Analysis of flow timescales on a periodically pitching/surging airfoil

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Title: Analysis of flow timescales on a periodically pitching/surging airfoil
Author(s): Dunne, R
Schmid, PJ
McKeon, BJ
Item Type: Journal Article
Abstract: Time-resolved velocity fields around a pitching and surging NACA 0018 airfoil were analyzed to investigate the influence of three independent timescales associated with the unsteady flowfield. The first of these timescales, the period of the pitch/surge motion, is directly linked to the development of dynamic stall. A simplified model of the flow using only a time constant mode and the first two harmonics of the pitch surge frequency has been shown to accurately model the flow. Full stall and leading-edge flow separation, however, were found to take place before the maximum angle of attack, indicating that a different timescale was associated with leading-edge vortex formation. This second, leading-edge vortex, timescale was found to depend on the airfoil convection time and compare well with the universal vortex formation time. Finally, instantaneous non-phase-averaged measurements were investigated to identify behavior not directly coupled to the airfoil motion. From this analysis, a third timescale associated with quasi-periodic Strouhal vortex shedding was found before flow separation. The interplay between these three timescales is discussed in detail, particularly as they relate to the periodic velocity and angle-of-attack change apparent to the blades of a vertical axis wind turbine.
Publication Date: 18-Jul-2016
Date of Acceptance: 29-Apr-2016
URI: http://hdl.handle.net/10044/1/39113
DOI: https://dx.doi.org/10.2514/1.J054784
ISSN: 0001-1452
Start Page: 3421
End Page: 3433
Journal / Book Title: AIAA Journal
Volume: 54
Issue: 11
Copyright Statement: © 2016 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Copies of this paper may be made for personal and internal use, on condition that the copier pay the per-copy fee to the Copyright Clearance Center (CCC). All requests for copying and permission to reprint should be submitted to CCC at www.copyright.com; employ the ISSN 0001-1452 (print) or 1533-385X (online) to initiate your request.
Keywords: Science & Technology
Technology
Engineering, Aerospace
Engineering
LOW-REYNOLDS-NUMBER
AXIS WIND TURBINE
OSCILLATING AIRFOIL
DYNAMIC STALL
VORTEX
WAKE
PIV
Aerospace & Aeronautics
0901 Aerospace Engineering
0913 Mechanical Engineering
Publication Status: Published
Appears in Collections:Mathematics
Applied Mathematics and Mathematical Physics
Faculty of Natural Sciences



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