Vortical structures and turbulent bursts behind magnetic obstacles in transitional flow regimes

摘要

The present paper reports on numerical investigations of vortical structures in transient flow regimes generated by the local action of the Lorentz force on an electrically conductive fluid. The locally imposed non-uniform magnetic field generates similar effects as observed for flows over submerged solid obstacles. It is demonstrated that complex flow patterns can be generated by imposing magnetic fields of different strengths. The initial validation of the electromagnetically extended Navier-Stokes solver on unstructured numerical grids is performed in the low-Reynolds number range 100 ≤ Re ≤ 400 for different values of the magnetic interaction parameter. A generally good agreement is obtained in comparison with similar numerical studies of Votyakov et al. (2007,2008) for the low-Reynolds number cases. Then, a series of simulations are performed in transitional flow regimes (Re = 900) for different values of the interaction parameter (N = 3,...,25). Simulations demonstrated the appearance of vortex-shedding phenomena similar to the flows behind solid obstacles. In contrast to the solid obstacles, the magnetic obstacles also generated the vortical flow patterns inside the magnetically affected regions. This feature can be used for the flow control of electrically conductive fluids, for efficient enhancements of the wall-heat transfer or for better mixing of passive scalars. Despite the laminar inflow conditions, turbulent bursts are observed in the magnetic wake region for the Re = 900 case. The velocity spectra and spatial distributions of the long-time averaged second-moments of the velocity field demonstrated that turbulence was locally sustained in the proximity of the magnetic wake edge.