Decoupled Effects of Localized Camber and Spanwise Bending for Flexible Thin Wing

Abstract

Investigated and revealed are new insights into the individual, decoupled effects of induced camber and spanwise bending on the lift, drag, and endurance for an optimum flexibility membrane-and-frame wing at Reynolds number 80,000. While previous studies into thin, flexible-wing designs for fixed-wing unmanned aerial vehicles have been shown to improve aerodynamic performance and delay the onset of stall, the individual contributions of localized induced camber and spanwise bending on the performance improvement have not been sufficiently examined. Furthermore, since the locally induced camber and spanwise bending generally occur simultaneously, their decoupled effects are not well understood. This Paper first introduces a wing frame optimization approach using a rapid fluid/structure interaction model to identify a wing flexibility design that maximizes aerodynamic endurance. A higher-fidelity, large-eddy simulation is then used for validation of the optimized wing flexibility and to help explain both the coupled and uncoupled effects of the induced camber and spanwise bending that contribute to maximum performance. The formation of several locally induced cambers at specific planform regions is found to create greater endurance (minimum power required) through favorable lift generation, in addition to reduced drag at relatively high angles of attack. Spanwise bending, however, is observed to be a noncontributing byproduct of the increased thin-wing flexibility. Detailed pressure distributions and instantaneous flow structure visualizations from large-eddy simulation provide new insights into the individual contributions of induced camber and spanwise bending while also justifying the optimum wing design.