On the application of active open-loop and closed-loop controls on a circular cylinder in the presence and absence of a free surface

Reid, Gina S. (2010) On the application of active open-loop and closed-loop controls on a circular cylinder in the presence and absence of a free surface. Masters thesis, Memorial University of Newfoundland.

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Abstract

This thesis focuses on the application of active open-loop and closed-loop controls on a circular cylinder in the presence and absence of a free surface. The numerical simulations are presented for two-dimensional, uniform, flow of a viscous incompressible fluid past a circular cylinder subject to forced (i) transverse or streamwise oscillations, or (ii) combined streamwise and transverse oscillations, which to the author's knowledge has not previously been studied. The goal of this thesis is to analyze in detail the effects of these three types of cylinder oscillations, and the inclusion of a free-surface on the vortex shedding modes in the near wake region, fluid forces acting on the cylinder as well as pressure distribution around the cylinder. -- The numerical method of the study is based on the finite-volume discretization of the special integral form of two-dimensional continuity and unsteady Navier-Stokes equations (when a solid body is present) based on a two-fluid model. The numerical simulations are conducted at a Reynolds number of R = 200, for the Froude numbers Fr ≈ 0.0, Fr = 0.2 and 0.4, at three different cylinder submergence depths, h = 0.25, 0.5 and 0.75. The flow characteristics are examined for a maximum oscillation amplitude A = 0.13, and forcing cylinder oscillation frequency-to-natural vortex shedding frequency ratios ƒ /ƒₒ = 1.25,1.75,2.25,2.75. The numerical simulations are carried out using the computational fluid dynamics code developed by Dr. Kocabiyik's research group at Memorial University. -- The results detail the link between the lift force, equivorticity patterns and the pressure fields which was previously uncharted, and paves the way for understanding the application of active flow control mechanisms on coastal and offshore engineering systems.

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