Fluid-Structure Interaction of Oscillating Low Aspect Ratio Wings at Low Reynolds Numbers
Abstract
Detailed force measurements on a plunging rectangular wing with semi aspect ratio of 2, at low Reynolds numbers of 10,000-30,000 have been conducted in a water tunnel at various non-dimensional frequencies and amplitudes, alongside particle image velocimetry (PIV) measurements of the flow at the midspan plane and hot film measurements in the wake. The presence of multiple peaks in lift has been identified for this three-dimensional wing, thought to be related to the natural shedding frequency of the stationary wing. Wing/vortex and vortex/vortex interactions have been identified which may also contribute to the selection of optimal frequencies. Lift enhancement is observed to become more notable with increasing amplitude, coupled with a slight shift in the peak frequencies, to lower Strouhal numbers, with 3 increasing angle of attack. Despite the highly three-dimensional nature of the flow, lift enhancements up to 180% are possible. The unsteady aerodynamics of low aspect ratio membrane wings (rectangular wing and delta wing) has been investigated in a Reynolds number range of 24,000 - 59,000. Membrane deformations were measured by using a Digital Image Correlation (DIC) system. Force measurements were conducted for membrane wings and compared with those of rigid wings of similar geometries. The comparison indicates that the effect of flexibility benefits the rectangular wing more than the delta wing by increasing the maximum normal force as well as the slope by a larger amount. Oscillations of the membrane, mode shapes, and the corresponding vibration frequencies were investigated. The combination of tip vortices and leading-edge vortex shedding results in a mixture of streamwise and spanwise vibrational modes. The Strouhal numbers of membrane vibration frequencies are on the order of unity, and have similar range to those of two-dimensional airfoils.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 2010
- Accession Number
- ADA530867
Entities
People
- Zhijin Wang
Organizations
- University of Bath