While a wide variety of active flow control techniques have been developed for rigid wings, membrane wings have generally relied on their inherent passive deformation to flow conditions. But as micro-air vehicles (MAVs) become more prevalent, the benefits of membrane wings at low Reynolds number make the development of novel control and sensing techniques particularly relevant. In this work, the foundation is laid for an integrated sensing and control system, in which a membrane wing is constructed from a dielectric elastomer actuator. The membrane material, VHB 4905 (3M), is characterized using a three-element generalized Kelvin-Voigt model, which is fitted to experimental data for creep, relaxation, and steady state AC actuation. The performance of a fixed membrane wing under sinusoidal actuation is demonstrated for a range of angles of attack, freestream velocities, and actuation frequencies. Enhancements in the coefficient of lift of up to 20\% are seen within a limited range of experimental parameters. In this regime, actuation is seen to cause or enhance vortex shedding from the leading edge, as visualized with DMD analysis. The root cause of this peak in performance is explored, including the effects of reduced frequency, the location of the separated shear layer, and fluid-induced damping. Finally, integrated self-sensing of the membrane wing is demonstrated. The deformation of the membrane is sensed using the capacitance of the wing, which is measured using an online RLS algorithm. The parameters of the algorithm are optimized, and the performance is validated in a series of benchtop and wind tunnel tests. The correlation between camber and aerodynamic load is demonstrated, and the unsteady camber is linked to large-scale structures in the surrounding flow. Ultimately, the combination of active flow control and integrated sensing may allow the development of closed-loop control of membrane wings, enhancing the capabilities of MAVs.
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Citation
Bohnker, Jillian,
"Sensing and Control of Flows over Membrane Wings"
(2019).
Engineering Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.26300/7160-aa38
