弯道凹岸不同部位崩塌体对近岸水流结构影响的试验研究

Experimental study on the effects of slump block at different locations upon the flow structure near the outer bank

二元结构河岸失稳后,上部河岸发生崩塌并堆积在近岸,从而改变近岸水流结构并影响河岸二次侵蚀过程。为了探索弯道凹岸不同部位的崩塌体对近岸水流结构的影响,以长江中游石首河段为背景,开展概化模型试验,采用多普勒流速仪(ADV)精细测量崩塌体附近三维水流流速,并对比分析有无崩塌体时水流及壁面剪切力的变化规律。结果表明:位于顶冲点上游的崩塌体,使纵向流速最大区域远离凹岸,从而使崩塌体与河岸坡脚之间区域内的平均壁面剪切力减小;而位于顶冲点下游的崩塌体,使纵向流速最大区域靠近凹岸,从而使崩塌体与河岸坡脚之间区域内的平均壁面剪切力增大。研究成果丰富了对二元结构河岸侵蚀过程的认识,有利于河岸侵蚀模型的发展与完善。

When a composite bank fails,slump blocks deposit at the toe of the bank.This alters the flow structure near the bank and affects the bank erosion processes.To investigate the effects of slump block at different locations on the flow structure near the outer bank,a generalized model of Shishou reach was conducted.Acoustic Doppler Velocimeters(ADV)was used to precisely measure the three-dimensional flow velocities.Experimental results show that the slump block upstream of the head-on scouring point shifts the region of maximum streamwise velocity away from the outer bank and reduces the averaged bed shear stress between the slump block and the bank toe.In contrast,the slump block downstream of the head-on scouring point makes the region of maximum streamwise velocity closer to the outer bank and increases the averaged bed shear stress between the slump block and the bank toe.This study enriches the understanding of composite bank erosion process,and helps to develop and improve the erosion model of composite bank.