Turbulent drag reduction via a transverse wave traveling along streamwise direction induced by Lorentz force

Lorentz force can be used to induce motion in the electrically conducting fluids which might then lead to turbulence suppression and drag reduction. In this paper, drag reduction in turbulent channel flow via a transverse wave traveling along streamwise direction induced by Lorentz force is investigated numerically by direct numerical simulation. It is found that the intrinsic and induced flows are modified each other due to the two-way coupling when the transverse wavy Lorentz force is utilized to modulate the near-wall turbulent flow. There is an optimal wave number k(x) in flow control, in which the influence of the intrinsic flow on the induced flow is weakest, and on the contrary, the intrinsic turbulent flow is modified strongly by the induced flow. The variable-interval space averaging detective technique (a spatial version of the VITA technique) and conditionally sampled and ensemble averaging method are used to obtain the frequency and intensity of the turbulent bursts which mainly contribute to the turbulent skin-friction drag. The results show that the frequency and intensity vary with k(x) in the contradictious tendencies. Therefore, the turbulent skin-friction reduction can be optimized with k(x). It is also shown that the maximum drag reduction is affected by the oscillation parameters.