进水池表面吸气涡数值模拟与试验

Numerical Simulation and Experiment on Free-surface Air-entraining Vortices in Pump Sump

为了有效地消除表面吸气涡,对进水池内流场进行了数值计算,模拟了表面涡吸气的动态过程;建立了试验模型,验证CFD方法的可靠性;并提出了圆形盖板消涡装置,探求其有效性;采用了螺旋度密度分析法,揭示了表面涡的吸气及其抑制机理。结果显示:采用的CFD方法可以较好地预测表面吸气涡的动态过程;吸气准备阶段,自由水面出现凹陷,喇叭管进口附近形成螺旋度密度管;随着气体从自由水面进入水体,自由水面下方形成另一螺旋度密度管;当连续气柱形成时,两个螺旋度密度管相互连通,形成气体通道;通过在自由水面和喇叭管进口之间放置一定尺寸的圆形盖板装置,可以消除表面吸气涡。

In order to suppress the free-surface air-entraining vortex in pump sumps, the threedimensional unsteady vortex flow in a pump sump was calculated by computational fluid dynamics（ CFD）method. The dynamic process of the free-surface air-entraining vortex was simulated. And an experimental model was conducted to verify the CFD method. In this experimental model,a circular plate device was placed between the free surface and the inlet of the bell-mouth to suppress the air entrainment. Furthermore,a parameter called helicity density was adopted to reveal the mechanism of air-entrainment and its suppression. The results showed that the numerical method used in this study can predict the dynamic process of air-entrainment for the free-surface vortex accurately. The helicity density played a very important role in the formation of air entrainment. When the dimple appeared on the free surface,a helicity density tube was formed around the inlet of the bell-mouth. As air entered into water,the other helicity density tube was formed under the free surface. When the two helicity density tubes were connected with each other,the air-core from the free-surface to the inlet of the bell-mouth was formed. This meant that the mechanism of air-entrainment for the free-surface vortex was the connection of the helicity density tubes which provided a passage for air to pass through. Moreover,the circular plate with enough dimension can successfully suppress the air-entrainment through cutting off the helicity density tubes.