Effect of trailing edge shape on the separated flow characteristics around an airfoil at low Reynolds number: A numerical study

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Title: Effect of trailing edge shape on the separated flow characteristics around an airfoil at low Reynolds number: A numerical study
Authors: Thomareis, N
Papadakis, G
Item Type: Journal Article
Abstract: Direct numerical simulations of the flow field around a NACA 0012 airfoil at Reynolds number 50 000 and angle of attack 5° with 3 different trailing edge shapes (straight, blunt, and serrated) have been performed. Both time-averaged flow characteristics and the most dominant flow structures and their frequencies are investigated using the dynamic mode decomposition method. It is shown that for the straight trailing edge airfoil, this method can capture the fundamental as well as the subharmonic of the Kelvin-Helmholtz instability that develops naturally in the separating shear layer. The fundamental frequency matches well with relevant data in the literature. The blunt trailing edge results in periodic vortex shedding, with frequency close to the subharmonic of the natural shear layer frequency. The shedding, resulting from a global instability, has an upstream effect and forces the separating shear layer. Due to forcing, the shear layer frequency locks onto the shedding frequency while the natural frequency (and its subharmonic) is suppressed. The presence of serrations in the trailing edge creates a spanwise pressure gradient, which is responsible for the development of a secondary flow pattern in the spanwise direction. This pattern affects the mean flow in the near wake. It can explain an unexpected observation, namely, that the velocity deficit downstream of a trough is smaller than the deficit after a protrusion. Furthermore, the insertion of serrations attenuates the energy of vortex shedding by de-correlating the spanwise coherence of the vortices. This results in weaker forcing of the separating shear layer, and both the subharmonics of the natural frequency and the shedding frequency appear in the spectra.
Issue Date: 17-Jan-2017
Date of Acceptance: 26-Dec-2016
URI: http://hdl.handle.net/10044/1/43747
DOI: https://dx.doi.org/10.1063/1.4973811
ISSN: 1089-7666
Publisher: AIP Publishing
Journal / Book Title: Physics of Fluids
Volume: 29
Issue: 1
Copyright Statement: © 20167 The Author(s). Published by AIP Publishing.
Sponsor/Funder: Commission of the European Communities
Funder's Grant Number: FP7 - 317269
Keywords: Fluids & Plasmas
01 Mathematical Sciences
02 Physical Sciences
09 Engineering
Publication Status: Published
Article Number: 014101
Appears in Collections:Faculty of Engineering
Aeronautics



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