Theoretical investigation of the aerodynamics of double membrane sailwing airfoil sections

Abstract

The type of sailwing here investigated has a rigid leading-edge spar with a rib at each end, a wire trailing-edge, and membranes which are wrapped around this structure to form upper and lower wing-surfaces. There appears to have been no previous theoretical investigation of a sailwing of this type, although it is expected to have aerodynamic and structural advantages, including controllability by using internal pressure, and to have various applications (e.g. wind-driven generators). Previous theoretical investigations of sailwings have concerned wings with a zero-thickness single membrane. The paper presents a two-dimensional numerical analysis method for obtaining the aerodynamic characteristics of such double-membrane sailwings. Numerical examples are given which show that: i) the pressure distribution on a sailwing with a rounded leading-edge is completely different from that on a single-membrane sailwing. ii) A sailwing with a circular or oval leading-edge has sharp suction peaks in the pressure distribution that may impair performance. iii) A D-spar leading-edge sailwing shows a large improvement in respect of pressure peaks; this is in qualitative agreement with the performance improvement noted in earlier experiments elsewhere with this form of leading edge. See next Abstract.