Unsteady Physics and Aeroelastic Response of Streamwise Vortex-Surface Interactions

by Caleb J. Barnes

Institution: Wright State University
Department: Engineering PhD
Degree: PhD
Year: 2015
Keywords: Mechanical Engineering; Fluid Dynamics; Aerospace Engineering; formation flight; streamwise vortex interaction; fluid structure interaction; aeroelasticity; unsteady fluid dynamics; vortex dynamics; vortex surface interaction
Record ID: 2058648
Full text PDF: http://rave.ohiolink.edu/etdc/view?acc_num=wright1431937866


Streamwise vortex-surface interactions can occur in aviation intentionally in the context of formation flight as an energy saving mechanism, unintentionally in wake crossings when aircraft fly in close proximity, and as a consequence of aircraft design through the interaction of fluid dynamics between different aerodynamic surfaces. The bulk of past work on streamwise vortex-surface interactions has focused on steady inviscid analysis for optimizing aerodynamic loads in the context of formation flight or experimental analysis on fin buffeting problems. A fundamental understanding of the viscous and unsteady effects that may occur is both important and currently lacking in the literature. This dissertation seeks to fill this need by using a high-fidelity implicit large-eddy simulation approach coupled with geometrically non-linear finite elements to identify and analyze important physics that may occur. Simple, canonical configurations are employed in order help disentangle the many interrelated factors of a very complex problem. Analysis of a tandem wing configuration elucidated mutual induction between the incident vortex from the leader wing and tip vortex of the follower wing that resulted in a broad taxonomy of flow structure, wake evolution, and unsteady behaviors for several lateral impingement locations. Interaction of an isolated streamwise vortex with a wing revealed a robust helical instability develops when a strong vortex impinges directly with the leading-edge. This spiraling behavior was found to occur as a result of the upstream influence of adverse pressure gradients provided by the wing that drive the vortex into its linearly unstable regime allowing for the growth of shortwave perturbations. Stability can be augmented through vertical positioning of the vortex. A negative offset can enhance stability by providing a stronger adverse pressure gradient while a positive offset exploits a favorable gradient and removes the upstream instability altogether. The effects of wing compliance were revealed through full aeroleastic simulations. Essentially static, vortex-induced bending deformations reposition the vortex and drive it further into its unstable regime. Static and dynamic components of the aeroelastic response were systematically isolated where the static deformations were shown to provide the greatest influence. Dynamic effects provide some influence to the incident vortex behavior but these are secondary to the static behavior.