Abstract
In this study, unsteady flow around flexible membrane wing which had aspect ratio of 1 (AR=1) was investigated experimentally at various Reynolds numbers (Re = 25000 and Re = 50000). Smoke-wire technique for flow visualization over the flexible membrane wing was utilized in the experiments. Digital Image Correlation system (DIC) was used for measuring deformation of AR = 1 flexible membrane wing. Instantaneous deformation measurements of membrane wing were combined with the flow field measurements. In low aspect ratio flexible membrane wings, unsteadiness includes tip vortices and vortex shedding, and the combination of tip vortices. In these types of wings, complex unsteady deformations occurred due to vortex shedding. The results showed that the increasing angle of attack results in increase of membrane deformation. Moreover, it was concluded that analysis of the instantaneous deformation revealed chordwise and spanwise, modes which were due to the shedding of leading-edge vortices as well as tip vortices. Consequently, vibrational mode decreased and maximum standard deviation location approached to the trailing edge by reason of increasing angle of attack.
Highlights
Vibrational mode decreased and maximum standard deviation location approached to the trailing edge by reason of increasing angle of attack
Due to the advances in unmanned aerial vehicles (UAV), micro air vehicles (MAV) and wind turbines, aerodynamics researches concentrated on low Reynolds number aerodynamics, transition and laminar separation bubble (LSB) and its effects on aerodynamic performance [1,2,3,4,5]
Membrane wings are used in many engineering applications such as microlight, yacht sails, parachutes, hang glider wings, paraglider and wings of small unmanned air vehicles go by the name of micro air vehicles (MAVs) [6]
Summary
Due to the advances in unmanned aerial vehicles (UAV), micro air vehicles (MAV) and wind turbines, aerodynamics researches concentrated on low Reynolds number aerodynamics, transition and laminar separation bubble (LSB) and its effects on aerodynamic performance [1,2,3,4,5]. Rojratsirikul et al [8] investigated two dimensional flexible membrane airfoils experimentally with respect to the effects of membrane pre-strain and excess length on unsteady fluid structure interactions of membrane airfoils The largest camber and strain were observed for the airfoil with excess length They noticed that the onset of the membrane airfoil vibrations was postponed to a higher angle of attack for the airfoils with excess length. Kuo and Hsieh [15] studied on unsteady flow structure and vorticity convection over NACA0012 airfoil oscillating at high reduced frequency They noticed that the leading edge separation vortices were combined one by one into a vortex near the trailing edge and shed together downstream into the wake. Decrease in aspect ratio caused to increasing of plate drag coefficient
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