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Numerical Study on Performance of Innovative Wind Turbine Blade for Loads Reduction

Numerical Study on Performance of Innovative Wind Turbine Blade for Loads Reduction. T. Maggio 1 , F. Grasso 2 , D.P. Coiro 1 1) Università degli Studi di Napoli “Federico II”, 2) Energy research Centre of the Netherlands. EWEC 2011, 14-17 March, Brussels, Belgium. Table of Contents.

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Numerical Study on Performance of Innovative Wind Turbine Blade for Loads Reduction

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  1. Numerical Study on Performance of Innovative Wind Turbine Blade for Loads Reduction T. Maggio1, F. Grasso2, D.P. Coiro1 1) Università degli Studi di Napoli “Federico II”, 2) Energy research Centre of the Netherlands EWEC 2011, 14-17 March, Brussels, Belgium

  2. Table of Contents • Objectives • Overview of AWSM code • Geometrical deformation extension • Swept blade investigation • Conclusions

  3. Objectives • This work is focused on a numerical investigation about the benefits of swept blades in terms of noise and load reductions. • Extension of AWSM code in order to take into account the deformation of the blade due to the torsion and bending moments.

  4. Overview of AWSM* Code *designed at ECN by Arne van Garrel van Garrel, A., “Development of a Wind Turbine Aerodynamics Simulation Module”, ECN, ECN-C-03-079, Petten, the Netherlands, 2003.

  5. Overview of AWSM code (1/4) Aerodynamic Windturbine Simulation Module (AWSM) Main Features • Numerical code based on the Generalized Prandtl’s Lifting Line Theory • Airfoil’s viscous characteristics taken into account • Analysis of multi-body configurations • General-shape geometries can be assigned (non planar and non conventional configurations: winglets, curved blades…) • Steady and unsteady analysis • Analysis in yaw, pitch misalignments and non uniform wind (wind shear) conditions • Ground effect implemented • Induced velocity calculations in the external field • Aeroelastic simulations coupling capabilities 5 27-8-2014

  6. Overview of AWSM code (2/4) Lifting Line Method – Flowfield model The effects of viscosity are taken into account through the user-supplied nonlinear relationshipbetween local flow direction and local lift , drag and pitching moment coefficients.

  7. Overview of AWSM code (3/4) Do i=1,Ntimestep Do j=1, Nequilibrium Check convergence Calculate forces Call applygeomsnapshot Call uvwcpointwind End do End do How AWSM Works OUTPUT FILES INPUT FILES AWSM • CommandLine input • Geom file geometry specification • AeroData file aerodynamic coefficients database • AeroLink file linking geometry to aerodynamic tables • WindScenario fileprescribing wind velocities • AeroResults file:aerodynamic performance • GeomResults file: geometry specification about the blade and the wake

  8. Overview of AWSM code (4/4) NASA Ames data *results from: Grasso, F. van Garrel, A., Schepers, G., “Development and Validation of Generalized Lifting Line Based Code for Wind Turbine Aerodynamics”, AIAA, 49° AIAA Aerospace Sciences Meeting, Orlando Florida, USA, 4-7 January 2011.

  9. Geometrical Deformation Extension

  10. Geometrical deformation extension (1/5) Blade Deformation In the reality the blade is not a rigid body but subject to deformations • Out of plane bending • In plane bending • Torsion In the present work, only out of plane bending and torsion are taken into account

  11. Geometrical deformation extension (2/5) Blade Equations of Motion Bending out of plane Ut Hinge equivalent beam Up Twist Hinge equivalent beam

  12. Geometrical deformation extension (3/5) Mass moment of inertiaw.r.t. out of plane bending axis Static moment of inertia Nondimensionalhinge offset The effectsdue to the yawrate and crosswind are neglected Out of plane bending stiffness Flapping moment due to the aerodynamicforces Mass moment of inertiaw.r.t. pitchaxis Torsionstiffness Damping factor • The bending mode is uncoupled from the torsion. • The equations are solved by using 4th order Runge Kutta Torsion moment due to the aerodynamic moment and forces

  13. Geometrical deformation extension (4/5) θknown βknown rotationcentre New leadingedge and trailingedgecoordinates New valueof the componentofwindspeedcalculate at controlpoint Update the geometry (applygeomsnapshot) Update windspeed ( uvwcPointWind) New AWSM perform

  14. Geometrical deformation extension (5/5) AWSM Implementation OUTPUT FILES INPUT FILES AWSM • AeroResults file • GeomResultsfile • CommandLine input • Geom file • AeroData file • AeroLink file • WindScenario file Do i=1,Ntimestep Do j=1, Nequilibrium Check convergence Calculateforces Callrunge_torsion Callrunge_bending Callapplygeomsnapshot Calluvwcpointwind End do End do • Additional Input • Massbladeproperty • Curvature (∆x) • Loss factor • Torsionalfrequency • Non rotating and rotating bending frequency

  15. Numerical Investigation on Swept Blades 15 27-8-2014

  16. Numerical investigation on swept blades (1/5) UpWind project

  17. Numerical investigation on swept blades (2/5) Lift coefficient distribution along the blade First blade - Last time step - Free wake (3 free rotations) – 10 degangular step without geometrical extension with geometrical extension no shear, no ground wind speed: 8 m/s omega: 0.964 rad/s no shear, no ground wind speed: 8 m/s omega: 0.964 rad/s torsional frequency: 10.5p bending frequency: 4.3p

  18. Numerical investigation on swept blades (3/5) Parametricinvestigation

  19. Numerical investigation on swept blades (4/5) Parametricinvestigation Lift coefficient distribution along the blade By using an aft swept blade, the loads on the blade decrease; as consequence, a power loss of 10% for the curve blade and of 3% for the curve blade1 is obtained. Using the fore swept blade (curve blade2) can be seen an increment of loads and thrust. This leads to an increase in tower loads, requiring a stiffer and more expensive structure.

  20. Numerical investigation on swept blades (5/5) Parametricinvestigation Lift coefficientas time changes at 92% blade radius in presence of a gust The gust is modeled according to the international standards IEC 61400 with a wind speed of 11 m/s. no shear, no ground wind speed: 11 m/s omega: 1.246 rad/s torsion frequency: 10.5p bending frequency: 4.3p The results clearly show that by adopting an aft-swept blade, a significant reduction in load fluctuation and so in fatigue, can be achieved

  21. Conclusions • In order to investigate the performances of aft-swept blades, a code based on the lifting line theory and coupled with a free wake method has been used. • AWSM has been extended in order to take into account the dynamic deformation of the geometry due to the aerodynamic forces acting on the blades. • A first parametric investigation has been performed by comparing the performances of blades with different curvatures. • Because of the reduction in local angle of attack along the blade, a sensitive reduction in noise is expected. Detailed analyses are in schedule.

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