New Discussion On Hydraulic Characteristics Of Stepped Spillway

Stepped spillways change the traditional smooth spillway slope to the steps,which have two functions of discharge flow and energy dissipation at the same time.Stepped spillway belongs to a new type of energy dissipation,which adopts the method of"decentralized"energy dissipation.The energy of flow consume step by step on the steps,So the stepped spillway has the high energy dissipation.Stepped spillway is widely used in practical hydraulic engineering.The hydraulic characteristics of stepped spillway have been research hot spot.Depending on model test stepped spillway,the paper discuss the energy dissipation,aeration properties and pressure distribution of step structure.Because of the conventional spillway slope has a certain roughness,it can block drainage water.Researching only hydraulic characteristics of steps spillway is not able to fully explain the influence of the steps to the drainage of water.So the author combine stepped spillway with smooth spillway,which contribute to compare and analyze the relative hydraulic parameters and further explore hydraulic characteristics of stepped spillway.The experimental results show the following conclusions:(1)When the connection ways between curved surface with initial step are not at the same time,the pressure distribution law of step is relatively consistent and the pressure size has major difference.(2)Step height has an impact on energy dissipation,and the influence has a close relationship with discharge per unit width.When the flow rate per unit width is small,step height has a weak effect on energy dissipation,however energy dissipation is more sensitive to the change of bench height in the big unit discharge.The finding are more clearly to explore the effect of bench height to energy dissipation,at the same time,it can provide the reference opinion for step spillway in practical application.(3)The article introduced the ratio of flow length and the average water depth,which is dimensionless number.And according to the analysis of three different structure step spillway of experimental data,the results show that the relative energy dissipation and the ratio of flow length and depth show a good linear rule.When the ratio of flow length and water depth is specific value,the relative energy dissipation ratio increase with the increase of discharge per unit width,step height and bottom slope.(4)When stepped spillways produce skimming flow,the velocity head of stepped spillways will be gradually increase and tend to be stable along the step length on non-uniform flow.The greater the flow rate per unit width,the longer the step length of the velocity head achieve stability,the stable value is higher.When the step height is higher or the spillway slope is gentle,the velocity head.is low.(5)This paper analyze velocity head along the change rule of the step spillway and traditional conventional spillway.It focus on the relationship of the relative velocity head and flow rate per unit width,step height and slope.Research shows that the relative velocity head of on non-uniform flow period is increasing along the performance for linear law when the water flow is skimming flow,and the correlation coefficient R~2 is between 0.9959~0.9988.The change of the relative velocity of water head has negatively correlated with flow rate per unit width,and has positively correlated with step height and slope of stepped spillway,particularly the influence of the slope.The spillway with a larger slope is more suitable for the use of the stepped structure.