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

Baldacchino, Daniel; Ferreira, Carlos; Tavernier, Delphine De; Timmer, W.A.; Bussel, G.J.W. Van

doi:10.1002/we.2191

Cited by 84 publications

(73 citation statements)

References 29 publications

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“…Therefore, this study puts emphasis on the effects of chordwise VG position xVG and vane height h on the unsteady aerodynamic responses of the airfoil undergoing pitch oscillations. The airfoil chord length c is 650 mm and the geometric vane inflow angle β is ±15°, which is entirely consistent with recent wind tunnel experiments [11]. Table 1 gives the parameters of VG sets in this work, including the double-row VGs at 20% and 40% chordwise locations.…”

Section: Geometry and Mesh Generationsupporting

confidence: 81%

Numerical Investigation of Passive Vortex Generators on a Wind Turbine Airfoil Undergoing Pitch Oscillations

Zhu

Wang

2019

Energies

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Passive vortex generators (VGs) are widely used to suppress the flow separation of wind turbine blades, and hence, to improve rotor performance. VGs have been extensively investigated on stationary airfoils; however, their influence on unsteady airfoil flow remains unclear. Thus, we evaluated the unsteady aerodynamic responses of the DU-97-W300 airfoil with and without VGs undergoing pitch oscillations, which is a typical motion of the turbine unsteady operating conditions. The airfoil flow is simulated by numerically solving the unsteady Reynolds-averaged Navier-Stokes equations with fully resolved VGs. Numerical modelling is validated by good agreement between the calculated and experimental data with respect to the unsteady-uncontrolled flow under pitch oscillations, and the steady-controlled flow with VGs. The dynamic stall of the airfoil was found to be effectively suppressed by VGs. The lift hysteresis intensity is greatly decreased, i.e., by 72.7%, at moderate unsteadiness, and its sensitivity to the reduced frequency is favorably reduced. The influences of vane height and chordwise installation are investigated on the unsteady aerodynamic responses as well. In a no-stall flow regime, decreasing vane height and positioning VGs further downstream can lead to relatively high effectiveness. Compared with the baseline VG geometry, the smaller VGs can decrease the decay exponent of nondimensionalized peak vorticity by almost 0.02, and installation further downstream can increase the aerodynamic pitch damping by 0.0278. The obtained results are helpful to understand the dynamic stall control by means of conventional VGs and to develop more effective VG designs for both steady and unsteady wind turbine airfoil flow.

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Section: Geometry and Mesh Generationsupporting

confidence: 81%

Numerical Investigation of Passive Vortex Generators on a Wind Turbine Airfoil Undergoing Pitch Oscillations

Zhu

Wang

2019

Energies

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“…In Figure A and B, reference polars and XFOIL calculations for various VG positions are presented. The reference data were obtained by Baldacchino et al on a DU97W300 airfoil model with 0.65‐m chord at a Reynolds number of 2×10 6 in free transition. The model was equipped with counter‐rotating Delta‐shaped VGs with a height of 10 mm and length of 3 h V G , set under an inflow angle of 15°.…”

Section: Resultsmentioning

confidence: 99%

“…Oil‐flow visualizations of the DU97W300 airfoil depicting the (suction side) advance of the transition region ahead of the VG array with angle of attack (images obtained from the campaign described in Baldacchino et al) [Colour figure can be viewed at wileyonlinelibrary.com]…”

Section: Approach and Methodsmentioning

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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“…Passive or active flow control strategies are promising technologies to favorably influence the boundary layer. Passive solutions to mention are vortex generators (Baldacchino et al, 2018) that introduce kinetic energy into the boundary or Gurney flaps and spoilers that redirect the flow by altering the Kutta condition. More sophisticated active systems featuring, for example, tangential blowing (Seifert et al, 1993;McCormick, 2000) or injecting momentum by plasma actuators (Post and Corke, 2004) allow for specific control strategies without generating selfdrag or noise of the device.…”

Section: Improvement Of the Aerodynamic Efficiency In The Blade Root mentioning

confidence: 99%

Numerical analyses and optimizations on the flow in the nacelle region of a wind turbine

et al. 2018

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Abstract. The present study investigates flow dynamics in the hub region of a wind turbine focusing on the influence of nacelle geometry on the root aerodynamics by means of Reynolds averaged Navier-Stokes simulations with the code FLOWer. The turbine considered is a generic version of the Enercon E44 converter incorporating blades with flat-back-profiled root sections. First, a comparison is drawn between an isolated rotor assumption and a setup including the baseline nacelle geometry in order to elaborate the basic flow features of the blade root. It was found that the nacelle reduces the trailed circulation of the root vortices and improves aerodynamic efficiency for the inner portion of the rotor; on the other hand, it induces a complex vortex system at the juncture to the blade that causes flow separation. The origin of these effects is analyzed in detail. In a second step, the effects of basic geometric parameters describing the nacelle have been analyzed with the purpose of increasing the aerodynamic efficiency in the root region. Therefore, three modification categories have been addressed: the first alters the nacelle diameter, the second varies the blade position relative to the nacelle and the third comprises modifications in the vicinity of the blade-nacelle junction. The impact of the geometrical modifications on the local flow physics are discussed and assessed with respect to aerodynamic performance in the blade root region. It was found that increasing the nacelle diameter deteriorates the root aerodynamics, since the flow separation becomes more pronounced. Possible solutions identified to reduce the flow separation are a shift of the blade in the direction of the rotation or the installation of a fairing fillet in the junction between the blade and the nacelle.

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

Cited by 84 publications

References 29 publications

Numerical Investigation of Passive Vortex Generators on a Wind Turbine Airfoil Undergoing Pitch Oscillations

Numerical Investigation of Passive Vortex Generators on a Wind Turbine Airfoil Undergoing Pitch Oscillations

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

Numerical analyses and optimizations on the flow in the nacelle region of a wind turbine

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