Dynamics of laminar separation bubble over NACA-0012 airfoil near stall conditions

High-fidelity large eddy simulation is carried out for the flow field around a NACA-0012 aerofoil at Reynolds number of [Formula: see text], Mach number of 0.4, and various angles of attack around the onset of stall. The laminar separation bubble is formed on the suction surface of the aerofoil and is constituted by the reattached shear layer. At these conditions, the laminar separation bubble is unstable and switches between a short bubble and an open bubble. The instability of the laminar separation bubble triggers a low-frequency flow oscillation. The aerodynamic coefficients oscillate accordingly at a low frequency. The lift and the drag coefficients compare very well to recent high-accuracy experimental data, and the lift leads the drag by a phase shift of [Formula: see text]. The mean lift coefficient peaks at the angle of attack of [Formula: see text], in total agreement with the experimental data. The spectra of the lift coefficient does not show a significant low-frequency peak at angles of attack lower than or equal the stall angle of attack ([Formula: see text]). At higher angles of attack, the spectra show two low-frequency peaks and the low-frequency flow oscillation is fully developed at the angle of attack of [Formula: see text]. The behaviour of the flow-field and changes in the turbulent kinetic energy over one low-frequency flow oscillation cycle are described qualitatively.

Download Full-text

Simulation and characterization of the laminar separation bubble over a NACA-0012 airfoil as a function of angle of attack

Physical Review Fluids ◽

10.1103/physrevfluids.6.034701 ◽

2021 ◽

Vol 6 (3) ◽

Author(s):

Eltayeb Eljack ◽

Julio Soria ◽

Yasir Elawad ◽

Tomohisa Ohtake

Keyword(s):

Separation Bubble ◽

Angle Of Attack ◽

Laminar Separation Bubble ◽

Laminar Separation ◽

Naca 0012

Download Full-text

Oscillating behaviour of laminar separation bubble formed on an aerofoil near stall

The Aeronautical Journal ◽

10.1017/s0001924000151607 ◽

2004 ◽

Vol 108 (1081) ◽

pp. 153-163 ◽

Cited By ~ 30

Author(s):

K. Rinoie ◽

N. Takemura

Keyword(s):

Separation Bubble ◽

Angle Of Attack ◽

Leading Edge ◽

Chord Length ◽

Flow Visualisation ◽

Laminar Separation Bubble ◽

Mean Velocity ◽

Laminar Separation ◽

Naca 0012 ◽

Small Separation

Abstract Laminar separation bubbles formed on NACA 0012 aerofoil near the onset of a stall were investigated to clarify the behaviour of the laminar separation bubble. Measurements were done at a chord Reynolds number of 1·3 × 105. Mean velocity measurements indicate that the long bubble of about 35% chord length is formed at α = 11·5° after the short bubble burst occurred. However, the instantaneous flow visualisation picture indicates that the flow is strongly oscillating at this angle of attack. The phase averaging technique has been applied to analyse this oscillating behaviour. The results indicate that the flow is oscillating between a small separation-reattachment bubble formed near the leading-edge at about a 10% chord length and a large separated region extending over the aerofoil surface. It is suggested that this small separation-reattachment bubble has a similar flow structure to that of the short bubble formed at a lower angle of attack.

Download Full-text

Oscillating behaviour of laminar separation bubble formed on an aerofoil near stall

The Aeronautical Journal ◽

10.1017/s0001924000000063 ◽

2004 ◽

Vol 108 (1081) ◽

pp. 153-163 ◽

Cited By ~ 29

Author(s):

K. Rinoie ◽

N. Takemura

Keyword(s):

Separation Bubble ◽

Angle Of Attack ◽

Leading Edge ◽

Chord Length ◽

Flow Visualisation ◽

Laminar Separation Bubble ◽

Mean Velocity ◽

Laminar Separation ◽

Naca 0012 ◽

Small Separation

AbstractLaminar separation bubbles formed on NACA 0012 aerofoil near the onset of a stall were investigated to clarify the behaviour of the laminar separation bubble. Measurements were done at a chord Reynolds number of 1·3 × 105. Mean velocity measurements indicate that the long bubble of about 35% chord length is formed at α = 11·5° after the short bubble burst occurred. However, the instantaneous flow visualisation picture indicates that the flow is strongly oscillating at this angle of attack. The phase averaging technique has been applied to analyse this oscillating behaviour. The results indicate that the flow is oscillating between a small separation-reattachment bubble formed near the leading-edge at about a 10% chord length and a large separated region extending over the aerofoil surface. It is suggested that this small separation-reattachment bubble has a similar flow structure to that of the short bubble formed at a lower angle of attack.

Download Full-text