PIV Experimental Study On Flow Structure Of Step-shaped Spur Dike

The step-shaped spur dike are widely used in waterway regulation engineering,but there are only a few studies on related hydraulic characteristics.The design and optimization of related schemes in waterway regulation still lack theoretical guidance.Therefore,it is of great theoretical and practical significance to study the flow structure of the step-shaped spur dike.Based on the PIV flume test results,this paper analyzes the difference of average velocity around the submerged step-shaped spur dike and the single-section spur dike,and discusses the influence law of the step-shaped spur dike scale and inflow conditions on the flow turbulence characteristics in the spur dike area.The following results are obtained:(1)On the inside of the step-shaped spur dike spur dike,the high-speed area with large velocity is located above the top of the spur dike and close to the upstream area.The longitudinal relative velocity u+ gradually increases along the flow and tends to be stable in the area far away from the spur dike downstream.(2)Along the channel width direction,the u+ of the step-shaped spur dike area gradually increases from the inside to the outside of spur dike,the u+ outside increases with the increase of water flow Q,and reaches the maximum value in the upstream area about 0.5?0.8 times of the length of the first-level spur dike.(3)With the same water flow and the same total water resistance area,compared with the single section spur dike,the inner side flow velocity of the step-shaped spur dike is smaller,which can avoid the inner flow erosion of the bank,while the outer flow velocity of the step-shaped spur dike is also relatively small,which may lead to insufficient silt erosion in flood season and affect navigation.The velocity near the head of the first-level spur dike is large,so it is necessary to protect the dam head in the waterway regulation project to avoid water damage caused by the erosion of dam head.(4)Along the direction of water depth,there is obvious stratified in the upstream of the step-shaped spur dike.On the inner side of the step-shaped spur dike and at the head of the first-level spur dike,the u+ near the bottom of the trough and near the surface of the water is small,in the middle area u+ fluctuates greatly and reaches the maximum value near the top of the dam.On the outside of the step-shaped spur dike,the u+ near trough bottom and near water surface area are small,in the middle area is more stable.(5)The relative longitudinal turbulence intensity Tux in the stepped spur dike area is greater than that the relative vertical turbulence intensity Tuy,and there are similar distribution law along the flow,both of which show a trend of gradually decreasing in the upstream and relatively stable in the downstream.(6)On the inside of the stepped spur dike and at the head of the first-level spur dike,the larger value area of relative Reynolds stress R+ is distributed in the upstream near the water surface,and the larger value area is distributed diverging from the spur dike crest of each section to the upstream.On the outside of the step-shaped spur dike,the larger value of R+ is distributed in the upstream area near the relative water depth y+=0.1 and the area near water surface,but the area near water surface is larger.(7)The relative value of turbulent kinetic energy E~+decreases gradually along the flow,and E~+decreases gradually from the inside to the outside of the spur dike along the groove width.The relative value of E~+of the upstream increases with the increase of the water flow Q,but the amplitude of the increase in the outside spur dike is smaller than that of the inside and the head of the first-level spur dike.(8)On the inside of the step-shaped spur dike and at the head of the first grade spur dike,the E~+ of the area near the bottom of the groove is small and relatively stable,from middle area E~+ begins to increase and has a large value near the top of the spur dike and fluctuates greatly in area near the water surface.On the outside of the step-shaped spur dike,the E~+ near trough bottom and near water surface area are larger,and on the middle area is more stable.