GALCIT Colloquium

Highly unsteady flows over lifting surfaces are common in a wide variety of applications including large- and small-scale aircraft, underwater vehicles, wind and tidal turbines, and bio-inspired flying and swimming. Large changes in flow magnitude or direction, however, are difficult to model because they often result in flow separation and the formation of strong vortices and complex wakes. The current work applies tools from fundamental aerodynamics to a series of canonical problems in order to quantify the relative importance of coherent structures in the flow field and identify the flow physics responsible for unsteady loading. These results are summarized in a physics-based reduced order model of the forcing transients. This improved understanding of the physical mechanisms by which unsteady loading is generated provides insight into the potential for implementing control to attenuate forcing transients. Specifically, we will look closely at dynamic stall in the reverse flow region of a high advance ratio rotor and make comparisons to two more canonical problems: a surging wing and a transverse gust encounter. In each of these cases, flow separation and the generation of vorticity at the leading edge of the wing results in a strong leading-edge vortex that is largely responsible for the transients observed in aerodynamic loading. Based on our understanding of the underlying physics of this force generation, we outline a plan to develop nonlinear control laws to regularize loading transients. The aim of this work is to expand the flight envelope of air and water vehicles operating in unsteady aerodynamic environments, thereby enabling safer and more robust flight in complex terrain, extreme weather, and wakes.