An Euler–Lagrangian hybrid method for the evolution of near-wall coherent structures with the effect of electromagnetic force

In this paper, the turbulent channel flow field is calculated with the direct numerical simulation method at Re = 4000. Based on the Eulerian–Lagrangian framework, the identification and spatiotemporal evolution analysis of Lagrangian coherent structures in turbulence are achieved by combining the Finite Time Lyapunov Exponent and the instantaneous vortex identification criterion (λci) derived from the eigenvalues of the velocity gradient tensor. The results demonstrate that the generation, development, and decay processes of quasi-streamwise vortices, along with their coupling interaction with streaks, significantly alter the near-wall fluid ejection and sweeping processes, thereby modifying the wall shear stress and its distribution. Meanwhile, the oscillating electromagnetic force induces a Stokes layer in the flow field, acting on the quasi-streamwise vortices and causing their distortion and deformation during the generation and development stages. It is revealed that the action suppresses the intensity of turbulent bursts and enhances dissipation during the decay of streamwise vortices, ultimately altering the distribution of the local wall shear stress and significantly reducing the wall shear stress.