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Experimental Generation and Modeling of Vortical Gusts and Their Interactions with an Airfoil

Citation

Hufstedler, Esteban Antonio Lemus (2017) Experimental Generation and Modeling of Vortical Gusts and Their Interactions with an Airfoil. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9Q52MN5. http://resolver.caltech.edu/CaltechTHESIS:05232017-111820349

Abstract

This thesis examines two methods of vortical gust generation and the interaction between these gusts and an airfoil. These flows were studied with both experiments at a Reynolds number of 20,000 and with potential-flow based simulations.

The standard method of generating a vortical gust has been to rapidly pitch an airfoil. A novel approach is presented: heaving a plate across the tunnel, and changing direction rapidly to release a vortex. This method is motivated by the desire to limit a test article's exposure to the wake of the gust generator by moving it to the side of the tunnel.

A series of potential flow models were used to examine these flows: steady and unsteady thin airfoil theory, an extension of Tchieu and Leonard's unsteady airfoil model, and an unsteady vortex panel method.

Experiments characterized the generated gusts and verified that the strength of the shed vortices approximately matched the theoretical predictions. The inviscid simulations were unable to predict viscous effects like the wakes of the generators. The pitching airfoil resulted in a persistent wake in the test section, whereas the wake of the heaving plate only temporarily disturbed the flow.

The vortex-wing interaction was examined using both mechanisms. When the wake of the generator was far from the wing, the unsteady simulations provided reasonable estimates for the early variation in lift. This demonstrated that the initial lift peak is due to inviscid effects. Each of the potential flow methods with wake models provided reasonable estimates of this lift. The simplicity of the unsteady thin airfoil theory model recommends its use for examining early vortex-wing interactions.

With the test article mounted at the midline of the tunnel, the wakes had substantial effects when the pitching generator was near the midline of the tunnel, or when the heaving plate passed the midline. The simulations were not able to capture the effects of the wakes or predict the effects of the airfoil's angle of attack. This had the largest effect on the timescale of the post-gust approach to the final forces. With the airfoil at α=0°, this was 5-10 convective time units, which is characteristic of attached flows. The airfoil at α=10° needed double the time to approach its final state after perturbations due to its separated flow. The heaving plate's withdrawal allowed for measurement of the resumption of vortex shedding, which was impossible with the pitching airfoil's persistent wake.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:unsteady aerodynamics; vortex; gust
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Aeronautics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • McKeon, Beverley J.
Group:Graduate Aerospace Laboratories
Thesis Committee:
  • Gharib, Morteza (chair)
  • Colonius, Timothy E.
  • Leonard, Anthony
  • McKeon, Beverley J.
Defense Date:2 May 2017
Funders:
Funding AgencyGrant Number
Gordon and Betty Moore Foundation2645
Record Number:CaltechTHESIS:05232017-111820349
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:05232017-111820349
DOI:10.7907/Z9Q52MN5
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.2514/6.2016-4257DOIThis article covers a portion of the research described in the thesis. Figure 4.13 in the thesis is reproduced from this article.
ORCID:
AuthorORCID
Hufstedler, Esteban Antonio Lemus0000-0001-7162-920X
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10194
Collection:CaltechTHESIS
Deposited By: Esteban Hufstedler
Deposited On:05 Jun 2017 21:34
Last Modified:12 Jun 2017 20:54

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