槽道湍流的法向与展向电磁力壁面减阻

Drag Reduction in Turbulent Channel Flow Utilizing Normal and Spanwise Lorentz Force

关键词:  湍流  直接数值模拟  法向与展向电磁力  固有流场  诱导流场  调制流场  减阻 

Key words:  Turbulence  Direct numerical simulation  Normal and spanwise Lorentz force  Natural flow field  Induced flow field  Modulation flow field  Drag reduction

摘要:

法向与展向电磁力可以有效调制湍流近壁流动及减少壁面摩擦阻力。为进一步揭示该方法的减阻机理,利用Fourier-Chebyshev谱方法,通过直接数值模拟(DNS),对槽道湍流的法向与展向电磁力控制和减阻问题进行了研究。结果表明,对于确定的流向波长λ⁺_x,存在最佳的电磁力强度St,使阻力降最大,最佳St与λ⁺_x成反比。法向与展向电磁力对湍流的控制过程实质上是一种由电磁力诱导的调制波对壁湍流的调制过程。在优化参数控制下,当法向与展向电磁力诱导的流场被用来调制固有的近壁湍流流场时,固有流场和诱导流场同时受到调制。在这种调制波作用下,调制流场逐渐主宰壁面边界层,这导致了壁面阻力的下降,平均减阻率最高可达8%。 

Abstract:

Near wall turbulence and skin friction drag can be modified effectively via normal and spanwise Lorentz force. In order to further disclose the mechanisms of turbulence suppression and drag reduction,control and drag reduction in turbulence channel flow via normal and spanwise Lorentz force were investigated by direct numerical simulation (DNS) base on the standard Fourier-Chebyshev spectral method.The results show that for each λ⁺_x(the wavelength along the streamwise direction),there appears to be an optimal Lorentz force intensity St that is inversely proportional to λ⁺_x.The intrinsic flow structures are modified by the induced flow on application of the normal and spanwise Lorentz force control to the turbulent bundary layer. In the optimized parameter control,intrinsic and induced flows fields are modified each other when the normal and spanwise Lorentz force are utilized to modulate the near wall turbulence flow fields. As travelling with the normal and spanwise Lorentz force, the induced flow finally dominates the near-wall flow, leading to a reduction in turbulent drag of 8% approximately. 