分层强剪切环境下减阻板对圆柱减阻效应研究

Drag Reduction Effect of Splitter Plate on Cylinder in Stratified Strong Shear Environment

由于上下水层流动反向,柱体在分层流环境中与密度均一流环境中受力差别较大。将密度均一流环境下上游减阻板对柱体减阻的概念引入分层流环境下的圆柱受力研究中,建立三维数值模型,采用大涡模拟(LES)技术,研究内波环境下圆柱的减阻效应。结果表明:在上层水体中,减阻板对柱体受力影响较大;在下层水体中,减阻板几乎不起作用。减阻板背部的漩涡形态是影响柱体减阻效应的根本原因。减阻参数(阻塞比l/D及“板-柱”间距s/D)决定了柱周漩涡结构特征,直接影响减阻效果。引入减阻比B_(R)量化了减阻效果,采用回归分析拟合出B_(R)与s/l的经验公式。需将减阻参数控制在合理范围内,避免发生“减阻过度”。研究成果对提高近岸及河口建筑物墩柱安全有重要意义。

Forces on cylinder in stratified flow environment differs notably with those in uniform density flow due to the opposite velocity directions of two layers.A splitter plate deployed upstream of the cylinder in uniform density flow with its frontal face normal to the wave propagation is employed to explore the reduction of forces on an erected cylindrical pile.A 3-D numerical wave flume model is established to investigate the reduction of forces acting on cylinder through Large-Eddy Simulation(LES)approach.Results unveil that splitter plate has prominent influence on the force distribution of the pile in the upper layer,but hardly any effect on the counterpart in the lower layer.The pattern of vortex structure behind the splitter plate plays a fundamental role in reducing the drag forces on pile.Key parameters blockage ratio l/D and plate position ratio s/D characterize the feature of vortex structure around the pile.The reduction effect is quantified by forces reduction ratio B_(R),and an empirical formula between B_(R) and s/l is fitted by regression analysis.The parameters of splitter plate should be controlled at an appropriate level to prevent from over-reduction.