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

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

scholarly journals Numerical investigation of the low-frequency flow oscillation over a NACA-0012 aerofoil at the inception of stall

2019 ◽  
Vol 11 ◽  
pp. 175682931983368 ◽  
Author(s):  
Yasir A ElAwad ◽  
Eltayeb M ElJack
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Separation Bubble ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Low Frequency ◽  
Laminar Separation Bubble ◽  
Flow Oscillation ◽  
Laminar Separation ◽  
Naca 0012

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.

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

2004 ◽  
Vol 108 (1081) ◽  
pp. 153-163 ◽  
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.

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

2004 ◽  
Vol 108 (1081) ◽  
pp. 153-163 ◽  
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.

Characterization of Vortex Dynamics in a Laminar Separation Bubble

AIAA Journal ◽  
2017 ◽  
Vol 55 (8) ◽  
pp. 2664-2675 ◽  
Author(s):  
Andrew R. Lambert ◽  
Serhiy Yarusevych
Keyword(s):  
Vortex Dynamics ◽  
Separation Bubble ◽  
Laminar Separation Bubble ◽  
Laminar Separation

scholarly journals Laminar Separation Bubble and Flow Topology of NACA 0015 at Low Reynolds Number

CFD Letters ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 36-51
Author(s):  
Mohamed Ibren ◽  
Amelda Dianne Andan ◽  
Waqar Asrar ◽  
Erwin Sulaeman
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Flow Field ◽  
Separation Bubble ◽  
Low Reynolds Number ◽  
Angle Of Attack ◽  
Laminar Separation Bubble ◽  
Laminar Separation ◽  
Low Reynolds ◽  
Naca 0015

The development of sophisticated unmanned aerial vehicles and wind turbines for daily activities has triggered the interest of researchers. However, understanding the flow phenomena is a strenuous task due to the complexity of the flow field. The engaging topic calls for more research at low Reynolds numbers. The computational investigations on a two-dimensional (2D) airfoil are presented in this paper. Numerical simulation of unsteady, laminar-turbulent flow around NACA 0015 airfoil was performed by using shear-stress transport (SST) model at relatively low Reynolds number (8.4 × 104 to 1.7 × 105) and moderate angles of attack (0 ≤ α ≤ 6). In general, on the suction side, with increasing Reynolds number and angles of attack, separation, and reattachment point shifts upstream and concurrently shrinking the size of the laminar bubble. However, On the pressure side, the laminar bubble is seen to move toward the trailing edge at the relatively same size as the angle of attack increases. Moreover, the variations in the angle of attack have more influence on the laminar separation bubble characteristics as compared to the Reynolds number. The reattachment points were barely observed for the range of the angles of attack studied. At very high angles of attack, it is recommended to simulate the flow field using large eddy simulation or direct numerical simulation since the flow is considered three-dimensional and detached from the surface thus forming a complex phenomenon.

Experimental Investigations of Laminar Separation Bubble for a Flow Past an Airfoil

2010 ◽  
Author(s):  
Deepakkumar M. Sharma ◽  
Kamal Poddar
Keyword(s):  
Boundary Layer ◽  
Flow Separation ◽  
Separation Bubble ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Boundary Layer Separation ◽  
Experimental Investigations ◽  
Stream Velocity ◽  
Laminar Separation Bubble ◽  
Laminar Separation

Wind tunnel experiments were carried out on NACA 0015 airfoil model to investigate the formation of laminar separation bubble on the upper surface of the airfoil by varying angle of attack from −5° to 25° with respect to the free stream velocity at constant Reynolds number varying from 0.2E06 to 0.6E06. Pressure signals were acquired from the pressure ports selected at the mid-span of the airfoil model along the chord. Static stall characteristics were obtained from the surface pressure distribution. The flow separation was found to be a trailing edge turbulent boundary layer separation preceded with a laminar separation bubble. Flow Visualizations were done by using Surface Oil flow Technique for qualitative analysis of the transition zone formed due to the presence of laminar separation bubble As the angle of attack is increased the separation bubble moves towards the leading edge of the airfoil and finally gets shredded or burst at a particular angle of attack resulting in leading edge turbulent flow separation which induces the static stall condition. The flow separation process is critically analyzed and the existence of laminar separation bubble is visualized and quantified with the increase in angle of attack and Re. Effect of Re and angle of attack on the various boundary layer and Separation bubble parameters are obtained and analyzed.

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