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research-article

Shear Layer Development, Separation, and Stability Over a Low-Reynolds Number Airfoil

[+] Author and Article Information
Paul Ziade

Instructor, Department of Mechanical & Manufacturing Engineering, University of Calgary, Calgary, Alberta, Canada T2N 1N4
paul.ziade@ucalgary.ca

Mark A. Feero

Postdoctoral Research Associate, Department of Mechanical Engineering, Michigan State University, East Lansing, Michigan, USA 48824
m.feero@mail.utoronto.ca

Philippe Lavoie

Associate Professor, Institute for Aerospace Studies, University of Toronto, Toronto, Ontario, Canada M5S 1A4
lavoie@utias.utoronto.ca

Pierre E. Sullivan

Professor, Department of Mechanical & Industrial Engineering, University of Toronto, Toronto, Ontario, Canada M5S 3G8
sullivan@mie.utoronto.ca

1Corresponding author.

ASME doi:10.1115/1.4039233 History: Received August 23, 2017; Revised January 05, 2018

Abstract

The shear layer development for a NACA 0025 airfoil at a low Reynolds number was investigated experimentally and numerically using large-eddy simulation. Two angles-of-attack were considered: 5 and 12 degrees. Experiments and numerics confirm that two flow regimes are present. The first regime, present for an angle-of-attack of 5 degrees, exhibits boundary layer reattachment with formation of a laminar separation bubble. The second regime consists of boundary layer separation without reattachment. Linear stability analysis of mean velocity profiles is shown to provide adequate agreement between measured and computed growth rates. The stability equations exhibit significant sensitivity to variations in the base flow. This highlights that caution must be applied when experimental or computational uncertainties are present, particularly when performing comparisons. Linear stability analysis suggests that the first regime is characterized by high frequency instabilities with low spatial growth, whereas the second regime experiences low frequency instabilities with more rapid growth. Spectral analysis confirms the dominance of a central frequency in the laminar separation region of the shear layer, and the importance of nonlinear interactions with harmonics in the transition process.

Copyright (c) 2018 by ASME
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