槽道壁湍流的展向振荡电磁力减阻控制的PIV研究

PIV study of drag reduction in the near-wall turbulent channel flow under the control of spanwise oscillating Lorentz force

壁湍流主要表现为条带和流向涡为主要特征的拟序结构和间歇性的湍流猝发事件,这些都会导致壁面阻力的增加,因此,为了实现减阻,需控制或消除壁面附近的流向涡进而抑制湍流的猝发。在该研究中,利用展向振荡电磁力对槽道湍流的近壁流向涡进行控制,以达到减阻的目的;并利用PIV测试系统对其进行了实验研究,讨论了这种电磁力的减阻效果及其减阻机理。结果表明:展向振荡电磁力具有减小壁面阻力的功能,其减阻机理为展向振荡的电磁力可以使条带倾斜,在流场中产生附加的负展向涡,导致近壁区域平均流向速度梯度的减小,因此,壁面阻力减小。

The feature of near-wall turbulence is showed by intermittent turbulent burst events and coherent structures whose main characteristics are streaks and streamwise vorticity.The intermittent turbulent burst events and coherent structures will lead to near-wall drag increase;therefore,in order to achieve the drag reduction,we need to control or eliminate the streamwise vorticity in the near-wall area,and then control the turbulent burst.In current studies,in order to achieve the drag reduction,we used the spanwise oscillating Lorentz force to control the streamwise vorticity in the near-wall region,used the PIV test system to carry out an experimental studies and discussed the drag reduction effects and mechanism of such kind of Lorentz force.The results show that the spanwise oscillating Lorentz force has the function of drag reduction,and the mechanism of drag reduction when applied spanwise oscillating Lorentz force is this type of Lorentz force which can make the streaks incline and generate the additional negative spanwise vortex in the flow field,and this will decrease the average streamwise velocity gradient in the near-wall region which lead to the drag reduction.