Experimental Analysis On The Characteristics Of Unidirectional Diffusion Flow After Water Gate

Diffusion flow is a common phenomenon in water conservancy projects.It often exists in the vicinity of the river,water pump station,water inlet,outlet and water station and the horizontal arrangement of combined buildings.This phenomenon has an innegligible influence on the flow field around it.The adverse flow patterns,such as slanting flow,vortex and circulation,will cause a great security threat to the downstream energy dissipator and the channel and river bed.If the diffusion angle is too large,the flow separation will occur around the downstream buildings,and the unsteady vortex motion will be produced in the separation area.The safety of things has a serious adverse effect.With the change of flow,gate opening,downstream water depth and other factors,the influence degree is not the same,so it is very important to study the downstream flow field of the building under this diffusion.This paper mainly studies the discharge capacity of the gate and the one-way diffusion flow characteristics behind the gate.Two schemes of full section overflow scheme and narrow channel over current are designed by physical model test,and 57 operating conditions.Potassium Permanganate solution is used as tracer to observe the flow state,and the velocity is measured by ADV.Through the arrangement and analysis of the test results,the flow field in the downstream is compared with the flow field under the condition of diffusion and non diffusion.The mechanism of the diffusion and the main factors affecting the diffusion are analyzed.The laws of the diffusion after the sluice are summarized,as follows:(1)The study of the hydraulic characteristics of the two schemes,it is found that the water level curve of the narrow section overflow scheme is basically the same as that of the full section overflow scheme.Under the same single wide flow rate,when the relative opening of the gate is the same,the relationship between the single width flow of the two schemes and the water depth before the sluice is basically the same.The overflow coefficient of the full section scheme is calculated to be between 0.6~0.8 and the overflow coefficient of the narrow section scheme is between 0.4~0.6.(2)The diffusive flow behind the gate is divided into two regions: nearing the diffusion plate and along the main direction.The disadvantageous flow behind the sluice mainly includes the oblique flow of the opposite side wall near the main side,the axis vortex in the vicinity of the diffusion plate and the horizontal circulation downstream.The slanting water flow on the side wall guide wall has formed scour and erosion,and the vertical vortex is liable to cause serious scour to the river bed.The transverse circulation is the main force causing sediment movement,which has a serious influence on the erosion and siltation of the river bed.(3)the velocity and vorticity of the diffuser plate are small and easy to form siltation;the flow velocity and vorticity of the main line are larger,and it is easy to form erosion.