Roll stall and the vortex-induced aerodynamic of low-aspect-ratio fliers

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The design and development of highly-maneuverable aircraft has been a long-standing engineering challenge. This challenge presents itself in almost all flight regimes, from supersonic fighter jets down to low-speed, smaller-scale unmanned aircraft. Despite the very different operating conditions, there is at least one common feature among aircraft designs aiming to provide very agile, yet stable, flight. Namely, the planforms (the shape and layout of an airplane's wing) of such aircraft are of low aspect ratio. Recent studies suggest that the aerodynamic and gust-response of such low aspect ratio fliers are significantly different than larger flyers and not well understood. This issue constitutes a critical gap in aerial vehicle development, and this research project addresses a critical gap in the development of reliable and fully controllable aerial drones. The researchers will also enhance course curricula with results from this research, and a course on unsteady low Reynolds number aerodynamics will be developed. A summer program is proposed that will enable local high school students to learn aerodynamics and flight concepts and to participate in a design/build/operate competition integrating fluid dynamics, aerodynamics, and aircraft design. This research project takes a fresh look into new features of steady and unsteady aerodynamics of low aspect ratio wings. Recent discoveries of complex aerodynamic flow-structure interactions have been attributed to an inherent coupling of lateral and longitude loadings and these are unique to low aspect ratio flyers. These phenomena are, in turn, related to the vortex-dominated flow generated by such wings. The proposed work is divided into three main research thrusts. (i) The prediction of flow separation, (ii) The connection between unsteady vortex generation of low-aspect-ratio surfaces and the instantaneous loadings, and (iii) Understanding of how key changes to the vortex topology over a wing in cross-flow modify the asymmetric wing loading. Flow field measurements using digital particle image velocimetry and direct force/moment measurements are correlated with the vortex structures in the flow. Some theoretical modeling will also complement the experimental effort. This knowledge may motivate unique flow control or wing morphing strategies during flight in gusty environments.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.