串列双锥柱绕流流动特性的大涡模拟研究

LARGE EDDY SIMULATION OF FLOW PAST TWO CONICAL CYLINDERS IN TANDEM ARRANGEMENT

利用大涡模拟研究了雷诺数Re=3900下串列双锥柱在间距比L/D;=2~10下的升阻力特性及三维流动结构.研究发现:上游锥柱在后方形成的两个展向不对称回流区,使其后方压力分布不对称.上游锥柱发展的上洗、下洗和侧面剪切层作用在下游锥柱的附着点位置不同是上游和下游锥柱时均阻力系数和脉动升力系数变化的主要原因,串列双锥柱间流动结构随间距比变化可分为三种状态:剪切层包裹状态,过渡状态及尾流撞击状态.剪切层包裹状态.上游锥柱的自由端主导来流在下游锥柱迎风面影响范围广,上游锥柱剪切层完全包裹住下游锥柱,从而抑制下游锥柱后方回流区形成,导致下游锥柱时均阻力系数降低;尾流撞击状态;上游锥柱尾流得到充分发展,其回流区大小随间距比增大不再发生变化,上游锥柱尾流出现周期性脱落,撞击在下游锥柱表面,从而使脉动升力系数大幅增加,最大脉动升力系数较单直圆柱提升约20.7倍;过渡状态,此时时均阻力系数和脉动升力系数均会较剪切层包裹状态增加.该研究可以为风力俘能结构群列阵布局提供理论支持.

In order to explore the time-averaged drag coefficient,fluctuating lift coefficient characteristics and flow field mechanism of two conical cylinders in tandem arrangement,large eddy simulation is used to simulate two conical cylinders in tandem arrangement with a spacing ratio of 2-10 at Re=3900.The two spanwise asymmetric reflux zones formed behind the upstream conical cylinder make the en dash pressure distribution behind it asymmetric.The upwash,downwash and side shear layers developed by the upstream conical cylinder are the main reasons for the variation of the time-averaged drag coefficient and the fluctuating lift coefficient of the upstream and downstream conical cylinders.The flow structure between tandem two conical cylinders can be divided into three states with the change of spacing ratio:in the shear layer wrapping state,transition state and wake impact state.Shear layer wrapping state,the dominant incoming flow at the free ends of the upstream conical cylinder has a wide range of influence on the windward side of the downstream conical cylinder.The shear layer of the upstream conical cylinder completely wraps the downstream conical cylinder,inhibiting the formation of the backflow zone behind the downstream conical cylinder,causing a decrease in the time-averaged drag coefficient of the downstream conical cylinder.In the wake impact state,the wake of the upstream conical cylinder is fully developed,and the size of the recirculation zone does not change with the spacing ratio.The wake of the upstream conical cylinder periodically falls off and hits the surface of the downstream conical cylinder,which greatly increases the pulsating lift coefficient.The maximum fluctuating lift coefficient is about 20.7 times higher than that of a single straight cylinder.In the transition state,the time-averaged drag coefficient and the fluctuating lift coefficient will both increase compared with the shear layer wrapped state.This research can provide theoretical support for the layout of wind energy harvesting structures.