Experimental Study On The Influence Of Different Parameters Of Permeable Spur Dikes On The Flow Characteristics Of The Curved Section Of The Spillway Chute

As a traditional hydraulic structure,the spur dike has been used for a long time in river regulation.The permeable spur dike is an innovative form of the traditional spur dike,which integrates diversion and permeability effects.It has the advantages of improving water surface,reducing backwater in front of the dam and reducing water pressure on the dam body.At present,the permeable spur dike is mostly used in subcritical flow rivers.The spillway chute is mostly supercritical flow on steep slopes.When the spillway chute is arranged with a bend,the existing research on river with spur dikes can not be directly applied to the spillway engineering because of the complexity of the water flow in the bend.Therefore,through hydraulic model test,this study analyzes the influence of the flow characteristics of the spillway after the permeable spur dike with different parameters is arranged on the bend of the spillway.In this paper,a total of 75 hydraulic experiments were carried out for different lengths(3B/10,4B/10,B/2),heights(2B/25,3B/25,4B/25)and permeability(18.3%,26.4%,35.9%)of three spur dikes(decorating in the corners of 1/4,1/2,3/4;placement Angle is 60°,75°,75°respectively)under different single width flows(100m~2/h,160m~2/h,200m~2/h,240m~2/h,300m~2/h).The main research contents and conclutions are as follows:(1)The study on the improvement effect of parameters of permeable spur dike on water surface in bend.Based on the evaluation indexes such as the uniformity of water surface in bend and the maximum transverse gradient of water surface in bend,the influence rule of the length,height and permeability of the spur dike to the improvement of the water surface in bend after the permeable spur dike is arranged on the concave bank of the spillway is analyzed.With the increase of the length and height of the spur dike and the decrease of the permeability,the water surface uniformity of the bend increases and the maximum transverse water surface gradient decreases.According to the analysis of different unit discharge and based on the maximum transverse gradient of water surface and other auxiliary evaluation indexes,the recommended parameters of permeable spur dikes on the curved section of the spillway chute are as follows:The length of the spur dike is B/2,the height is 4B/25,and the permeability is 18.3%.(2)The study on the influence of parameters of permeable spur dike on the velocity in bend.Based on the analysis of 3d velocity data in bend,the distribution rules of longitudinal velocity,transverse velocity and transverse velocity along the section are obtained when the length,height and permeability of the spur dike change.For the longitudinal section close to the spur dike,the longitudinal velocity decreases first and then fluctuates in the layout area of the spur dike.The lowest point of the velocity appears at the first or second location of the spur dike.The increase of the length and height of the spur dike and the decrease of the permeability will lead to the decrease of the longitudinal velocity of each section.For the longitudinal section away from the spur dike,the longitudinal velocity increases along the path.Taking the layout area of the spur dike as the boundary,the longitudinal velocity of the section in front decreases with the increase of the length and height of the spur dike and the decrease of the permeability;The variation of the length and permeability of the spur dike has little effect on the longitudinal velocity of the section in back.However,the increase of the height of spur dike will lead to the increase of the longitudinal velocity.Because of the existence of circumfluence,there are surface flow area and bottom flow area.In the bottom flow area,the absolute value of transverse velocity increases with the increase of spur length and the decrease of permeability;In the surface flow area,the transverse velocity decreases with the increase of the length,the increase of the height and the decrease of the permeability.(3)The study on the influence of parameters of permeable spur dike on hydrodynamic pressure of curved floor.By analyzing the hydrodynamic pressure data of the bottom plate in bend,it is found that the influence rules of the length,height and permeability of the spur dike on the time-average pressure.After placing the spur dike,the time-average pressure increases,but the decreasing trend remains the same compared with no spur dike.With the increase of the length and height of the spur dike,the time-average pressure increases.The time-average pressure is not linearly related to the change of water permeability.When the water permeability is 26.4%,the time-average pressure of the bottom plate is the maximum.The variation of spur parameters has little influence on the fluctuating pressure.But the fluctuating pressure amplitude of the bottom plate of the curved channel behind the permeable gallows decreases compared with no spur dike.