Abstract
In this study, the effect of the aspect ratio on the aerodynamics characteristic of flexible membrane wings with different aspect ratios (AR = 1 and AR = 3) is experimentally investigated at Reynolds number of 25000. Time accurate measurements of membrane deformation using Digital Image Correlation system (DIC) is carried out while normal forces of the wing will be measured by helping a load-cell system and flow on the wing was visualized by means of smoke wire technic. The characteristics of high aspect ratio wings are shown to be affected by leading edge separation bubbles at low Reynolds number. It is concluded that the camber of membrane wing excites the separated shear layer and this situation increases the lift coefficient relatively more as compared to rigid wings. In membrane wings with low aspect ratio, unsteadiness included tip vortices and vortex shedding, and the combination of tip vortices and vortex shedding causes complex unsteady deformations of these membrane wings. The characteristic of high aspect ratio wings was shown to be affected by leading edge separation bubbles at low Reynolds numbers whereas the deformations of flexible wing with low aspect ratio affected by tip vortices and leading edge separation bubbles.
Highlights
Flexible membranes have been associated with a number of applications such as hang gliders, parachutes, paragliders, yacht sails, microlights, natural flyers such as bats and insects
The characteristics of high aspect ratio wings are shown to be affected by leading edge separation bubbles at low Reynolds number
The characteristic of high aspect ratio wings was shown to be affected by leading edge separation bubbles at low Reynolds numbers whereas the deformations of flexible wing with low aspect ratio affected by tip vortices and leading edge separation bubbles
Summary
Flexible membranes have been associated with a number of applications such as hang gliders, parachutes, paragliders, yacht sails, microlights, natural flyers such as bats and insects. Genç [4] investigated unsteady aerodynamics and flow-induced vibrations of a low aspect ratio rectangular membrane wing with excess length. They applied fluid-structure interaction method in the numerical simulation for the aerodynamic characteristics and response between flow field and structure of the segmented flexible airfoils They noticed that the segmented flexible airfoils carried out a higher maximum lift coefficient, and postponed the stall effectively. Attar et al [11] studied on experimental characterization of aerodynamic behaviours of membrane wings in low Reynolds number of Re = 13700, 22600 and 36300 and the angle of attack up to 27°. Dynamic results for the flexible models appeared large RMS values of lift and drag at the largest Reynolds number, which mostly reduced with increasing angle of attack. They observed hysteresis of the membrane airfoil near zero angle of attack experimentally
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