Covert-Inspired Deployable Structures for Separation Control and Gust Alleviation

An image of an airfoil simulated with covert-inspired flaps

Proposed prototype to investigate the effects of changing material properties and spring constants. In this prototype, each rib in the wing supports a number of movable panels that deploy under specific conditions. Each flap is attached to a torsion spring.

Nature’s Inspiration

Unmanned aerial vehicles are expected to fulfill increasingly complex mission requirements but are limited by their inability to efficiently perform high-angle-of-attack maneuvers at low Reynolds numbers, while birds seem to perform these maneuvers with little effort. Birds use a passively-deployed feather called the covert feather to correct for flow reversal over their wings during high-angle-of-attack maneuvers, thereby delaying the onset of stall.

Coverts

BAM Approach

Currently, an aeroelastic model is being developed that will guide the design process for the covert-inspired deployable structures. A preliminary model has been used to determine the hinge stiffness and mass of a single covert-inspired flap attached to the upper surface of an airfoil.

Wind tunnel test

Wind tunnel tests were conducted to investigate how the lift was affected by the presence of a flap at different chord-wise locations along the suction side of an airfoil. The wind tunnel test set up is shown as below:

Some primary result showed that the flap can increase maximum lift coefficient, as shown below:

CFD validation

Detached Eddy Simulation (DES) were conducted using ANSYS Fluent. These simulations were used to determine the effect of the flap on the flow field and pressure coefficient. An airfoil at angles of attack of 18 deg were tested with and without a flap.

Publications

Duan, C. and A. Wissa. “Covert-Inspired Flaps: Studying the Effects of Reynolds Number and Airfoil Geometry,” AIAA Journal (Under Review)
Wissa, Aimy, Chengfang Duan, and Mihary Ito. "Avian-Inspired Devices for Improved Mission Adaptability in Unmanned Aerial Vehicles." APS 2019 (2019): S64-009.
Duan, C., J. Waite, and A. Wissa. "Design Optimization of a Covert Feather-Inspired Deployable Structure for Increased Lift", 2018 Applied Aerodynamics Conference, AIAA AVIATION Forum, AIAA 2018-3174, Atlanta GA (Extended abstract was subject to peer review)
Waite, J., C. Duan, G. Reich, and A. Wissa "Computational Model for Application of Avian Covert Feathers to Aerial Vehicles," International Conference of Adaptive Structures and Technologies 2016, Bolton Landing, NY.

Acknowledgement

This work was funded by the the Air Force Research Laboratory Summer Faculty Fellowship program, and AFOSR YIP Award # FA9550-18-1-0298 (PM: Dr. Jaime Tiley).