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Rotation of a Pulsed Jet in a Rotating Annulus:
A Source of Helicity for an α ω Dynamo
Howard F. Beckley
Department of Physics, New Mexico Institute of
Mining and Technology, Socorro, New Mexico 87801
Stirling A. Colgate
Theoretical Astrophysics Group, T6, Los Alamos
National Laboratory, Los Alamos, New Mexico 87545
Department of Physics, New Mexico Institute of
Mining and Technology, Socorro, New Mexico 87801
Van D. Romero
Vice President, R&ED, New Mexico Institute of
Mining and Technology, Socorro, New Mexico 87801
Department of Physics, New Mexico Institute of
Mining and Technology, Socorro, New Mexico 87801
Ragnar Ferrel
Department of Physics, New Mexico Institute of
Mining and Technology, Socorro, New Mexico 87801
Abstract
A hydrodynamic flow visualization experiment was
performed in water to investigate how an expanding pulsed jet rotates
when injected off-axis into a rotating annular flow field. In the
experiment the pulsed jets were injected parallel to, but radially
displaced from the axis of rotation. The jets were observed to
counter-rotate ΔΦ ~ π/2 to π radians
relative to the rotating frame before dispersing into the background
flow because of turbulence. The counter-rotation of the jet is
produced by the change in moment of inertia with conserved angular
momentum, or equivalently, the partial conservation of circulation due
to radial divergence of the flow at the head of the jet. Rapid
turbulent entrainment of the pulsed jet flow with the background flow
during radial divergence limits the net rotation of the jet, whereas
shear within a differentially-rotating background flow enhances the
net rotation of the jet. The Reynolds number of the experiment was
≅ 105 in order to simulate the behavior of turbulent
entrainment at high Reynolds number. The differential rotation of the
background flow was varied from constant rotation, dΩ/dR = 0,to Ω ∝ 1/R. The flow was visualized by pulsed hydrogen
electrolysis from a tungsten wire and dispersed guanidine in
water. The flow was imaged using a digital video camcorder operating
at 30 Hz frame rate. This hydrodynamic flow visualization experiment
is a precursor to the design and development of an α - Ω dynamo experiment using liquid sodium.
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