力学所Seminar 787
主题：Active control of turbulence and fluid-structure interactions (湍流和流动结构相互作用的主动控制)
报告人：周裕 教授 (哈工大深圳研究生院湍流研究所)
时间：2013年12月5日（周四)13:30
地点：延长校区应用数学和力学所会议室
主办部门：理学院力学所

ABSTRACT：Turbulent flow control has attracted a great deal of attention in fluid dynamics community due to
its fundamental and technological significance. This talk presents a compendium of recent progress in the active control of flow and fluid-structure interactions in my group. Presentation will be largely focused on the turbulent 2D bluff body wake, jet, flat plate boundary layer and vehicle aerodynamics. Our early actuation technique for flow control deployed piezoelectric ceramic actuators to create a local perturbation on the wall, over which flow blows. This local perturbation alters fluid-wall interactions, thus modifying the flow initial/boundary conditions. This technique has been applied to manipulate the fluid-structure interaction in a twodimensional cylinder wake, resulting in the complete  estroy of the Karman vortex street (Fig 1). It was also used to control the aerodynamics of an airfoil, flow-induced vibration, vortex-blade interaction, and flow-induced noise. Various control schemes have been investigated, including both open- and closed-loop controls. The latter further consists of one single feedback signal or a combination of multiple feedback signals. Success has been achieved to different degrees in all the applications in terms of vortex  ppression/enhancement, drag reduction, fluctuating lift impairment, vortex-induced vibration, aerodynamic noise reduction, etc. This actuation technique is further extended to manipulate a turbulent flat plate boundary layer.
One array of 12 or 16 discrete piezoelectric ceramic actuators was used to generate a transverse travelling wave. Various control parameters were examined, including the actuation amplitude, frequency and the wavelength of the transverse wave. A local drag reduction up to 50% was achieved at 35 wall units downstream of the actuator tip. Accordingly, more regularized but considerably smaller scale streamwise structures were observed under control (Fig 2). It is proposed that these highly regularized streamwise structures act to weaken or even completely break the connection between the large-scale streaky structures and the wall and interrupt the turbulence production cycle, thus reducing friction drag. A conceptual model of the drag reduction mechanism is proposed.