O型套环对圆柱结构气动力和干索驰振影响的试验

Experimental Study on the Effects of O-rings on Aerodynamic Forces and Dry Galloping for Cylindrical Structures

圆柱类结构在土木工程领域应用十分广泛,其风荷载和风致振动一直是研究和设计十分关注的问题。根据圆柱结构风致振动的机理,提出了O型套环这种被动式的三维气动措施,并对其减阻抑振效果进行了全面研究。通过风洞内的天平测力和干索驰振试验,研究了O型套环的几何参数(间距、宽度和厚度)对气动力和干索驰振的影响规律,并对减阻抑振机理进行了分析。研究结果表明:同标准圆柱类似,套环圆柱的平均阻力系数和雷诺数密切相关;当雷诺数小于3.0×10^(5)时,套环圆柱的平均阻力系数小于标准圆柱的结果,最大减阻率为29.5%;当雷诺数大于3.0×10^(5)时,套环圆柱的平均阻力系数大于标准圆柱的结果,最大增阻率为36.4%;标准圆柱和套环圆柱均会在高风速区间发生干索驰振,套环间距越小、宽度越大、厚度越小,对干索驰振的抑制效果越好;在亚临界区,套环圆柱可以减小阻力,原因是圆柱安装套环后,尾流宽度变窄,旋涡形成区变长,流场呈现三维特征;在临界区,套环圆柱会增大阻力,一定程度上可将套环视为对流场的扰动,加剧层流向湍流的转捩;套环圆柱对干索驰振的抑制和加剧与套环圆柱在临界区增阻的机理相似。

Cylindrical structures have been extensively used in civil engineering.Therefore,wind loads and wind-induced vibrations have always been the focus of research and design.Based on the mechanisms of wind-induced vibrations of cylindrical structures,a passive three-dimensional aerodynamic countermeasure,that is,O-rings,is proposed.Moreover,its effectiveness has been studied comprehensively.Through aerodynamic force and dry galloping measurement tests in a wind tunnel,the effects of the geometrical parameters(spacing,width,and thickness)of the O-rings on the aerodynamic force and dry galloping characteristics were investigated.Additionally,the underlying mechanisms of drag reduction and suppression of dry galloping were analyzed.The results show that similar to a standard cylinder,the mean drag coefficient of the ring-attached cylinder depended highly on the Reynolds number.When the Reynolds number was less than approximately 3.0×10^(5),the mean drag coefficient of the ring-attached cylinder was smaller than that of the standard cylinder,and the maximum reduction was 29.5%.When the Reynolds number was larger than approximately 3.0×10^(5),the mean drag coefficient of the ring-attached cylinder was larger than that of the standard cylinder,and the maximum increase was 36.4%.Dry galloping occurred in the standard and ring-attached cylinders.In general,control of dry galloping improves with decreasing spacing,increasing width,or decreasing thickness.The ring-attached cylinder reduced the drag in the subcritical regime.After the installation of the O-rings,the wake flow width became narrower,the vortex formation region elongated,and the flow field exhibited three-dimensional properties.The ring-attached cylinder increased the drag in the critical regime.To some extent,O-rings can be treated as perturbations to the flow field,which promotes the transition from laminar to turbulent flow.The mechanism for suppressing or intensifying dry galloping for ring-attached cylinders is similar to that for increasing drag in the critical regime.