圆柱绕流局部冲刷机制的实验研究

采用粒子图像测速技术和粒子图像识别技术研究了冲刷坑的演化过程及局部冲刷的流体动力机制。首先研究了动床条件下圆柱周围的床面演化过程，给出垂直对称面输沙率随时间变化以及圆柱下游垂直对称面的沙颗粒浓度和泥沙分布规律；其次针对典型冲刷坑形状固定底床，测量了圆柱下游的瞬时流场，并给出平均流场。结果表明尾流区平均剪应力较低，但垂向涡量和湍流强度较高。分析指出平均剪应力较低的尾流区域，局部冲刷的主要动力机制是尾涡和湍流的综合作用。

EXPERIMENTAL INVESTIGATION ON THE LOCAL SCOURING MECHANISM AROUND A CIRCULAR PIER

In this paper, the development of the scour hole and the mechanism of the local scouring around a vertical circular pier are investigated experimentally with DPTV and the Particle Mask Correlation Method. First, the bed evolution is studied using the mobile bed, and the rate of the sediment transport along the centerline, the law of the particle concentration and the sand distribution in the symmetry plane downstream of the pier are obtained. Second, the instantaneous velocities are measured under the condition of fixed beds corresponding to the mobile beds of scour, and also the mean flow fields are obtained. The experimental results show that in spite of the fact that the bed shear stress is low during erosion in the wake, the vertical vorticity and the turbulence intensities are high. So besides the bed shear stress, the wake vortices, the negative pressure and the turbulent intensities also contribute to the mechanism of the local scouring.