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Research Papers

Enhancement of Free Vortex Filament Method for Aerodynamic Loads on Rotor Blades

[+] Author and Article Information
Hamidreza Abedi

Division of Fluid Dynamics,
Department of Applied Mechanics,
Chalmers University of Technology,
Göteborg SE-412 96, Sweden
e-mail: abedih@chalmers.se

Lars Davidson

Division of Fluid Dynamics,
Department of Applied Mechanics,
Chalmers University of Technology,
Göteborg SE-412 96, Sweden
e-mail: lada@chalmers.se

Spyros Voutsinas

Fluid Section,
School of Mechanical Engineering,
National Technical University of Athens,
Athens 15780, Greece
e-mail: spyros@fluid.mech.ntua.gr

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received February 12, 2016; final manuscript received January 26, 2017; published online March 16, 2017. Assoc. Editor: Douglas Cairns.

J. Sol. Energy Eng 139(3), 031007 (Mar 16, 2017) (12 pages) Paper No: SOL-16-1072; doi: 10.1115/1.4035887 History: Received February 12, 2016; Revised January 26, 2017

The aerodynamics of a wind turbine is governed by the flow around the rotor, where the prediction of air loads on rotor blades in different operational conditions and its relation to rotor structural dynamics is one of the most important challenges in wind turbine rotor blade design. Because of the unsteady flow field around wind turbine blades, prediction of aerodynamic loads with high level of accuracy is difficult and increases the uncertainty of load calculations. An in-house vortex lattice free wake (VLFW) code, based on the inviscid, incompressible, and irrotational flow (potential flow), was developed to study the aerodynamic loads. Since it is based on the potential flow, it cannot be used to predict viscous phenomena such as drag and boundary layer separation. Therefore, it must be coupled to tabulated airfoil data to take the viscosity effects into account. Additionally, a dynamic approach must be introduced to modify the aerodynamic coefficients for unsteady operating conditions. This approach, which is called dynamic stall, adjusts the lift, the drag, and the moment coefficients for each blade element on the basis of the two-dimensional (2D) static airfoil data together with the correction for separated flow. Two different turbines, NREL and MEXICO, are used in the simulations. Predicted normal and tangential forces using the VLFW method are compared with the blade element momentum (BEM) method, the GENUVP code, and the MEXICO wind tunnel measurements. The results show that coupling to the 2D static airfoil data improves the load and power predictions while employing the dynamic stall model to take the time-varying operating conditions into consideration is crucial.

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References

Figures

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Fig. 1

Schematic for the Biot–Savart law

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Fig. 2

Lifting surface and vortex panels construction

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Fig. 3

Schematic of vortex lattice free wake

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Fig. 4

Numbering procedure

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Fig. 5

Schematic of generation and moving of wake panels at each time step

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Fig. 6

Schematic of wake evolution at the first time step

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Fig. 7

Schematic of wake evolution at the second time step

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Fig. 8

Potential load decomposition

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Fig. 9

Viscous load decomposition

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Fig. 10

Radial distribution of blade elements for NREL-5 MW turbine

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Fig. 11

Distribution of angle of attack along the blade for the NREL turbine: (a) case 2, (b) case 6, and (c) case 10; — potential and – – viscous

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Fig. 12

Distribution of tangential force along the blade for the NREL turbine: (a) case 2, (b)case 6, and (c) case 10; — potential and – – viscous

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Fig. 13

Distribution of normal force along the blade for the NREL turbine: (a) case 2, (b) case 6, and (c) case 10; — potential and – – viscous

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Fig. 14

(a) power and (b) thrust curves for the NREL turbine; — VLFW potential, –– VLFW viscous, – – BEM, – ∘ – GENUVP potential, and – × – GENUVP viscous

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Fig. 15

Radial distribution of blade elements for MEXICO turbine

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Fig. 16

Distribution of normal force along the MEXICO turbine's blade, nonyawed flow: (a) case 1, (b) case 2, and (c) case 3, — potential, – – viscous, and ∘ experiment

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Fig. 17

Distribution of tangential force along the MEXICO turbine's blade, nonyawed flow: (a) case 1, (b) case 2 and (c) case 3, — potential, – – viscous, and ∘ experiment

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Fig. 18

Azimuthal variation of (a) tangential and (b) normal forces at 0.25R of radial position, MEXICO turbine, yawed flow, case 1, — potential, – – viscous, – - – dynamic stall, and ∘ experiment

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Fig. 19

Azimuthal variation of (a) tangential and (b) normal forces at 0.35R of radial position, MEXICO turbine, yawed flow, case 1, — potential, – – viscous, – - – dynamic stall, and ∘ experiment

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Fig. 20

Azimuthal variation of (a) tangential and (b) normal forces at 0.60R of radial position, MEXICO turbine, yawed flow, case 1, — potential, – – viscous, – - – dynamic stall, and ∘ experiment

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Fig. 21

Azimuthal variation of (a) tangential and (b) normal forces at 0.82R of radial position, MEXICO turbine, yawed flow, case 1, —: potential, – – viscous, – - – dynamic stall, and ∘ experiment

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Fig. 22

Azimuthal variation of (a) tangential and (b) normal forces at 0.92R of radial position, MEXICO turbine, yawed flow, case 1, — potential, – –: viscous, – - – dynamic stall, and ∘ experiment

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Fig. 23

Hysteresis loop around the stall angle

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Fig. 24

Definition of the lift coefficient parameters in the ONERA model

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Fig. 25

Definition of the drag coefficient parameters in the ONERA model

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