Vortex formation and saturation for low-aspect-ratio rotating flat-plate fins |
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Authors: | Adam?C?DeVoria Email author" target="_blank">Matthew?J?RinguetteEmail author |
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Institution: | (1) State University of New York at Buffalo, 318 Jarvis Hall, Buffalo, NY 14260, USA; |
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Abstract: | We investigate experimentally the unsteady, three-dimensional vortex formation of low-aspect-ratio, trapezoidal flat-plate
fins undergoing rotation from rest at a 90° angle of attack and Reynolds numbers of O(103). The objectives are to characterize the unsteady three-dimensional vortex structure, examine vortex saturation, and understand
the effects of the root-to-tip flow for different velocity programs. The experiments are conducted in a water tank facility,
and the diagnostic tools are dye flow visualization and digital particle image velocimetry. The dye visualizations show that
the low-aspect-ratio plate produces symmetric ring-like vortices comprised mainly of tip-edge vorticity. They also indicate
the presence of the root-to-tip velocity. For large rotational amplitudes, the primary ring-like vortex sheds and a secondary
ring-like vortex is generated while the plate is still in motion, indicating saturation of the leading vortex. The time-varying
vortex circulation in the flow symmetry plane provides quantitative evidence of vortex saturation. The phenomenon of saturation
is observed for several plate velocity programs. The temporal development of the vortex circulation is often complex, which
prevents an objective determination of an exact saturation time. This is the result of an interaction between the developing
vortex and the root-to-tip flow, which breaks apart the vortex. However, it is possible to define a range of time during which
the vortex reaches saturation. A formation-parameter definition is investigated and is found to reasonably predict the state
corresponding to the pinch-off of the initial tip vortex across the velocity programs tested. This event is the lower bound
on the saturation time range. |
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