Rigid and Flexible Low Reynolds Number Airfoils

Abstract

Issues related to the design of low Reynolds number airfoils, such as the thickness, camber, and surface proe les, 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 modie ed airfoil UF, are compared under varied Reynolds numbers and angles of attack. These airfoilsrange from 0% (NACA 0012)to 8.89%(S1223)camber, and from 6% (UF)to12.9%(CLARK-Y)thickness,and allowusto makea broadcomparison of thelift-and-drag characteristics with varying Reynolds numbers, from 7.5 £ 104 to 2.0 £ 106. Furthermore, the concept of a e exible 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 e ows 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 e exible proe le yields better overall performance than a similar rigid proe le in an oscillating freestream.