DOI

10.17077/etd.xhdj-14k7

Document Type

Thesis

Date of Degree

Spring 2019

Degree Name

MS (Master of Science)

Degree In

Mechanical Engineering

First Advisor

Buchholz, James H.

First Committee Member

Lamuta, Caterina

Second Committee Member

Udaykumar, H.S.

Abstract

The leading-edge vortex (LEV) is a structure found in unsteady aerodynamics that can alter the forces induced on wings and other rotating structures. This thesis presents an experimental study on LEV development on low aspect-ratio wing rolling in a uniform flow at high angles of attack. The flow structure dynamics of rotating wings in the presence of a free stream are not well understood due to the limited studies under these conditions. In this study, a broad parameter space with varying advance ratio and wing radius of gyration are analyzed using dye-visualizations. In most cases, either a conical LEV structure developed on the inboard part of the wing and persisted to a significant roll angle, as well as the arch structure. Plenoptic PIV was used to validate observations in flow visualizations as well as identify finer structures. A binary classification criterion was defined based on the formation and persistence of the inboard conical LEV structure. This criterion identified the LEV as either conical ,non-conical or transitional. Previous studies inspired the proposal of a ”rotation parameter” ,ΠRot, that was a based on a non-dimensional velocity gradient. A value of ΠRot = 0.17 was found to separate conical and non-conical LEV parameter, suggesting the fundamental importance of this parameter to LEV dynamics. Furthermore, the forces were analyzed to understand the impact of the flow structure on the forces. The conical LEVs had a transient peak followed by irregular udulations while the non-conical LEVs produced high frequency oscillations. In both cases, the force could be understood based on the time-evolution of the LEVs.

Passive bleeding was considered within this study to perturb the flow. Four passive bleed configurations were experimented with at different hole locations and sizes. It was found that a hole applied near the wing root with a large diameter perturbed the flow and transformed the structure from conical to non-conical classifications. This provides a platform to further understand the flow mechanisms that govern LEV formation and evolution by drastically changing flow structures and maintaining the same geometric and kinematic parameters. Additional studies were done analyzing the changes on the forces on the wing. The lift on the passive bleeding did not seem to be affected however, the thrust was decreased to nearly 0.

Keywords

Aerodynamic, Free Stream, Leading-Edge, Parameter, Rolling, Vortex

Pages

ix, 45 pages

Bibliography

Includes bibliographical references (pages 44-45).

Comments

This thesis has been optimized for improved web viewing. If you require the original version, contact the University Archives at the University of Iowa: https://www.lib.uiowa.edu/sc/contact/.

Copyright

Copyright © 2019 Randall Berdon

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