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Görtler vortices in low-Reynolds-number flow over multi-element airfoil

Published online by Cambridge University Press:  28 November 2017

Jiang-Sheng Wang ,
Li-Hao Feng Open the ORCID record for Li-Hao Feng [Opens in a new window] ,
Jin-jun Wang Open the ORCID record for Jin-jun Wang [Opens in a new window]  and
Tian Li
Jiang-Sheng Wang
Affiliation:
Key Laboratory of Fluid Mechanics (Beijing University of Aeronautics and Astronautics), Ministry of Education, Beijing 100191, China
Li-Hao Feng
Affiliation:
Key Laboratory of Fluid Mechanics (Beijing University of Aeronautics and Astronautics), Ministry of Education, Beijing 100191, China
Jin-jun Wang*
Affiliation:
Key Laboratory of Fluid Mechanics (Beijing University of Aeronautics and Astronautics), Ministry of Education, Beijing 100191, China
Tian Li
Affiliation:
Key Laboratory of Fluid Mechanics (Beijing University of Aeronautics and Astronautics), Ministry of Education, Beijing 100191, China Shenyang Aircraft Design and Research Institute, Shenyang 110035, China
*
†Email address for correspondence: jjwang@buaa.edu.cn
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Abstract

The low-Reynolds-number flow over a multi-element airfoil (30P30N) is investigated with time-resolved particle image velocimetry (TR-PIV) and flow visualization (FV). Dominant flow structures over the main element of the multi-element airfoil are explored with the variation of angle of attack ( $\unicode[STIX]{x1D6FC}$ ). It is of great importance that Görtler vortices are first observed with this configuration at $\unicode[STIX]{x1D6FC}=2^{\circ }{-}12^{\circ }$ , which is quite different from the high-Reynolds-number cases. The characteristics of the Görtler vortices are explored to determine the origin of these unexpected flow structures. It is found that these Görtler vortices travel in the spanwise direction. Secondary counter-rotating vortices are induced beneath the main Görtler vortices. The travelling property of the Görtler vortices is utilized to determine the positions of the main Görtler vortices and the secondary counter-rotating vortices. It is observed that Görtler vortices reside above the separated shear layer originating from the leading-edge separation of the main element. The secondary counter-rotating vortices are located within the separated shear layer, as a result of the interaction between the Görtler vortices and the separated shear layer. The relative positions of the Görtler vortices, the secondary counter-rotating vortices and the separated shear layer result in a special transition scenario within the separated shear layer. The position of Görtler vortices combined with the Rayleigh discriminant indicates the mechanism that the Görtler vortices are generated by a virtual curved boundary. The travelling property of the Görtler vortices, which is different from the classical stationary Görtler vortices, can also be interpreted by this mechanism. Ultimately, modified criteria for generating Görtler vortices with a virtual curved boundary are proposed to provide references for the follow-up works.

JFM classification

Aerodynamics: Aerodynamics Instability: Instability Vortex Flows: Vortex interactions

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JFM Papers
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Journal of Fluid Mechanics , Volume 835 , 25 January 2018 , pp. 898 - 935
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© 2017 Cambridge University Press 

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