Flexibility effects on vortex formation of translating plates

Abstract

Vortex structures made by impulsively translating low aspect-ratio plates are studied experimentally using defocusing digital particle image velocimetry. The investigation of translating plates with a 90• angle of attack is important since it is a fundamental model for a better understanding of drag-based propulsion systems. Rectangular flatrigid, flexible and curved-rigid thin plates with the same aspect ratio are studied in order to develop qualitative and quantitative understanding of their vortex structures and hydrodynamic forces. We find that the vortex formation processes of all three cases are drastically different from each other. The interaction of leading-edge vortices and tip flow near the tip region is an important mechanism to distinguish vortex patterns among these three cases. The drag trends of three cases are correlated closely with vortex structure and circulation. The initial peak of hydrodynamic force in the flexible plate case is not as large as the initial peak of the flat and curved rigid plate cases during the acceleration phase. However, after the initial peak, the flexible plate generates a large force comparable to that of the flat-rigid plate case in spite of its deformed shape, which results from the slow development of the vortex structure.

Vorticity transport in the leading-edge vortex on a rotating blade

“…Local analyses of vorticity transport in the leading-edge vortex To understand the relative importance of local mechanisms of vorticity transport in the leading-edge vortex, a more detailed control volume analysis was developed, bearing some similarity to that of Kim & Gharib (2011), and conducted on the planar control volume illustrated in figure 3, at b/s = 0.25 and 0.50. The control volume is again bounded by a vorticity isocontour of −20 s −1 and the line L y as shown in figure 3.…”

Investigation of vortex development on accelerating spanwise-flexible wings

“…Therefore the stability of such LEVs is crucial for high-lift production at low Reynolds numbers. Although the mechanism of LEV stability is not understood, Kim and Gharib (2011) identified delayed LEV detachment for spanwise flexible profiles in the presence of a free tip. In order to gain an understanding of LEV development with respect to flexible wings, a hypothesis regarding how a phase-delay in effective flow velocity could affect the LEV growth along the span is derived.…”

Lift generation with optimal elastic pitching for a flapping plate

“…Ramananarivo, Godoy-Diana & Thiria (2011) assumed inertia to be the dominating force in passive pitching, and showed that the interplay between heaving-pitching phase difference and aerodynamics has a key role in propulsive efficiency. Kim & Gharib (2011) linked the increase in the forces acting on a flexible plate to the delayed development of three-dimensional vortex formation. Khan, Steelman & Agrawal (2009) approached the passive pitching mechanism from a design perspective, by optimizing a set of nonlinear spring parameters to maximize the lift based on a quasi-unsteady model.…”