Gust encounter flow physics with applications to flow sensing and control

Abstract

Systems such as aircraft and wind turbines frequently operate in highly unsteady flow environments and are subject to large flow disturbances, such as gusts. Gust encounters can lead to severe performance degradation and, in extreme cases, catastrophic failure. This dissertation investigates the fundamental flow physics underlying wing-gust encounter aerodynamics and explores strategies for effective flow sensing and gust mitigation. Emphasis is placed on the development and use of inviscid methods to facilitate the detection, prediction, and alleviation of incident gusts. The first part of the dissertation experimentally investigates the unsteady loads and flowfields produced during transverse gust encounters and evaluates the effectiveness of inviscid aerodynamics theory. In particular, experimental lift transients and shed vorticity distributions are compared with those predicted by Kussner's transverse gust model. The results show that in the early stages of the gust encounter Kussner's inviscid model captures the circulation production of the separated, viscous flow which produces favorable agreement between experimental and theoretical lift transients. The performance of Kussner's model deteriorates during the wing's exit from the gust due to contrasting shed vorticity distributions between the model and the experiments, resulting in fundamentally different lift reduction mechanisms. Building on these findings, the dissertation investigates how vorticity in the flow affects the wing's surface pressure distribution during a gust encounter. Simultaneous surface pressure, load, and flow measurements are presented, and their concurrent analysis details the events leading to flow separation and leading-edge vortex (LEV) formation. In particular, surface pressure-derived quantities—such as leading-edge suction and the leading-edge pressure gradient—are examined in their ability to sense key flow structures and detect gusts. The final part of the dissertation centers on the development and application of inviscid modeling methods to explore the physics of flow separation and to design effective strategies for flow sensing and control. Three key applications are addressed: (1) A numerical inviscid method incorporating the effects of leading-edge separation is developed to compute unsteady surface pressure distributions during gust encounters; (2) an analytical vortex sheet model is introduced, relating the growth of the leading-edge vortex sheet to the pressure coefficient at the leading edge, enabling LEV detection and strength estimation, and (3) Theodorsen's inviscid model is combined with an iterative optimization method developed by collaborators, to experimentally identify optimal gust-mitigating pitch and plunge maneuvers.