Direct numerical simulation analysis of spanwise oscillating Lorentz force in turbulent channel flow at low Reynolds number

Journal article, 2017

Direct numerical simulations of a turbulent channel flow at low Reynolds number ($Re_{\tau} = 180$, based on the driving pressure gradient and channel half width) are performed. Some results are also presented for $Re_{\tau} = 400$. In this work we apply an idealized spanwise Lorentz force near the lower wall of the channel and compared the results for the applied force and no-force cases in both the upper half and the lower half of the channel. We have studied two-point correlations to explain the effect of the Lorentz force on streamwise vortices and streaky structures. Despite the observation of the clear stabilization of the streaky structures in the vicinity of the wall, the existence of the streamwise vortices is explained by the well-known turbulence regeneration cycle, which improves the understanding of streaky and streamwise vortex structure formation on turbulence generation. Spanwise oscillating Lorentz force effects on the Rankine vortex structures are investigated. Our results lead us to establish an explanation on the effect of sweep and ejection events on the mean vortex structures in the flow field. A mean vortex structure is defined by the time-averaged location of the local minimum and maximum of the streamwise r.m.s. vorticity. We also depict turbulence production rates for both cases and compared the lower and upper half of the channel.