Characterizing the effect of airfoil geometry on extreme aerodynamic events

Extreme aerodynamic effects pose a significant challenge for the regular operations of small-scale aerial vehicles, as they introduce large perturbations that can compromise stability and reduce performance. Through this research, we seek to understand the influence of the airfoil geometry on the magnitude and nature of the nonlinear effects on extreme aerodynamic flows, in this case represented by vortex gusts. We conduct a systematic analysis based on an extensive dataset comprised of several configurations including 4-digit NACA profiles fixed at several angles of attack, subject to vortex-gusts of a range of sizes, strengths and vertical initial positions, simulated at a chord-based Re=100 using an immersed boundary method. We examine both the evolution of the aerodynamic loads and flow fields, and we exploit the force-element method and a vorticity production analysis to develop an enhanced understanding of the influence of each parameter. We observe a direct connection between the amplitude of the lift fluctuation and the vorticity production from the leading edge, due to the surface pressure gradients along the airfoil surface. Notably, the curvature of the airfoil at the leading edge plays a fundamental role in attenuating the extreme aerodynamic loads during the encounter, as it suppresses or enhances the vorticity production levels. In particular, we report a reduction in the magnitude of the lift fluctuations up to 25% for thick airfoil profiles.

BLD and KT acknowledge the support of the Vannevar Bush Faculty Fellowship (N00014-22-1-2798).