梯形凹角台阶式溢洪道水力特性

台阶式溢洪道中凹角水流的循环及能量交换是泄洪消能的关键因素之一,目前台阶式溢洪道的研究多集中在台阶的坡度、尺寸以及与宽尾墩等联合运用方面,鲜有对台阶凹角几何形状进行研究。通过水工模型试验和数值模拟计算,对传统三角形凹角台阶和新型梯形凹角台阶的流态、掺气浓度、压强、流速等水力特性进行研究,结果表明:梯形凹角台阶与三角形凹角台阶水流水力特性分布规律相同,但由于梯形凹角台阶改变了旋涡脱落的形状,漩涡脱落进入主流中,促进水流湍动,使得初始掺气点位置略微前移,增加主流区断面平均掺气浓度,提高虚拟底板处总压强波动强度,降低台阶沿程流速,有利于提高台阶抗空化空蚀能力和促进台阶消能。

Hydraulic Characteristics of Stepped Spillway with Trapezoidal Concave Angle

The flow circulation and flow energy exchange in the concave angle of stepped spillway is a key factor of flood discharge and energy dissipation. Current research of stepped spillway mostly focus on the combined actions of step’s slope and size as well as wide tail pier; the geometric shape of concave angle is rarely studied. In this paper, the flow pattern, flow velocity, intensity of pressure and concentration of entrained air in both traditional triangular concave angle steps and trapezoidal concave angle steps are examined via hydraulic model tests and numerical simulated calculations. Results demonstrated the similarity of flow state between trapezoidal concave angle steps and traditional triangular concave angle steps; but trapezoidal concave-angle step changes the shape of vortex shedding, which, therefore, moves into the main flow and promotes the turbulence of water flow. As a result, the initial point of aeration moves slightly forward, the average concentration of entrained air in the cross section of the main flow area increases, the total pressure fluctuation at the virtual bottom plate intensifies, and the average flow velocity of the step section reduces, beneficial to reducing the risk of step cavitation and promoting the energy dissipation of the step.