电磁控制涡激振荡的实验研究

Experimental investigations on control of vortex-induced vibration by Lorentz force

利用电介质溶液中圆柱体侧表面附近分布的电磁场产生电磁力可有效改变流体边界层及尾涡结构。本文以减振为目标,对电磁力控制涡激振荡进行了实验研究。实验在转动水槽中进行,通过吊杆将装有电磁激活板的圆柱插在槽内液体中。吊杆上的应变片用于测试圆柱的升力,注入适当的染料用来显示流场。结果表明:对称电磁力作用下,脱体涡被抑制,从而使升力的振荡受到有效抑制,进而抑制圆柱的振动,双排方向相反的涡变为单排正负交错的涡。当电磁力足够大时,圆柱的振荡被完全消除,流场达到定常。

The Lorentz forces generated by electromagnetic fields on the surface of the cylin-der in the electrolyte solution may modify the structures of the flow boundary layer effectively.In this paper,control of vortex-induced vibration by Lorentz force is investigated experimentally which aims for vibration suppression.Experiments are conducted in a rotating annular tank filled with a low-conducting electrolyte.A long metal sheet was used as a flexible support to mount the cylinder with a 2cm diameter.The cylinder with an electro-magnetic actuator mounted on the surface is placed into the electrolyte.Force measurements have been carried out by strain gages attached to a fixed beam to which the cylinder is suspended and flow fields are visualized by dye markers.The results show that since the upper vortex and lower vortex are shed at upper and lower maximum displacement related to the cylinder,the vortex street formed is composed of two parallel rows with an opposite signs of the vortices.With the application of symmetrical Lorentz force the vortexes of cylinder are suppressed which leads to the suppression of lift oscilla-tory and then the vibration of cylinder is suppressed.The vortex street formed is composed of two parallel rows which turn to the composition of negative and positive staggered vortices. When the Lorentz force is large enough,the flow on the surface of the cylinder is accelerated by the Lorentz force which causes the flow separation point to move downstream and disappear grad-ually.Then,the vortexes move downstream away from the cylinder and the vibration amplitude of cylinder begins to decrease.The vortex shedding is suppressed fully and the vibration is decay-ed rapidly.Finally,the vibration is suppressed fully so that the flow field is steady.