电磁力减振过渡过程的机理研究

电介质溶液中，电磁场产生的电磁力可以控制流体的运动。将其用于钝体绕流时，可以抑制分离和消除涡街，从而达到减振的目的。为了研究电磁力减振的过渡过程，将指数极坐标系建立在运动的圆柱上，推导了运动坐标中，基于涡生振荡并考虑电磁力的涡量-流函数守恒方程及其初始和边界条件，圆柱表面的水动力表达式以及圆柱振荡方程。对圆柱从静止开始振荡，到发展为稳定振荡状态，然后又在电磁力作用下衰减，直至成为新的稳定态发展过程进行了计算和讨论，描述了圆柱振荡、脱体涡街和能量传递的发展过程，以及升阻力相图的连续变形和漂移。结果表明：圆柱振动的诱因在于流动分离产生的尾涡诱导的升力周期变化；圆柱表面附近分布的切向电磁力可以有效改变边界层附近流体的流动，抑制流动分离，从而使流场趋于对称，消除升力的周期振动，最终抑制圆柱的振动甚至在电磁力较大时可以消除振动。

Mechanism Investigation on Transient Process of Oscillatory Suppression by Lorentz Force

The flow of weak electrolyte solution can be controlled by Lorentz force generated by the suitably-chosen electromagnetic field. Lorentz force can be used to suppress the vortex shedding and eliminate the vortex street in the flow around a bluff body for the suppression of vortex-induced vibration (VIV). To investigate the evolutions of VIV suppression by Lorentz force, an exponential polar coordinate system is set up on a moving cylinder, and the stream function-vorticity equations considering the Lorentz force and its initial/boundary conditions, an expression of hydrodynamic force on the cylinder surface as well as the cylinder response equations are then derived. The whole evolutions of cylinder from resting and then undergoing development and suppression due to Lorentz force are calculated and discussed. The development process of cylinder vibration, vortexes shedding and energy transfer, and the deformation and shift of drag-lift phase diagram are described. The results show that the reason of cylinder oscillation is the periodic vibration of lift which is induced by wake vortexes due to flow separation. The fluid flow near boundary layer is changed and the flow separation is suppressed by the Lorentz force on the surface of cylinder so that the flow field tends to symmetry and the periodic vibration of lift is suppressed. The cylinder oscillation can be suppressed and even eliminated for a large value of Lorentz force.