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.

scholarly journals On the Navier-Stokes Calculation of Separation Bubbles With a New Transition Model

1996 ◽  
Author(s):  
Wolfgang Sanz ◽  
Max F. Platzer
Keyword(s):  
Navier Stokes ◽  
Transition Model ◽  
Compressor Cascade ◽  
Laminar Separation ◽  
Turbulent Transition ◽  
Separation Bubbles ◽  
Turbomachinery Blades ◽  
Naca 0012 ◽  
Onset Location ◽  
Laminar Separation Bubbles

Laminar separation bubbles are commonly observed on turbomachinery blades and therefore require effective methods for their prediction. Therefore, a newly developed transition model by Gostelow et al. (1995) is incorporated into an upwind-biased Navier-Stokes code to simulate laminar-turbulent transition in the boundary layer. A study of the influence of the two adjustable parameters of the model, the transition onset location and the spot generation rate, is conducted and it is found that it can predict laminar separation bubbles, measured on a NACA 0012 airfoil. Additional results are presented for separation bubbles in an annular compressor cascade.

Numerical Simulation of Influence with Surface Contamination on Aerodynamic Performance of Dedicated Wind Turbine Airfoil

2013 ◽  
Vol 724-725 ◽  
pp. 572-575
Author(s):  
Pan Wu ◽  
Chun Li ◽  
Zhi Min Li
Keyword(s):  
Numerical Simulation ◽  
Wind Turbine ◽  
Leading Edge ◽  
Aerodynamic Performance ◽  
Surface Contamination ◽  
Suction Surface ◽  
Airfoil Surface ◽  
Pressure Surface ◽  
Sst Turbulence Model ◽  
Wind Turbine Airfoil

A Numerical simulation on the influence of airfoil surface contamination on the aerodynamic performance of wind turbines was performed. It chose the dedicated wind turbine airfoil as the research object. The k-ω Shear Stress Transmission (SST) turbulence model was selected for CFD calculation. The roughness height which arranged evenly on the airfoil was changed from 0.03mm to 2.0mm to obtain the sensitive roughness. The airfoil was divided into 18 sections for analyzing the effect on the lift & the drag coefficient, due to various locations of sensitive roughness. By comparing the result computed by XFOIL and CFD calculation, it can be known this airfoils sensitive locations in suction surface and pressure surface. The sensitive locations in suction surface were 53% and 92% from the chord line towards the leading edge, while 44% and 88% in pressure surface. The sensitive roughness in sensitive locations delayed the location of the transition point.

scholarly journals Active Control of Laminar Separation: Simulations, Wind Tunnel, and Free-Flight Experiments

Aerospace ◽  
2018 ◽  
Vol 5 (4) ◽  
pp. 114 ◽  
Author(s):  
Andreas Gross ◽  
Hermann Fasel
Keyword(s):  
Wind Tunnel ◽  
Active Control ◽  
Active Flow Control ◽  
Reynolds Numbers ◽  
Scale Model ◽  
Separation Control ◽  
Free Flight ◽  
Laminar Separation ◽  
Separation Bubbles ◽  
Laminar Separation Bubbles

When a laminar boundary layer is subjected to an adverse pressure gradient, laminar separation bubbles can occur. At low Reynolds numbers, the bubble size can be substantial, and the aerodynamic performance can be reduced considerably. At higher Reynolds numbers, the bubble bursting can determine the stall characteristics. For either setting, an active control that suppresses or delays laminar separation is desirable. A combined numerical and experimental approach was taken for investigating active flow control and its interplay with separation and transition for laminar separation bubbles for chord-based Reynolds numbers of Re ≈ 64,200–320,000. Experiments were carried out both in the wind tunnel and in free flight using an instrumented 1:5 scale model of the Aeromot 200S, which has a modified NACA 643-618 airfoil. The same airfoil was also used in the simulations and wind tunnel experiments. For a wide angle of attack range below stall, the flow separates laminar from the suction surface. Separation control via a dielectric barrier discharge plasma actuator and unsteady blowing through holes were investigated. For a properly chosen actuation amplitude and frequency, the Kelvin–Helmholtz instability results in strong disturbance amplification and a “roll-up” of the separated shear layer. As a result, an efficient and effective laminar separation control is realized.

