Document Type

Master's thesis

Date of Degree

2012

Degree Name

MS (Master of Science)

Department

Mechanical Engineering

First Advisor

James H. J. Buchholz

Abstract

The initial rotation of flat, rectangular plates in quiescent flow were studied experimentally using two-dimensional and stereoscopic particle image velocimetry. The study examined the vortex dynamics of spanwise vorticity created on the upper, leeward surface of each plate of aspect ratio 2 and 4, which consists primarily of a leading-edge vortex. Reynolds numbers of 4,000, 8,000, and 16,000 based on the tip velocity and angles of attack of 25°, 35°, and 45° were investigated at five different azimuthal locations (90°, 180°, 235°, 270°, and 320°). The 25% and 50% spanwise positions for the aspect ratio 4 plate and 50% spanwise position for the aspect ratio 2 plate were studied. For the 25% and 50% spanwise location for the aspect ratio 4 and 2 plate, respectively, the leading-edge vortex structure's shape and coherence appear to be evolving temporally as the plate begins its initial motion. Leading-edge vortex circulation measurements confirm there is a non-monotonic trend showing increasing values until an azimuthal position of approximately 220° where there is a dip in the circulation values, but the circulation then rises towards the end of the range of azimuthal positions investigated. A strong region of counter-rotating vorticity was observed on the surface of the plate beneath the leading-edge vortex from the interaction of the leading-edge vortex with the plate. It was hypothesized that the interactions between the leading-edge vortex and counter-rotating vorticity are an important factor in governing the dynamics and strength of the leading-edge vortex which may ultimately determine whether the leading-edge vortex remains attached. To validate this claim, a transport analysis of the vorticity in the leading-edge vortex was developed to determine the contributions of spanwise flux, tilting of in-plane vorticity components, the shear layer, and annihilation has on the rate of change of circulation of the leading-edge vortex in the spanwise direction. Results of this analysis indicate that annihilation of the leading-edge vortex from entrainment of the counter-rotating vorticity is an important factor in governing the dynamics of the leading-edge vortex.

Pages

xviii, 200

Bibliography

191-200

Comments

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Copyright

Copyright 2012 Craig James Wojcik