Study Of The Hydraulic Characteristics Of Right-angle Polyline Weir

With the continued promotion of ecological civilization,weirs have the functions of irrigation,water supply,flood safety and landscape needs,and are therefore widely used in ecological river management.However,due to the width of the river,traditional thin-walled weirs,utility weirs and broad-topped weirs,all of which cannot give full play to their overflow capacity,have resulted in increased upstream inundation and increased pressure on embankment flood control.In this paper,based on the experimental research results,the numerical simulation of the overflow capacity of nine right-angle polyline weirs is carried out by using the RNG k-ε turbulence model and Tur VOF free surface tracking method,in order to obtain the hydraulic characteristics and overflow capacity of the right-angle polyline weirs under free and submerged outflow conditions.On this basis,the distribution law of the overflow capacity of each component(front weir,side weir and back weir)of the right-angle polyline weir is further analyzed,and then the formula for calculating the flow rate of the front weir,side weir and back weir and the formula for calculating the submergence coefficient are obtained through the method of formula fitting,thus being able to provide a reliable theoretical basis for the design and engineering application of the right-angle polyline weir.The main results are as follows.(1)In terms of flow pattern,with increasing flow,the flow pattern of the right-angle polyline weir in the free flow condition includes: wall pressing flow,complete thin-plate weir flow,incomplete thin-plate weir flow and practical weir flow.In the case of submerged outflow,the flow patterns transition from submerged bottom flow to broken waves,surface waves,surface outflow and fully submerged outflow in sequence.(2)In terms of flow velocity,with increasing head at the top of the weir,the streamlines of the right-angle polyline weir in both free and submerged outflow situations change in a process that includes the front weir always remaining orthogonal to the body of the weir,the side weirs gradually moving from orthogonal to parallel,and the back weir moving from orthogonal to oblique and back to orthogonal.In terms of pressure,when the head at the top of the free outflow weir exceeds 100 mm,the negative pressure on the downstream side of the front,side and back weirs in turn appears and gradually increases.When the head at the top of the weir increases further to 150 mm,the negative pressure on the downstream side of the front,side and back weirs in turn disappears.In the case of submergence outflow,negative pressure appears at the top of the front,side and back weirs,and the maximum negative pressure is located near the corner B.However,as the degree of submergence increases,the negative pressure at the top of the front,side and back weirs gradually disappears.(3)In terms of overflow capacity,when the position of the side weir is kept the same and the length of the side weir is changed,the overall overflow capacity of the right-angle polyline weir tends to increase,but the increase gradually decreases.For the different weirs,the overflow capacity of the side weirs gradually increases,but the increase decreases;the overflow capacity of both the front and back weirs decreases,but the back weir decreases more.When the position of the side weir is changed(keep the length of the side weir the same and increase the length of the front weir),the overall overflow capacity of the right-angle polyline weir gradually increases and then decreases.The overflow capacity of the side weirs tends to increase and then decrease,while the overflow capacity of the front and back weirs is non-linearly and positively correlated with their own length.On this basis,the flow calculation formula for each component of the weir(front weir,side weir and back weir)were fitted separately for changes in relative head at the top of the weir.In the case of submerged outflow,with increasing submerged flow,the overall overflow capacity of the right-angle polyline weir tends to decrease.When the effects of the channel overflow width and the length of effective overflow edge of the right-angle polyline weir are considered separately,the correspondence between the submergence coefficient and the relative submergence degree of the right-angle polyline weir is obtained.Then,by means of fitting,the formula for calculating the overflow capacity of the right-angle polyline weir that can reflect the submergence characteristics was obtained.