Physics and Computational Modeling of Nonlinear Transverse Gust Encounters

Abstract

The next generation of unmanned aerial vehicles (UAV) will have missions 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 success of future UAV development. This paper explores the numerical simulation of transverse gusts using a modified boundary condition in a state-of-the art computational fluid dynamics (CFD) solver. The modified boundary condition generates a transverse top-hat jet with velocity (W) through which a flat plate wing is ``towed'' through the jet at velocity (U), mimicking a transverse gust. Mesh independence and sensitivities are examined, as well as several angles of attack . Results from numerical simulations are compared and validated against towed wing-gust encounter experiments at the University of Cambridge. The new approach is shown to be valid and accurate. The maximum lift is shown to correlate linearly with gust ratio. Distributed vorticity analyses confirm that non-circulatory terms over the gust remain constant for all gust scenarios and with the inclusion of viscous effects, supporting the original assumption from Kussner theory.