Three-Dimensional Simulation Of The Stepped Spillways With Aerators

Energy dissipation rate can be improved with the stepped spillway by taking advantage of roughness of steps and strong rotation of flow, but the possibility of cavitation damage on walls is increased because of the large non-flatness.It has become an important research for the stepped spillways on increasing aeration facilities to avoid cavitation damage.Therefore,the bucket aerator is set on the first step to prevent cavitation in this paper, which is very important for the application of stepped spillways.The structured/unstructured hybrid grids were adopted to divide computational domains,and the RNG k-s turbulence model and the VOF method were used in calculation.The hydraulic characteristics of flow on stepped spillways with aerators have been obtained by the three-dimensional numerical simulation. The main work is as follows:water profiles of stepped spillways at different times and in different conditions,the distribution of velocity contours and cross-section velocity, the pressure distribution on horizontal planes,the pressure distribution on vertical planes and the on-way pressure distribution, the local and on-way distribution of turbulent energy and turbulent dissipation rate,the comparative analysis of energy dissipation rate in eight kinds of operating conditions,the calculation of the cavity length and the aerate amount of blowholes.Research results show that when water flows through aerators,the water surface is elevated and the water tongue collides with the steps to form a contracted cross-section after it across several stairs down to the dam surface. At the same time,water rebounds and water surface rises again. Subsequently, the water on each step has a vortex along the clockwise. The slip mainstream above the vortex parallels to the virtual floor.The flow pattern is adjusted to the water flow on typical stepped spillways gradually.The flow velocity of stepped spillways is close to zero at the vortex center and is gradually increasing from vortex center to around,but it is less than the velocity of the slip mainstream.On the virtual backplane connected by convex corners, the mainstream velocity is gradually increasing along the outer normal direction of spillways, but the process of increasing is relatively moderate,when it increases to the maximum value,the velocity on cross sections reduces slightly.The pressure distribution rules of stepped spillways:the pressure reduces to the minimum value and then gradually increases to the maximum value from concave corners to convex corners,at last it reduces again near the convex corners and there is negative pressure on horizontal planes in several steps. There is the maximum positive pressure at the bottom of vertical planes of steps,the pressure becomes smaller upward gradually. And it is near to zero at 0.7-0.8 time relative heigh from the bottom of steps,the minimum value of negative pressure appears at about 0.85-0.95 time relative height from the bottom of steps.The shape of pressure distribution likes wave along the way.Due to the negative pressure on step surfaces,it is possible to lead to cavitation damage on stepped spillways.Therefore,air entrainment for stepped spillways is very important.There is a maximum value area of turbulent energy in steps which is located in the middle of the virtual backplane.There are three local maximum areas of turbulent dissipation rate which include the vicinity of the convex corners on horizontal faces which is the largest value area,the vicinity of the convex corners on vertical faces and the cross-interface of vortex and mainstream. The calculation result shows that, compared with smooth spillways,energy dissipation rate of the stepped spillways have increased 46.9-65.4%.There is a cavity area upon dam surface when the aerator is located on the stepped spillway. The calculated value of cavity length is very close to the measured value, which both decrease with the upstream waterhead increasing and increase with the slope grade increasing.However,there is a large difference between the calculation value and the measured...