Multi-Layer Computation of Coupled Finite Volume Solution of Depth-Averaged Flow in Steep Chute Spillways Considering Air Concentration Effects

摘要

The results of numerical analyzing of air concentration distribution in the AVIMORE chute spillway are presented in this paper. In order to solve this phenomenon three modeling strategies are used: 1) Solving the flow parameters without considering the effects of free surface aeration and then computing air mean concentration by a separate post-processor. 2) Simultaneous solution the flow equations and computation of the air entrainment from the water free surface. 3) Adding the effects of variation in aerated water density to the numerical flow solver. Therefore, firstly, the free surface air entrainment mechanism on chute reviewed, and then, the numerical solution of shallow water equations in inclined coordinate system is described. The equations are converted to discrete form using the overlapping cell vertex and cell centre finite volume methods on a triangular unstructured mesh. The post-processor in the 1st modeling strategy uses relations for computing the inception point characteristics and air mean concentration as vertical well as distribution profiles along the chute. In the second modeling strategy the effects of free surface aeration on the bed friction coefficient reduction and depth bulking are considered at each computational step of flow solution. In the 3rd modeling strategy the effect of the water-air density variations is added to the momentum equations. The results are compared with observations on the AVIMORE chute spillway. Finally, the best experimental relations for simulating the entrainment of air into the flow on chute spillways have been chosen. In order to provide better understanding of the velocity and air concentration, the vertical distribution profiles of these parameters are plotted from the multi layer treatments of depth averaged computed results.