PPPL-4866
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 modication
of vortices in the wake of a circular cylinder with its axis parallel to the applied
magnetic field. 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 profiles as a
function of radius for vortices shed by the cylinder at varying strengths of magnetic field.
Results indicate a signicant change in vortex radius and rotation as N is increased.
The lack of deviations from the vortex velocity profile at high magnetic fields 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 modication of the small-scale eddies by the magnetic field. 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.
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Submitted to: Journal of Fluid Mechanics, Cambridge University Press (April 2013)
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Download PPPL-4866 (pdf2.7 MB 16 pp)
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