An Experimental Study of Flexible Membrane Airfoils at Low Reynolds Numbers

Abstract

An experimental study was conducted to explore the benefits of using flexible membrane airfoils/wings at low Reynolds numbers for MAV applications. In addition to measuring aerodynamic forces acting on the flexible membrane airfoils/wings, a high-resolution Particle Image Velocimetry (PIV) system was used to conduct flow field measurements to quantify the transient behavior of vortex and turbulent flow structures around the flexible membrane airfoils/wings at different angles of attack. The force measurement results revealed that flexible membrane airfoils can provide better aerodynamic performance compared with their rigid counterpart at low Reynolds numbers. The flexibility (or rigidity) of the membrane skins was found to affect the aerodynamic performance of the membrane airfoils significantly. The PIV measurements elucidated that flexible membrane airfoils changed their camber (i.e., cross sectional shape) automatically to adapt incoming flows to balance the pressure differences applied on the upper and lower surfaces of the airfoils at different angles of attack, thereby suppressing flow separation on the membrane airfoils. The deformation of the flexible membrane airfoils also reduced the effective angle of attack of the airfoils to delay airfoil stall.