确定分布的展向Lorentz力调制下的槽道湍流涡结构

采用直接数值模拟方法,对槽道湍流中确定分布的Lorentz力的流动控制与减阻问题进行研究.讨论了Lorentz力作用于槽道湍流后,流场的特性和涡结构的特性,并对此类Lorentz力对槽道湍流的控制与减阻机理进行了讨论.研究发现:1)Lorentz力诱导的层流流场壁面附近存在梯度极大的展向速度剪切层,该剪切层容易形成流向涡结构;2)在给定合适参数的确定分布的Lorentz力作用下,湍流流场仅剩周期分布的准流向涡;3)与未控制流场相比,控制后的流场中,准流向涡的抬升高度大大降低,从而减小猝发强度,使壁面阻力下降.

Vortex structures in turbulent channel flow modulated by a steadily distributed spanwise Lorentz force

Turbulence control and drag reduction in a channel flow by using a steadily distributed spanwise Lorentz force are investigated numerically via a direct numerical simulation (DNS). The characteristics of controlled flow fields and vortex structures are described. Meanwhile, the mechanisms of turbulence suppression and drag reduction by the Lorentz force are also discussed. Calculated results indicate that: (1) The shear layers with a arge gradient of spanwise velocity are created in the laminar boundary layer induced by the spanwise Lorentz force, where the streamwise vortices are easily generated by perturbations. (2) Under the action of the distributed Lorentz force with proper control parameters, only periodically well-organized streamwise vortices are observed in the near-wall region of the turbulent channel flow. (3) After controlling, the averaged lift height of inclined streamwise vortices is reduced significantly as compared with the uncontrolled turbulence flow, resulting in the reduction of the burst strength and subsequent drag reduction on the wall.
Keywords： turbulent channel flow direct numerical simulation (DNS) drag reduction Lorentz force