On the Numerical Difficulties in Calculating Laminar Separation Bubbles

2002 ◽  
Author(s):  
Wolfgang Sanz ◽  
Max F. Platzer
Keyword(s):  
Numerical Study ◽  
Separation Bubble ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Separated Flow ◽  
Transition Model ◽  
Laminar Separation ◽  
Separation Bubbles ◽  
Transition Models ◽  
Laminar Separation Bubbles

Behaviour of laminar separation bubbles on the surfaces of compressor and turbine blades has increasingly attracted the attention of researchers and designers of turbomachinery in the last years. For the numerical investigation of laminar separation bubbles transition models are implemented into Navier-Stokes flow solvers to predict their location, extent and behaviour accurately. Several researchers conducted comparative studies to investigate the applicability of different transition models for separated-flow transition. In this work a comprehensive numerical study is carried out to investigate not only the influence of the transition model, but of the solution method in general on laminar separation bubble prediction. The flow around a NACA 0012 airfoil at different angles of attack where laminar separation bubbles were observed in experiments is chosen as test case. Different flow solvers (Osher and Roe scheme), different turbulence models as well as different solution procedures were applied together with transition models. The results show that besides the transition model other parameters like the discretisation scheme of the turbulence model or the flow solver have a comparably large influence on the computational result.

On the Navier–Stokes Calculation of Separation Bubbles With a New Transition Model

1998 ◽  
Vol 120 (1) ◽  
pp. 36-42 ◽  
Author(s):  
W. Sanz ◽  
M. F. Platzer
Keyword(s):  
Navier Stokes ◽  
Transition Model ◽  
Compressor Cascade ◽  
Laminar Separation ◽  
Turbulent Transition ◽  
Separation Bubbles ◽  
Turbomachinery Blades ◽  
Naca 0012 ◽  
Onset Location ◽  
Laminar Separation Bubbles

Laminar separation bubbles are commonly observed on turbomachinery blades and therefore require effective methods for their prediction. Therefore, a newly developed transition model by Gostelow et al. (1996) is incorporated into an upwind-biased Navier–Stokes code to simulate laminar—turbulent transition in the boundary layer. A study of the influence of the two adjustable parameters of the model, the transition onset location and the spot generation rate, is conducted and it is found that it can predict laminar separation bubbles, measured on a NACA 0012 airfoil. Additional results are presented for separation bubbles in an annular compressor cascade.

Experimental investigations of flow over NACA airfoils 0021 and 4412 of wind turbine blades with and without Tubercles

2021 ◽  
pp. 0309524X2110071
Author(s):  
Usman Butt ◽  
Shafqat Hussain ◽  
Stephan Schacht ◽  
Uwe Ritschel
Keyword(s):  
Wind Tunnel ◽  
Drag Coefficient ◽  
Wind Turbine ◽  
Critical Region ◽  
Lift Coefficient ◽  
Turbine Blades ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Experimental Investigations ◽  
Wind Turbine Blades

Experimental investigations of wind turbine blades having NACA airfoils 0021 and 4412 with and without tubercles on the leading edge have been performed in a wind tunnel. It was found that the lift coefficient of the airfoil 0021 with tubercles was higher at Re = 1.2×105 and 1.69×105 in post critical region (at higher angle of attach) than airfoils without tubercles but this difference relatively diminished at higher Reynolds numbers and beyond indicating that there is no effect on the lift coefficients of airfoils with tubercles at higher Reynolds numbers whereas drag coefficient remains unchanged. It is noted that at Re = 1.69×105, the lift coefficient of airfoil without tubercles drops from 0.96 to 0.42 as the angle of attack increases from 15° to 20° which is about 56% and the corresponding values of lift coefficient for airfoil with tubercles are 0.86 and 0.7 at respective angles with18% drop.

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