增设收缩墩后的跌坎消力池三维流场研究

当消力池池长和池宽受到限制时,跌坎底流消能工在大单宽流量、低Fr来流条件下引起的振荡水跃对消力池具有较大的破坏力;模型试验研究发现,在跌坎消力池前采用收缩墩后的联合消能工可有效解决上述问题。选取RNG k-ε模型和流体体积函数法(Volume of Fluid,VOF)自由液面追踪法,构建有无收缩墩2种跌坎消力池并进行数值模拟,得到流场内的水力特性,并结合试验数据对有无收缩墩的2种跌坎消力池方案进行对比分析。结果表明:跌坎消力池池内紊动能不足和大尺度漩涡的不稳定性是引起振荡水跃的主要原因;设置收缩墩后水流经收缩墩横向收缩和纵向拉伸后形成收缩射流,在消力池内形成2条细长的强紊动区,形成了更多三维漩涡,漩涡尺度变小,紊动剪切加剧,破坏了不设收缩墩时的水跃旋滚,有效地消除了振荡水跃。这种消能工对工程条件限制下的低Fr数、大单宽流量底流消能具有较高的推广应用价值。

Three-dimensional Numerical Simulation of Turbulent Flow with Contraction Jet in Stilling Basin with Step-down Floor

The oscillating hydraulic jump caused by the inflow condition of large single width and low Froude number in energy dissipator for falling-sill bottom-flow has great destructive force to stilling basin of which the size is limited. A joint energy dissipator with a contraction pier in front of the pool has been tested on a hydraulic scale model and proved to have solved the problem effectively. The RNG k-ε model and VOF method were employed to construct two models of stilling basin in the presence and in the absence of contraction pier. The hydraulic characteristics were obtained from the 3D numerical simulation. And the stilling basins in the presence and in the absence of contraction pier were compared in association with hydraulic scale model test data. Results unveiled that insufficient turbulent energy and unstable large-scale eddies are main causes of the oscillating hydraulic jump in the stilling basin with step-down floor. In the presence of contraction pier, two high turbulence intensity areas are formed in the stilling basin. More 3D eddies of smaller scale were formed, enhancing the turbulence intensity and shear strength, disrupting the large-scale eddies of water jump and eliminating the oscillating hydraulic jump effectively.