Effects of Magnetic Field on the Turbulent Wake of a Cylinder in MHD Channel Flow
Authors: John Rhoads, Eric Edlund and Hantao Ji
Abstract:
Results from a free-surface MHD flow experiment are presented detailing the modi cation
of vortices in the wake of a circular cylinder with its axis parallel to the applied
magnetic fi eld. Experiments were performed with a Reynolds number near Re ~ 104 as
the interaction parameter, N = |j x B| / |ρ (υ ⋅ ∇), was increased through unity. By
concurrently sampling the downstream fluid velocity at sixteen cross-stream locations
in the wake, it was possible to extract an ensemble of azimuthal velocity profi les as a
function of radius for vortices shed by the cylinder at varying strengths of magnetic field.
Results indicate a signi cant change in vortex radius and rotation as N is increased.
The lack of deviations from the vortex velocity pro file at high magnetic fi elds suggests
the absence of small-scale turbulent features. By sampling the wake at three locations
downstream in subsequent experiments, the decay of the vortices was examined and the
effective viscosity was found to decrease as N-049±0.4. This reduction in effective viscosity
is due to the modi cation of the small-scale eddies by the magnetic fi eld. The slope of
the energy spectrum was observed to change from a k-1.8 power-law at low N to a k-3.5
power-law for N > 1. Together, these results suggest the flow smoothly transitioned to
a quasi-two-dimensional state in the range 0 < N < 1.
__________________________________________________
Submitted to: Journal of Fluid Mechanics, Cambridge University Press (April 2013)
__________________________________________________
Download PPPL-4866 (pdf2.7 MB 16 pp)
__________________________________________________