law of self-aerated water flow under uncovered and covered conditions,and compare and analyze the gas motion under covered and uncovered conditions.Research indicates:Self-aerated water flow area division: According to the self-aerated water flow aerated concentration distribution characteristics,the longitudinal aerated water flow is divided into three areas: no aerated area,aerated development area and aerated balance area;From bottom to top along the direction of water depth,aeration is divided into: no aeration zone,bubble suspension zone and water point jump zone.The distribution characteristics of water flow velocity and water depth in each subarea: the velocity of the non-aerated zone and the aerated development zone increases from the bottom to the water surface,and the surface velocity is the fastest;the maximum velocity of the aerated balance zone is at the upper part of the middle of the water flow,and the minimum is at the water flow At the bottom,there is a small difference between the flow velocity of the middle water flow and the upper water flow.The increase rate of the flow velocity attenuates along the way,and the flow velocity distribution is a process of increasing along the depth of the water and then gradually decreasing.The self-aerated water flow attenuates along the water depth,and its attenuation speed is: aerated development zone>aerated balance zone>aerated zone.The aeration concentration distribution and gas migration and diffusion movement characteristics of each zone: change with the change of flow velocity and water depth.The increase of the flow velocity will enhance the longitudinal migration strength of the gas,and the increase of the water depth will reduce the vertical diffusion strength of the gas,thereby affecting the longitudinal,vertical and lateral aeration concentration distribution of the self-aerated water flow and the length of the aerated structure zone.At the same time,an increase in aeration concentration will increase the water depth and decrease the flow velocity.The aeration concentration distribution and gas movement law under uncovered and covered conditions: Compared with the water flow under uncovered conditions,the aeration concentration and water depth decrease after the channel is covered,and the water flow velocity increases.The existence of the cap has two main influences on the law of gas movement.On the one hand,the gas pressure in the channel is lower than the atmospheric pressure,and a large amount of air migrates downstream with the increase of the turbulence of the water flow,which causes the pressure difference between the inlet of the channel and the air pressure in the channel to increase.On the other hand,the water point that jumps out of the cover falls back after inelastic collision,which affects the distribution of aeration concentration.This experimental study can provide references for building anti-cavitation damage and water ecology and water environmental protection.