Rigid and Flexible Low Reynolds Number Airfoils

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Abstract
Issues related to the design of low Reynolds number airfoils, such as the thickness, camber, and surface profiles, are investigated. To contrast the issues involved, NACA 0012 and CLARK-Y, two well-known airfoils, a recently proposed low Reynolds number airfoil S1223, and a modified airfoil UF, are compared under varied Reynolds numbers and angles of attack. These airfoils range from 0% (NACA 0012) to 8.89% (S1223) camber, and from 6% (UF) to 12.9% (CLARK-Y) thickness, and allow us to make a broad comparison of the lift-and-drag characteristics with varying Reynolds numbers, from 7.5 × 104 to 2.0 × 106. Furthermore, the concept of a flexible airfoil is assessed in an unsteady, low Reynolds number environment. To facilitate the present study, we have employed techniques treating either inviscid or coupled inviscid/boundary-layer flows around rigid airfoils, as well as a moving boundary technique to handle an elastic, massless membrane in a portion of the upper airfoil surface. The results show that within the range of Reynolds numbers and airfoil shapes, increased camber and reduced thickness provide more favorable lift-and-drag characteristics when the Reynolds number becomes lower. The results also indicate that a flexible profile yields better overall performance than a similar rigid profile in an oscillating freestream