Role of laminar separation bubbles in airfoil leading-edge stalls

AIAA Journal ◽  
1981 ◽  
Vol 19 (5) ◽  
pp. 553-556 ◽  
Author(s):  
B. van den Berg
Keyword(s):  
Leading Edge ◽  
Laminar Separation ◽  
Separation Bubbles ◽  
Laminar Separation Bubbles

scholarly journals Characteristics and Effects of Laminar Separation Bubbles on NREL S809 Airfoil Using the γ - R e θ Transition Model

2020 ◽  
Vol 10 (17) ◽  
pp. 6095
Author(s):  
Jang-oh Mo ◽  
Beom-seok Rho
Keyword(s):  
Wind Tunnel ◽  
Wind Turbine ◽  
Leading Edge ◽  
Aerodynamic Performance ◽  
Transition Model ◽  
Clear Understanding ◽  
Airfoil Surface ◽  
Laminar Separation ◽  
Separation Bubbles ◽  
Laminar Separation Bubbles

Understanding the characteristics and effects of the laminar separation bubbles (LSBs) is important in the aerodynamic design of wind turbine airfoils for maximizing wind turbine efficiency. In the present study, numerical simulations using the γ-Reθ transition model were performed to analyze the flow structure of LSBs around a 21% thick NREL S809 airfoil. The simulation results obtained from the γ-Reθ transition model and the standard k-ε model for the aerodynamic coefficients at various angles of attack (AoAs) were compared with the wind tunnel data acquired from the Delft University 1.8 m × 1.25 m low-turbulence wind tunnel. When the AoA increased, the bubble on the suction airfoil surface was found to move closer to the leading edge owing to an earlier laminar separation (LS). Furthermore, the transition onset (TO) points were shown to occur right after separation, thus causing an abrupt increase in turbulence intensity (TI) and forming different bubble extents with increasing AoAs. Consequently, the transition model-based approaches can provide a clear understanding of the characteristics and effects of the LSB on airfoil aerodynamic performance. The findings of this study can provide important insights into redesigning an airfoil with a reduced bubble length causing the improved aerodynamic performance.

Transition mechanisms in laminar separation bubbles with and without incoming wakes and synthetic jet effects

2012 ◽  
Vol 53 (1) ◽  
pp. 173-186 ◽  
Author(s):  
Daniele Simoni ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
Francesco Bertini
Keyword(s):  
Synthetic Jet ◽  
Laminar Separation ◽  
Separation Bubbles ◽  
Laminar Separation Bubbles

Dynamic Stall Flow Structure and Forces on Symmetrical Airfoils at High Angles of Attack and Rotation Rates

2018 ◽  
Vol 141 (5) ◽  
Author(s):  
R. R. Leknys ◽  
M. Arjomandi ◽  
R. M. Kelso ◽  
C. H. Birzer
Keyword(s):  
Flow Structure ◽  
Boundary Layer Separation ◽  
Vortex Structures ◽  
Dynamic Stall ◽  
Aerodynamic Load ◽  
Laminar Separation ◽  
Rotation Rates ◽  
Constant Pitch ◽  
Separation Bubbles ◽  
Laminar Separation Bubbles

This article describes a direct comparison between two symmetrical airfoils undergoing dynamic stall at high, unsteady reduced frequencies under otherwise identical conditions. Particle image velocimetry (PIV) was performed to distinguish the differences in flow structure between a NACA 0021 and a NACA 0012 airfoil undergoing dynamic stall. In addition, surface pressure measurements were performed to evaluate aerodynamic load and investigate the effect of laminar separation bubbles and vortex structures on the pressure fields surrounding the airfoils. Airfoil geometry is shown to have a significant effect on flow structure development and boundary layer separation, with separation occurring earlier for thinner airfoil sections undergoing constant pitch-rate motion. Inertial forces were identified to have a considerable impact on the overall force generation with increasing rotation rate. Force oscillation was observed to correlate with multiple vortex structures shedding at the trailing-edge during high rotation rates. The presence of laminar separation bubbles on the upper and lower surfaces was shown to dramatically influence the steady-state lift of both airfoils. Poststall characteristics are shown to be independent of airfoil geometry such that periodic vortex shedding was observed for all cases. However, the onset of deep stall is delayed with increased nondimensional pitch rate due to the delay in initial dynamic-stall vortex.

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