Date of Thesis

Summer 2018

Thesis Type

Masters Thesis

Degree Type

Master of Science in Mechanical Engineering

Major

Mechanical Engineering

First Advisor

Charles Knisely

Second Advisor

Andrew Sloboda

Third Advisor

Laura Beninati

Keywords

Dynamics, cylinder, vibration, vortex shedding, wall proximity

Abstract

The effect of wall proximity on the mechanism of flow-induced vibration of a circular cylinder mounted in a wind tunnel and free to vibrate with two degrees-of-freedom near a rigid plane boundary were examined at a Reynolds number of 1.86 x 105. Hot-wire anemometry and cylinder-mounted accelerometers were used to characterize the flow-induced vibration of the cylinder. In the near wall region (gap ratios, G/D< 0.4) the system was found to exhibit symptoms of movement-induced vibration resulting from the push-and-draw effect of the cylinder pushing into and out of the fluid immediately upstream and downstream of the cylinder. The variation of the width of the separated wake region with the cylinder motion produces a force in phase with the cylinder velocity, resulting in excitation of the cylinder motion. For G/D > 1.0, the alternate shedding of vortices (the Kármán vortex street) produces a fluctuating lift on the body. The lift force also has an associated drag fluctuation at twice the vortex shedding frequency For 0.4 > G/D> 1.0, the excitation appears to be due to the combined effects of the movement-induced vibration found in the near wall region with the vortex shedding from the cylinder found for the free cylinder when it is far from the wall.. The system exhibited mechanical coupling of the two degrees-of-freedom, so additional tests will be needed to conclusively confirm the findings presented in this thesis.

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