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The unsteady lift of an oscillating airfoil encountering a sinusoidal streamwise gust

Published online by Cambridge University Press:  08 December 2020

Ruwei Ma Open the ORCID record for Ruwei Ma [Opens in a new window] ,
Yang Yang Open the ORCID record for Yang Yang [Opens in a new window] ,
Mingshui Li Open the ORCID record for Mingshui Li [Opens in a new window]  and
Qiusheng Li Open the ORCID record for Qiusheng Li [Opens in a new window]
Ruwei Ma
Affiliation:
Research Centre for Wind Engineering, Southwest Jiaotong University, Chengdu610031, PR China
Yang Yang
Affiliation:
Research Centre for Wind Engineering, Southwest Jiaotong University, Chengdu610031, PR China Key Laboratory for Wind Engineering of Sichuan Province, Chengdu610031, PR China
Mingshui Li*
Affiliation:
Research Centre for Wind Engineering, Southwest Jiaotong University, Chengdu610031, PR China Key Laboratory for Wind Engineering of Sichuan Province, Chengdu610031, PR China
Qiusheng Li*
Affiliation:
Department of Architecture and Civil Engineering, City University of Hong Kong, Kowloon, Hong Kong
*
†Email addresses for correspondence: [email protected], [email protected]
†Email addresses for correspondence: [email protected], [email protected]
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Abstract

The unsteady lift of an oscillating airfoil encountering a sinusoidal streamwise gust is experimentally investigated. The sinusoidal streamwise gust is generated by a multiple-fan actively controlled wind tunnel. A two-dimensional airfoil with a NACA0015 profile oscillates in the wind tunnel with a pitch motion frequency of $f_v=1\ \textrm {Hz}$ while the sinusoidal streamwise gust has a different oscillating frequency of $f_{\beta }=1.7\ \textrm {Hz}$. The non-dimensional unsteady lift coefficients determined from surface pressure show the same trends as Greenberg's prediction. Through spectral analysis, the sum frequency $f_{sum}=f_{\beta }+f_v$ and the difference frequency $f_{diff}=|f_{\beta }-f_v|$, proposed by Greenberg, are firstly observed in the experiment. The experimental results are compared with Greenberg's theory in the case of a small amplitude of gust velocity variation $\sigma =0.2$. The results of all cases indicate that the experimental results agree generally well with Greenberg's prediction, while there is a small deviation.

Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 908 , 10 February 2021 , A22
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Copyright
© The Author(s), 2020. Published by Cambridge University Press

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