Impact of compliance on propulsive efficiency in two dimensional flapping

Dean E Bryson, Purdue University

Abstract

Micro air vehicles are an emerging class of portable unmanned aerial systems designed to be easily deployed in close-quarters environments. They operate in a flight regime where flapping wings can leverage unsteady aerodynamic mechanisms to enhance force production. The impact of inherent structural flexibility on flapping micro air vehicle performance must be determined. A new, geometrically nonlinear aeroelastic simulation capability was developed for the study of forward flapping flight in two dimensions. A structural dynamics model was adapted from the classical pitch-and-plunge aeroelastic model, and features flexibility between the wing section and the point where flapping motion is applied. The structure was coupled with a vortex particle aerodynamics method that models the unsteady wake and includes the effect of apparent mass from the fluid surrounding the flapping wing. A series of parametric studies were performed for a forward flight condition using pitch, plunge, and fore-and-aft stiffness coeffcients as design variables and propulsive effciency as a performance metric. The studies used ten different combinations of pitch offset angle, pitch-plunge forcing phase angle, forward velocity, and inclusion or neglect of aerodynamic forces in solving the equations of motion. The results of the studies demonstrate that aeroelastic coupling is critical to the flexible response of flapping wings, the phase relationships of the flexible response drive the thrust production as well as the power required for flapping, flapping the system at its natural frequency does not give peak propulsive effciency, and both structural dynamics along with aerodynamics must be considered simultaneously to find the overall peak performance.

Degree

M.S.A.A.

Advisors

Weisshaar, Purdue University.

Subject Area

Mechanics|Aerospace engineering

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