The near cylinder time-varying flowfields associated with transverse lift forces are measured in a reversing planar flow. A new technique that uses the phase angle of the fundamental harmonic of the lift force to identify flowfield changes due to intermittent shedding and switching of vortices from one shoulder of the cylinder to the other is presented. The measurements reveal the development of vortex structures around the cylinder for several stages of flow-mode discriminated oscillation cycles.
The experiments were conducted in a unique hydrodynamic tunnel facility which combines a computer- controlled laser velocimetry probe and a high-sensitivity multi-axis load cell for accurately measuring simultaneous streamwise, cross-stream water velocities, inline and lift forces, and moments of a cylinder mounted in the manner of a cantilever in Reynolds number flows up to 25,000 and Keulegan-Carpenter numbers up to 20.
The data analysis uncovers physical insights of the relationship between lift force and the local flow structures that are important for development of theoretically sound wave force models. For instance, in the present work, a lift force model-equation, built upon measured flow circulation and added-mass concepts, has been developed and shown to perform very well compared to measurements and works of previous investigators.
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