Turbulent boundary layer separation control and loss evaluation of low profile vortex generators

Lengani, Davide; Simoni, Daniele; Ubaldi, Marina; Zunino, Pietro; Bertini, Francesco

doi:10.1016/j.expthermflusci.2011.06.011

Cited by 23 publications

(12 citation statements)

References 22 publications

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“…Similar to a delta wing system (see, eg, Hoerner), a leading edge vortex develops along the vane and is shed near the tip, creating a wake of upwash and downwash regions. This re‐energizes the boundary layer with the outer flow and delays flow reversal (separation) …”

Section: Introductionmentioning

confidence: 99%

Experimental parameter study for passive vortex generators on a 30% thick airfoil

et al. 2018

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Passive vane–type vortex generators (VGs) are commonly used on wind turbine blades to mitigate the effects of flow separation. However, significant uncertainty surrounds VG design guidelines. Understanding the influence of VG parameters on airfoil performance requires a systematic approach targeting wind energy‐specific airfoils. Thus, the 30%‐thick DU97‐W‐300 airfoil was equipped with numerous VG designs, and its performance was evaluated in the Delft University Low Turbulence Wind Tunnel at a chord‐based Reynolds number of 2×106. Oil‐flow visualizations confirmed the suppression of separation as a result of the vortex‐induced mixing. Further investigation of the oil streaks demonstrated a method to determine the vortex strength. The airfoil performance sensitivity to 41 different VG designs was explored by analysing model and wake pressures. The chordwise positioning, array configuration, and vane height were of prime importance. The sensitivity to vane length, inclination angle, vane shape, and array packing density proved secondary. The VGs were also able to delay stall with simulated airfoil surface roughness. The use of the VG mounting strip was detrimental to the airfoil's performance, highlighting the aerodynamic cost of the commonly used mounting technique. Time‐averaged pressure distributions and the lift standard deviation revealed that the presence of VGs increases load fluctuations in the stalling regime, compared with the uncontrolled case.

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Section: Introductionmentioning

confidence: 99%

Experimental parameter study for passive vortex generators on a 30% thick airfoil

et al. 2018

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“…On the other hand, passive flow control method can be executed by adding geometrical discontinuities. The active flow control methods can be suction and/or blowing [6] or high lift devices [7], the passive control methods can be vortex generators [8] or flexibility enhancer [9][10]. Lift can be increased, drag force can be reduced, stall can be delayed, vibrations and noise can be diminished and reattachment of the separated flow can be ensured by means of utilizing these flow control methods.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigation of flow on NACA4412 aerofoil with different aspect ratios

Demir

Özden

Genç

et al. 2016

EPJ Web of Conferences

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Abstract. In this study, the flow over NACA4412 was investigated both numerically and experimentally at a different Reynolds numbers. The experiments were carried out in a low speed wind tunnel with various angles of attack and different Reynolds numbers (25000 and 50000). Airfoil was manufactured using 3D printer with a various aspect ratios (AR = 1 and AR = 3). Smoke-wire and oil flow visualization methods were used to visualize the surface flow patterns. NACA4412 aerofoil was designed by using SOLIDWORKS. The structural grid of numerical model was constructed by ANSYS ICEM CFD meshing software. Furthermore, ANSYS FLUENT TM software was used to perform numerical calculations. The numerical results were compared with experimental results. Bubble formation was shown in CFD streamlines and smoke-wire experiments at z / c = 0.4. Furthermore, bubble shrunk at z / c = 0.2 by reason of the effects of tip vortices in both numerical and experimental studies. Consequently, it was seen that there was a good agreement between numerical and experimental results.

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“…Qualitatively speaking, these modifications promote an increased momentum thickness but reduce the displacement thickness. The shape factor decreases and the skin friction coefficient will increase . It is important to note that these trends may be skewed by the physical presence of the devices, which according to Schubauer and Spangenberg, cause local jumps in δ ∗ and θ that are amplified with the developing boundary layer.…”

Section: Approach and Methodsmentioning

confidence: 98%

“…Drela argues that VGs promote increased dissipation by introducing streamwise vortices into the boundary layer, which consequently increases the sustainable adverse pressure gradient. Lengani et al demonstrated this by analysing the dissipation mechanisms in a separating duct controlled by vane‐type vortex generators. Dissipation in this sense refers to the drain of mean flow kinetic energy through the action of the shear stress with the mean strain rate, essentially, through enhanced mixing.…”

Section: Introductionmentioning

confidence: 99%

An integral boundary layer engineering model for vortex generators implemented in XFOIL

2018

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To assess and optimize vortex generators (VGs) for flow separation control, the effect of these devices should be modelled in a cost and time efficient way. Therefore, it is of interest to extend integral boundary layer models to analyse the effect of VGs on airfoil performance. In this work, the turbulent boundary layer formulation is modified using a source term approach. An additional term is added to the shear-lag equation, to account for the increased dissipation due to streamwise vortex action in the boundary layer, forcing transition at the VG leading edge where applicable. The source term is calibrated and a semi-empirical relation is set up and implemented in XFOIL. The modified code is capable of addressing the effect of the VG height, length, inflow angle, and chordwise position on the airfoil's aerodynamic properties. The predicted polars for airfoils with VGs show a good agreement with reference data, and the code robustness is demonstrated by assessing different airfoil families at a wide range of Reynolds numbers. KEYWORDSintegral boundary layer, separation control, source term, vortex generator, Xfoil INTRODUCTIONFor the next generation of wind turbines, manufacturers aim to design multimegawatt rotors to improve the competitiveness of wind energy technology. To up-scale wind turbines, novel technologies are required and new design challenges will appear. One such aerodynamic challenge is the management of separated flow. Preventing or at least delaying separation over the blades can positively affect the annual energy production (AEP).On top of that, the magnitude and severe variations of the aerodynamic loads associated with separating flows can be reduced, mitigating structural fatigue issues. In the wind energy industry, separation control is often realized by using passive vortex generators (VGs).Vortex generators improve the resistance of a boundary layer against flow separation by re-energizing the flow close to the surface. The streamwise vortices shed from the free tips of the VGs enhance mixing between the high-energy flow in the outer part of the boundary layer with the low-energy regions near the walls (see Schubauer and Spangenberg. 1 ) The physics involved is nontrivial and poses a number of modelling challenges.To achieve a cost-effective scale up of current turbines, it will become necessary to evolve towards a multidisciplinary design process where VGs are already incorporated early in the design phase. To assess and optimize the use of VGs, there will be a need to effectively model these devices in a cost and time efficient manner. BackgroundNumerous VG modelling techniques have been explored in literature, most of which use computational fluid dynamics (CFD). The most direct and intuitive approach is to model the effect of VGs by including them as a local geometrical protrusion in the domain. This approach requires a fully . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...

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Turbulent boundary layer separation control and loss evaluation of low profile vortex generators

Cited by 23 publications

References 22 publications

Experimental parameter study for passive vortex generators on a 30% thick airfoil

Experimental parameter study for passive vortex generators on a 30% thick airfoil

Numerical investigation of flow on NACA4412 aerofoil with different aspect ratios

An integral boundary layer engineering model for vortex generators implemented in XFOIL

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