Computational Validation and Assessment of Large Amplitude Transverse Gust Physics

Abstract

Rotary-wing vehicles, in particular smaller, lighter unmanned and urban air vehicles in urban and shipboard settings, will operate in low-speed flight conditions that are dominated by strong transient aerodynamics. Understanding the physics of these transient aerodynamics, specifically large amplitude transverse gusts and the resulting vehicle response, is crucial to the successful development and certification of safe air vehicles that operate in these environments. A high-fidelity computational study, including validation with experiments, explores sharp-edged or step transverse gusts where the gust velocity induces nonlinear behavior caused by flow separation. The behavior of the maximum lift and leading edge vortex behavior with the gust ratio is presented. Gust responses are observed to depart from Küssner's theory when the leading edge vortex first forms as a distinct feature and breaks away from the wing, resulting in flow nonlinearities. Traditional linear indicial admittance techniques are shown to no longer be valid to predict gust responses when the gust velocity approaches the vehicle flight speed.