进水池表面吸气涡数值模拟与试验

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。

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

In order to suppress the free-surface air-entraining vortex in pump sumps, the three-dimensional 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.