Study On Numerical Simulation Of Flow Field Of Stepped Overflow Dam Based On The Gradient Of Stepped Surface

Stepped spillway dam is a new type of energy dissipator which designs a series of steps from the breast wall to the dam toe.The well-designed stepped spillway can make the flow energy dissipate a lot in the stepped section,and then can significantly reduce or even completely save the stilling basin,and obtain huge economic benefits.In this paper,with the help of ANSYS finite element analysis software,on the basis of a model test enlarged and improved dam body,especially in view of the phenomenon that the energy dissipation rate of stepped overflow dam decreases with the increase of upstream flow,four optimization schemes are proposed,and the energy dissipation rate,flow field vector,turbulent energy,dam surface pressure and other factors under the influence of optimized structure are compared and studied.The main research contents and results are as follows:(1)The finite element model of the stepped spillway dam is established.Taking the different flow rate on the stepped surface as variable(controlled by the boundary condition of the inlet),the flow situation of water gas two-phase flow on the dam surface is simulated.The flow field near the stepped surface is focused on,and the formation process of the inner roll of the stepped surface corner is simulated.The simulation results show that with the increase of the flow into the corner,the flow in the concave corner will gradually appear obvious rolling.For the concerned energy dissipation rate,through the calculation and comparison of the downstream energy dissipation rate,it is found that with the increase of the flow on the step surface,the energy dissipation rate decreases rapidly.(2)Based on the simulation results of water gas two-phase flow in the fluid domain,an attempt is made to combine a bucket structure similar to a tail-ridge with a stepped spillway dam and recalculate the energy dissipation rate.The results show that the energy dissipation effect can be effectively increased and the trend of energy dissipation rate decreasing with the increase of flow rate can be slowed down by the appropriate shape optimization measures;(3)At the same time,the factors such as turbulent kinetic energy and turbulent energy dissipation under the action of step surface discharge flow after adding energy dissipation measures are studied,and the reasons for the change of energy dissipation rate are explored.The comparison results show that the local loss and high turbulent energy area are easy to appear near the bucket structure,which is the important reason for the change of energy dissipation rate(4)Combined with the results of flow field calculation and fluid structure coupling method,the pressure distribution on the dam surface and the mechanical properties of the improved structure are studied,and the improved structure is evaluated.(5)Based on the above results,the original optimization scheme is further improved,and the number of ridge structures in the original optimization scheme is reduced.Finally,the better energy dissipation rate improvement effect is achieved,which alleviates the situation that the original improvement scheme has a large area of negative pressure area on the vertical solid wall of some steps.