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A tale of two airfoils: resolvent-based modelling of an oscillator versus an amplifier from an experimental mean

Symon, Sean and Sipp, Denis and McKeon, Beverley J. (2019) A tale of two airfoils: resolvent-based modelling of an oscillator versus an amplifier from an experimental mean. Journal of Fluid Mechanics, 881 . pp. 81-83. ISSN 0022-1120. https://resolver.caltech.edu/CaltechAUTHORS:20200124-083217262

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Abstract

The flows around a NACA 0018 airfoil at a chord-based Reynolds number of R_e = 10250 and angles of attack of α=0° and α=10° are modelled using resolvent analysis and limited experimental measurements obtained from particle image velocimetry. The experimental mean velocity fields are data assimilated so that they are solutions of the incompressible Reynolds-averaged Navier–Stokes equations forced by Reynolds stress terms which are derived from experimental data. Resolvent analysis of the data-assimilated mean velocity fields reveals low-rank behaviour only in the vicinity of the shedding frequency for α=0° and none of its harmonics. The resolvent operator for the α=10° case, on the other hand, identifies two linear mechanisms whose frequencies are a close match with those identified by spectral proper orthogonal decomposition. It is also shown that the second linear mechanism, corresponding to the Kelvin–Helmholtz instability in the shear layer, cannot be identified just by considering the time-averaged experimental measurements as an input for resolvent analysis due to missing data near the leading edge. For both cases, resolvent modes resemble those from spectral proper orthogonal decomposition when the resolvent operator is low rank. The α=0° case is classified as an oscillator and its harmonics, where the resolvent operator is not low rank, are modelled using parasitic modes as opposed to classical resolvent modes which are the most amplified. The α=10° case behaves more like an amplifier and its nonlinear forcing is far less structured. The two cases suggest that resolvent-based modelling can be achieved for more complex flows with limited experimental measurements.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1017/jfm.2019.747DOIArticle
https://arxiv.org/abs/1904.10131arXivDiscussion Paper
ORCID:
AuthorORCID
Symon, Sean0000-0001-9085-0778
Sipp, Denis0000-0002-2808-3886
McKeon, Beverley J.0000-0003-4220-1583
Alternate Title:A tale of two airfoils: resolvent-based modelling of an oscillator vs. an amplifier from an experimental mean
Additional Information:© 2019 Cambridge University Press. Received 22 April 2019; revised 15 July 2019; accepted 6 September 2019; first published online 24 October 2019. The support of the Army Research Office (ARO) through grant no. W911NF-17-1-0306 and the Office of Naval Research (ONR) through grant no. N00014-17-1-3022 are gratefully acknowledged.
Group:GALCIT
Funders:
Funding AgencyGrant Number
Army Research Office (ARO)W911NF-17-1-0306
Office of Naval Research (ONR)N00014-17-1-3022
Subject Keywords:separated flows, vortex streets, wakes
Record Number:CaltechAUTHORS:20200124-083217262
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200124-083217262
Official Citation:Symon, S., Sipp, D., & McKeon, B. (2019). A tale of two airfoils: Resolvent-based modelling of an oscillator versus an amplifier from an experimental mean. Journal of Fluid Mechanics, 881, 51-83. doi:10.1017/jfm.2019.747
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:100885
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:25 Jan 2020 03:22
Last Modified:25 Jan 2020 03:22

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