槽道湍流在确定分布的展向电磁力调制下的壁面减阻机理

Turbulent Drag Reduction in Channel Flow Modulated by Spanwise Lorentz Force with Steady Distribution

关键词:  槽道湍流  直接数值模拟  湍流减阻  电磁力  雷诺应力

Key words:  Turbulent channel flow  Direct numerical simulation(DNS)  Turbulent drag reduction  Lorentz force  Reynolds stress

摘要:

为了研究槽道湍流中确定分布的展向电磁力的流动控制与减阻问题，采用直接数值模拟的方法，对槽道湍流的确定分布展向电磁力控制后的流场中流向脉动速度、法向脉动速度以及雷诺应力分布的变化规律进行了研究。研究结果表明，槽道湍流流场存在大量分布紊乱的准流向涡和发夹涡结构，经过确定分布的展向电磁力调制之后，该流场的发夹涡结构基本消失，仅存在规律分布的准流向涡结构。控制后的流场相比于湍流流场，其流向脉动速度和法向脉动速度均受到了束缚作用，尤其是近壁区域更为明显。整个控制过程的实质是雷诺应力离散点向原点集中的过程，这个过程导致了流场雷诺应力和壁面阻力的下降。

Abstract:

The flow control and drag reduction in turbulent channel flow modulated by spanwise Lorentz force with steady distributions were carried out by direct numerical simulation (DNS). The characteristic of normal fluctuation velocity，streamwise fluctuation velocity as well as the Reynolds stress distribution were discussed. The results suggest that，in the turbulent channel flow，there are all kinds of streamwise vortices and hairpin vortices which distribute irregularly. After the Lorentz force induced，the hairpin vortices almost disappeared，and streamwise vortices distribute regularly. Besides，the normal fluctuation velocity and streamwise fluctuation velocity have an effect of reducing fluctuation intensity，especially in the near-wall area. During the whole control process，the changes lead to the distribution of Reynolds stress concentrating near to the origin which results in the reduction of Reynolds stress and the skin friction in the flow field.