Computations of the harmonically forced, unsteady viscous flow over a flexible, two-dimensional membrane wing are presented. The aeroelastic problem is nondimensionalized and a set of six basic dimensionless parameters is derived which govern the physical problem. An additional parameter, the frequency ratio, is proposed as a meaningful parameter for characterizing the harmonically driven unsteady problem. The investigation is facilitated by distinguishing three distinct classes of problems - the constant tension, elastic and inextensible membrane problems - which are associated with limiting cases of the dimensionless parameter set. A pressure-based method for the incompressible Navier-Stokes equations written in general time dependent curvilinear coordinates is adopted as the flow solver. The computations are limited to Reynolds numbers near the upper limit of the laminar flow regime. Ostensibly, the computations are designed to simulate the behavior of a marine sail in a wind gust; however, the simulation of a harmonically forced freestream flow also proves to be a useful vehicle for demonstrating some of the more generic features of membrane wing mechanics. The periodic appearance and collapse of recirculation zones, along with an attendant adjustment in membrane configuration, results in an aeroelastic response which may not be characterized as simple harmonic response at the freestream forcing frequency.
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