High fidelity optimization of flapping airfoils and wings
Abstract/Contents
- Abstract
- Flapping wings are interesting in many ways from both a scientific and an engineering perspective. They are also challenging to design and analyze due to the inherent complexity of both the kinematic motion of the wing and the resulting vortex-dominated fluid dynamics. One way to study flapping wings is to use an optimization approach to find kinematic motions that lead to efficient flight under various conditions. We use this approach, coupling high-fidelity 2D and 3D Navier-Stokes solvers with a gradient-based optimization algorithm. Results are presented for several optimizations of 2D airfoils and 3D wings undergoing periodic, flapping-type motions. In 2D the pitching and plunging NACA0012 airfoil case is considered, with optimizations being carried out to maximize propulsive efficiency and also to minimize input power given a target thrust constraint. In 3D rectangular and semi-elliptic wings of varying thickness that are hinged at the root are considered. The motion of the 3D wing is parameterized by spline control points that allow span-wise variation of twist, dihedral and sweep, allowing complex wing motions and deformations with relatively few parameters. Propulsive efficiency is maximized for the 3D wing in a non-twisting case as well as using one, two and four of these span-wise twist control points, and a case with one each of twist, dihedral and sweep control points. Wing thickness and planform effects are also considered, with optimizations being carried out for both $12\%$ thick and $2\%$ thick airfoil sections and using rectangular and semi-elliptic planform wings. The results of the optimizations lead to several conclusions, including that pitching and twisting can significantly improve the attainable propulsive efficiency, that twisting motions beyond a certain level of complexity offer no additional improvement in attainable propulsive efficiency, and that sweeping motions also do not increase attainable propulsive efficiency. Analysis of the flow physics of the optimal cases show that the high-performing cases operate in the absence of a persistent leading-edge vortex, but do display a stable, thin boundary region of recirculation during the middle portion of the stroke that destabilizes into shed vortices at the top and bottom of the stroke. The destabilization of this region is shown to be highly sensitive to variations in wing motion and geometry.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2013 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Culbreth, Matthew |
|---|---|
| Associated with | Stanford University, Department of Aeronautics and Astronautics. |
| Primary advisor | Jameson, Antony, 1934- |
| Thesis advisor | Jameson, Antony, 1934- |
| Thesis advisor | Alonso, Juan José, 1968- |
| Thesis advisor | Pulliam, T. H. (Thomas H.), 1951- |
| Advisor | Alonso, Juan José, 1968- |
| Advisor | Pulliam, T. H. (Thomas H.), 1951- |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Matthew Culbreth. |
|---|---|
| Note | Submitted to the Department of Aeronautics and Astronautics. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2013. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2013 by Matthew Kohler Culbreth
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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