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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λx+,存在最佳的电磁力强度St,使阻力降最大,最佳St与λx+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%。
The normal and extensional electromagnetic forces can effectively modulate turbulent flow near the wall and reduce the frictional resistance of the wall. In order to further reveal the drag reduction mechanism of the method, the control of normal and forward electromagnetic force and the drag reduction of the turbulent channel were studied by using the Fourier-Chebyshev spectral method through direct numerical simulation (DNS). The results show that for the given wavelength λx +, there exists the best electromagnetic force St, which makes the resistance drop maximum and the optimal St is inversely proportional to λx +. The control of turbulence by electromagnetic force in the normal and extensional processes is essentially a modulation of wall turbulence induced by electromagnetic force. Under the control of optimization parameters, both the normal flow field and the induced flow field are modulated at the same time when the flow field induced by the electromagnetic force in the normal direction and the spread direction is used to modulate the inherent near-wall turbulent flow field. Under this modulation wave, the modulated flow field gradually dominates the boundary layer of the wall, which leads to the decrease of the wall resistance with the average drag reduction rate of up to 8%.