Dynamic Response of a Free-flying Airfoil to Prescribed Vortex Gusts*

The unfavorable interaction of modern aircraft with vortex gusts is an increasingly important issue as aircraft become smaller, more lightweight, flexible, and agile. In this work, an airfoil's dynamic response to a disturbance is studied experimentally in a water flume using a two-foil system, and results are compared with numerical simulations. The upstream foil acts as a disturbance generator that produces a vortex gust of desired strength, sign, and location by following a prescribed heaving and pitching trajectory. The downstream airfoil is controlled experimentally by a force-feedback cyber-physical system (CPS) that enables it to “freely fly” – to move in response to flow disturbances and realistic flight dynamics. Using Particle Image Velocimetry (PIV) we first validate the vortex generator to ensure a single coherent vortex with desired characteristics is produced. Secondly, we characterize the forces experienced by a constrained airfoil as a vortex impinges on it and we compare this with classic unsteady aerodynamics models. Finally, the dynamic response of a two-degree-of-freedom CPS free-flying airfoil in which the wing can pitch and heave in response to a gust is characterized.