明渠砂质床面桩柱冲刷与导流防护试验研究

为了研究明渠砂质床面桩柱冲刷的水沙动力机理,分析极限平衡冲刷深度和范围随水流雷诺数的变化规律以及抗冲刷导流防护措施的效果,利用动床模型水槽试验,再现了桩柱周围局部床面从平整发展到冲刷坑的发育过程,测量了各工况下冲刷坑的形态参数,并利用PIV技术观测粗颗粒泥沙局部悬扬运动。结果表明:桩柱冲刷范围(相对于桩径D)随雷诺数ReD增大呈减小趋势。当雷诺数ReD在4 500~18 000之间变化时,冲刷深度变化范围为2.4D~1.3D,冲刷坑半径变化范围为4.5D~2.5D。砂质床面桩柱冲刷除存在显著的推移质运动外,还存在局部粗泥沙颗粒悬扬,且悬扬输沙的范围和强度随冲刷坑发展而强烈变化。在桩柱后方设置导流板能够有效抑制柱后卡门涡街的生成,桩后冲刷深度最大减小幅度为27.7%,但对柱前冲刷深度的影响不大。

Experimental study on scouring around pile-column in sand-bed of open channel and relevant flow guiding protection measure

In order to study the flow-sediment dynamic mechanism of the scouring around pile-column in sand bed of open channel and analyze the law of the variation of the ultimate balanced scouring depth and range along with Reynolds number and the effect of the relevant anti-scouring flow guiding protection measure, a movable-bed model flume experiment is made, from which the developing process of the local bed surface around pile-column from smoothness to scouring pit is reproduced, and then the parameters of the geometric configuration of the scouring pit under all the working conditions are measured, while the local suspension movement of coarse grained sediment is observed with PIV technique as well. The result shows that the scouring range around pile-column ( relative to the diameter of the pile-column, D) presents a trend of decreasing along with the increase of Reynolds number ReD. When Reynolds number ReDvaries from 4 500 to 18 000, the range of the scouring depth variation is 2. 4 D 1. 3 D with the variation range of 4. 5 D ~ 2. 5 D for the radius of the scouring pit. For the pile-column in sand bed, the local suspension of coarse grained sediment is there, besides significant bed load movement, while the range and strength of the suspended sediment transport are strongly varied along with the development of the scouring pit. Arranging flow guiding plate behind the pile-column can effectively restrict the formation of Karman vortex streets therein with the maximum reduction amplitude of 27. 7% for the scouring depth behind the pile-column, but the effect on the scouring depth in front of the pile-column is less.