Study On The Hydraulic Characteristics Of Stilling Basin With Drop Sill

Basic energy dissipation styles are compared at first. Although underflow energy dissipator has the advantages of high energy dissipation rate and small scouring, its underflow rate and fluctuating pressure is extremely high, which has restricted the development of underflow energy dissipation. The way the nappe arrived at the slob is similar to submerged water jet flow. There are two large vortexes near the nappe. The value of hydraulic parameters are reduced by "water cushion" between the nappe from the chute and the slab.In order to study the hydraulic characteristics of stilling basin with drop sill, the underflow speed, time average pressure, impact pressure, fluctuating pressure and uplift force are analyzed by the model test of one engineering project with the scale of 1:50 and numerical simulation. Based on the results, the influence of shape parameters on hydraulic characteristics are analyzed by changing the shapes, which can provide references for engineering projects. The main results and conclusions are as follows:1. According to the results from numerical simulation, we point out that the pressure force on the drop section does not exactly obey the hydrostatic pressure distribution. By adopting Katakam’s methods, expressions are obtained for the sequent depth ratio and energy dissipation rate based on the momentum and energy equations. By means ofπ-principle, the relationship between the maximum of underflow hydraulic characteristics and the shape parameters are established.2. Under the condition of low flow rate, mixture flow can be seen. As the flow rate becomes higher, the mixture flow changes to underflow. Due to the drop sill, impact pressure appears at the head of the basin, which seems to that of ki-jump or drop. The value of it has a positive linear relationship with the ratio of flow rate and water head. The fluctuating pressure reaches maximum at the impact point, which is lower about 50% than that of conversional stilling basin. And the uplift force is lower about 5～9%. When refers to changing the shapes, changing the hight of drop and the intake angle of jet flow cause greater influence on hydraulic characteristics.3. The range of eddy motion is affected by changing the slop of drop. Changing the height of the drop exerts an effect on the trajectory of the jet. And different lengths of basin have different volume of water body for energy dissipation. The relative curves between the shape parameters and hydraulic characteristics are obtained based on curve-fitting calculation data. We discovered that when the shape parameters exceed limits, the maximum hydraulic parameters will keep constant.