Experiments in vortex formation of plunging & flapping flat plates

Date of Award

2008

Degree Name

M.S. in Aerospace Engineering

Department

Department of Mechanical and Aerospace Engineering

Advisor/Chair

Advisor: Aaron Altman

Abstract

Reynolds number, Strouhal number, and formation number are insufficient to quantify the flow properties of a flapping wing system. These parameters do not take enough information from the input variables into account. As part of the current study, the velocity profile and angle of attack were varied during a single pure plunge flapping stroke using an infinite aspect ratio flat plate. Although the velocity profile was either a constant velocity or quarter-sine velocity, the average Reynolds number was held constant at 3000. Strong differences in the flow structure, both qualitatively and quantitatively, were obtained. A new metric is proposed that is able to take these differences in the input variables into account. This metric utilizes the theory of maximum work potential and statistical regressions of the experimental data in order to obtain a model of the experimental parameter space. With this model, estimates of the desired outputs can be made given values for the inputs. The main portion of this study focuses on the differences in flow structure, using qualitative and quantitative techniques, due to finite aspect ratio and flapping about a hinge point. Data at various spanwise and chordwise locations were taken in order to analyze the leading edge, trailing edge, and tip vortices. A small study was also conducted on the effects of changing Reynolds number. It was found that for the infinite aspect ratio plate, using a quarter-sine velocity profile, instead of a constant velocity profile, enhances the production of circulation. Operating at a slight angle of attack (85⁰ instead of 90⁰) also enhances circulation production; however, operating at a large angle of attack (60⁰ instead of 90⁰) has the opposite effect due to pinch-off of both the leading and trailing edge vortices. Hinging the wing at the root and using a finite aspect ratio causes the constant velocity profile to produce higher values of circulation than the quarter-sine velocity profile. This trend is the opposite of that seen for the infinite aspect ratio cases. It was also found that flapping in this highly three-dimensional manner greatly hinders the production of circulation as compared to the infinite aspect ratio, pure plunge experiments.

Keywords

Vortex-motion, Reynolds number, Angle of attack (Aerodynamics)

Rights Statement

Copyright © 2008, author

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