竖轴旋涡对丁坝坝头块石颗粒起动的影响

研究丁坝坝头块石的走失原因对河道整治工程、路基桥梁等的经济和安全都有很重要的意义。通过采用静止流场中圆柱旋涡产生的流场与明槽均匀流动的叠加对流场进行了简化,分析了竖轴旋涡对块石颗粒的作用,并求解了在旋涡吸力及绕流升力作用下颗粒的瞬时起动流速;计算表明瞬时起动流速比时均情况下起动流速要小的多,解释了时均情况下难以起动的块体在旋涡瞬时吸力下能被卷走的原因;分析了坝长和束窄率对瞬时起动流速的影响,为进一步分析竖轴旋涡对坝前颗粒运动及局部冲刷的作用建立了基础。

Influence of vertical vortex on the initiation of rock motion

Research on the missing of rocks around spur dikes is of importance on the economy and safety of river regulating structures, roadbed and bridges. In this paper, the flow field around spur dikes is simplified by plus of flow field induced by cylindrical vortex in still water and uniform open channel flow. The action of the vertical vortex on the rock is analyzed and the transient incipient velocity of particles is solved under the action of the absorb force by the vertical vortex and the lift force. The presented analytical transient incipient velocity is much less than that in the time averaged case. It can explain why the huge rock is hard to initiate in the time averaged case but can be sucked away by the transient absorbing of the vertical vortex. The effect of the length of dike and protrusion ratio of river on the incipient velocity is analyzed, it sets up the foundation of evaluating the influence of vertical vortex on the local scour.