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现有实验测量和数值模拟方法难以准确捕获近水面流动特征,为全面掌握墩柱上游行近来流的内部结构和水面特征,通过明渠圆柱绕流试验,采用粒子图像测速技术对柱体上游的对称垂面进行了测量,获得了行近来流的瞬时二维流场和水面线。在此基础上,对圆柱上游的时均流动和壅水特征进行了研究,得出上游行近来流从水面至床面依次由上升流、近水平流和下降流构成,形成典型的三层结构,其中,上升流厚度随柱体雷诺数增加而变厚,下降流无量纲厚度基本不随柱体雷诺数改变。在靠近柱体的床面附近,边界层与床面分离,分离区内为向上游流动的逆流以及一个马蹄涡和一个次生涡;在靠近柱体的水面附近存在表层逆流以及两个逆向涡。研究结果揭示出边界层分离、表层逆流及柱体本身依次促使行近来流减速,使得沿程水深雍高,壅水末端至圆柱迎水面的水面线符合一元四次函数分布,无量纲壅水长度随着柱体雷诺数的增加而延长。研究成果可作为基于流体体积法等具有自由水面计算能力的明渠墩柱绕流数学模型的验证依据。
In order to fully grasp the internal structure and water surface characteristics of the recent flow on the pier, the flow around the open channel is experimentally tested, and the particle image velocimetry is used to measure the symmetry of the upstream of the column The vertical plane was measured and the instantaneous two-dimensional flow field and water surface line were obtained. On this basis, the characteristics of time-average flow and water flushing in the upstream of the cylinder were studied. It was concluded that the upstream flow from the water surface to the bed surface was composed of upward flow, near-horizontal flow and descending flow, forming a typical three-layer structure , In which the thickness of upwelling flow becomes thicker with the increase of Reynolds number of the cylinder, and the non-dimensional thickness of the descending flow basically does not change with the Reynolds number of the cylinder. In the vicinity of the bed near the column, the boundary layer is separated from the bed surface, the upstream of the separation zone is a reverse flow and a horseshoe vortex and a secondary vortex. In the vicinity of the surface of the column, there are surface reverse flow and two reverse vortices . The results show that the separation of the boundary layer, the superficial turbulence and the cylinder itself in turn lead to the recent deceleration of the flow, which makes the water depth along the Yong Yonggao line and the water line from the end of the Huangshui to the cylindrical Yinggui line conform to the quadratic quadratic function distribution. The dimensionless water length As the cylinder Reynolds number increases. The research results can be used as the verification basis of the mathematical model of the flow around the open channel pier based on the free-surface calculation of fluid volume method.