Unsteady spatially varying flow control: I. 'Void' structure in the wake of a self-oscillating flexible cylinder. II. Design of a backward-facing step control device

This thesis concerns unsteady flow control in two different flow geometries. The first is an experimental study involving the discovery of a new large scale vortex "void" structure in the wake of cylinder undergoing vortex induced vibration that includes vortex pinch-off. We simulated the vibration of this cylinder from measurements of shedding frequency and cylinder tension. The structure's span-wise location is correlated with an anti-node in the transverse vibration and a node in the stream-wise vibration. Hydrogen bubble flow visualization is shown to be well suited for cylinder research, as the bubbles directly visualize the vortex structure when they become trapped in the low pressure cores of the vortex street. Bubbles do not affect well known cylinder shedding and vibration characteristics. The second flow geometry involves the design and construction of a backward-facing step flow control device which, in addition to all other desirable characteristics, is capable of span-wise varying actuation not previously studied experimentally.