不同周期壁面局部微振动诱导边界层大涡结构

Coherent structures in a boundary layer induced by local vibration of walls with different periods

以平板边界层流动的Blasius解作为基本流场,利用直接数值模拟方法求解三维不可压缩N-S方程,研究了边界层中单个周期壁面局部微振动诱导大涡结构的过程.计算结果表明:壁面扰动完成时,周期为7.5,10和12.5诱导大涡结构的初始扰动速度与空间分布稍有差异.若周期为12.5,随着时间的增加,诱导形成的大涡结构扰动速度幅值不断增加,高低速条纹结构面积不断扩大;边界层近壁流向速度剖面存在较大拐点,雷诺应力明显大于周期为7.5和10的大涡结构.周期为7.5和10的诱导大涡结构较弱.壁面局部微振动可诱导边界层形成大涡结构,演化特性与局部微振动周期密切相关,周期越长,大涡结构强度也越大.

The Blasius solutions in a boundary layer of the flat plate were taken as the basic flows. The coherent structures in a boundary layer induced by local vibration at the wall with different periods were simulated by solving the 3D incompressible Navier-Stokes equations by means of direct numerical methods. The calculated results show that when the wall distribution is completed,the amplitude and distribution of the initial disturbance velocity of the coherent structures exhibit a bit difference when the period is 7.5,10 and 12.5. When it is 12.5,the amplitude of disturbance velocity of the induced coherent structures increases and the area of streaks with higher and lower speeds becomes larger and larger with the increase of time. There exits an inflexion at the near-wall streamwise velocity profile in the boundary layer. The Reynolds stress is obviously larger than that when the period is 7.5 and 10. When the periods are 7.5 and 10,the induced coherent structures are weak. The local micro-vibration at the wall may induce the generation of coherent structures in the boundary layer. Their evolution characteristics greatly relate with the period of local vibration,that is,the longer the period,the stronger the strength of the coherent structures.