Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session F25: Instability: Boundary Layers
8:00 AM–10:10 AM,
Monday, November 19, 2018
Georgia World Congress Center
Room: B313
Chair: Jovan Nedic, McGill University
Abstract ID: BAPS.2018.DFD.F25.2
Abstract: F25.00002 : Non-modal stability analysis of low-Re separated flow around a NACA 4415 airfoil in ground effect*
8:13 AM–8:26 AM
Presenter:
Wei He
(Hong Kong University of Science and Technology)
Authors:
Wei He
(Hong Kong University of Science and Technology)
Jóse Miguel Pérez
(Technical University of Madrid)
Peng Yu
(Southern University of Science and Technology)
Larry K.B. Li
(Hong Kong University of Science and Technology)
In this numerical-theoretical study, we perform a linear non-modal stability analysis of the separated flow around a NACA 4415 airfoil over a no-slip ground at low Reynolds numbers (300≤Re≤500) and high angles of attack (15° ≤α≤20°). We find that: (i) the strength of the recirculation zone behind the airfoil is a key parameter controlling the absolute/convective nature of the instability in the boundary layer downstream; (ii) when Re, α or the ground clearance increases, the energy gain also increases, with the optimal perturbations switching from being three dimensional to two dimensional; and (iii) classical hairpin vortices, or Klebanoff modes, can be produced by three-dimensional optimal perturbations on a two-dimensional steady base flow containing a laminar separation bubble. Knowledge of the spatiotemporal properties of the optimal mode could aid the design of advanced strategies for flow control. This study offers new insight into the transient growth behavior of airfoil-ground flow systems at low Re and high α, contributing to a better understanding of the ground-effect aerodynamics of small insects and micro aerial vehicles.
*We would like to thank the Research Grants Council of Hong Kong (Project Numbers 16235716 and 26202815) for their financial support.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2018.DFD.F25.2
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