Réthoré, Pierre-Elouan

Sørensen, Niels N.

Troldborg, Niels

Zahle, Frederik

Online Research Database In Technology

                       General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.  • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal   If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.     Downloaded from orbit.dtu.dk on: Dec 20, 2017Comparison of wind turbine wake properties in non-uniform inflow predicted bydifferent CFD rotor modelsTroldborg, Niels; Zahle, Frederik; Sørensen, Niels N.; Réthoré, Pierre-ElouanPublication date:2012Link back to DTU OrbitCitation (APA):Troldborg, N., Zahle, F., Sørensen, N. N., & Réthoré, P-E. (2012). Comparison of wind turbine wake propertiesin non-uniform inflow predicted by different CFD rotor models [Sound/Visual production (digital)]. The science ofMaking Torque from Wind 2012, Oldenburg, Germany, 09/10/2012, http://www.forwind.de/makingtorqueComparison of wind turbine wake properties in non-uniform inflow predicted by different CFD rotor models Niels Troldborg, Frederik Zahle, Niels N. Sørensen, Pierre-Elouan Réthoré   Wind Energy Department, DTU Wind Energy, DK-4000 Roskilde,  Denmark October 9-11, Oldenburg, Germany Torque 2012 2 DTU Wind Energy  Background Wind turbine models in CFD • Fully resolved rotor (FR) • Actuator line model (AL) • Actuator disc model (AD) October 9-11, Oldenburg, Germany Torque 2012 3 DTU Wind Energy  Background  The blade/airfoil boundary layer is resolved  The required number of grid points for one rotor using RANS is O(107)  Provides detailed insight about flow behaviour  Usually used for accurately predict loads and power production  Too computationally heavy for several wind turbines.  Wind turbine models in CFD • Fully resolved rotor (FR) • Actuator line model (AL) • Actuator disc model (AD) October 9-11, Oldenburg, Germany Torque 2012 4 DTU Wind Energy  Background  Blades represented as lines. Wind turbine models in CFD • Fully resolved rotor (FR) • Actuator line model (AL) • Actuator disc model (AD) October 9-11, Oldenburg, Germany Torque 2012 5 DTU Wind Energy  Background  Blades represented as lines.  Aerodynamic blade forces determined from 2D airfoil data. Wind turbine models in CFD • Fully resolved rotor (FR) • Actuator line model (AL) • Actuator disc model (AD) October 9-11, Oldenburg, Germany Torque 2012 6 DTU Wind Energy  Background  Blades represented as lines.  Aerodynamic blade forces determined from 2D airfoil data.   )(tan 1VrVzDDLLrel CCcVDLeef)()(221Wind turbine models in CFD • Fully resolved rotor (FR) • Actuator line model (AL) • Actuator disc model (AD) October 9-11, Oldenburg, Germany Torque 2012 7 DTU Wind Energy  Background  Blades represented as lines.  Aerodynamic blade forces determined from 2D airfoil data.  Blade forces smeared to avoid singular behaviour.  222/33exp1, dffDDLLrel CCcVDLeef)()(221  )(tan 1VrVzWind turbine models in CFD • Fully resolved rotor (FR) • Actuator line model (AL) • Actuator disc model (AD) October 9-11, Oldenburg, Germany Torque 2012 8 DTU Wind Energy  Background Advantages:  Low number of grid points O(106) needed compared to full rotor CFD.  Applicable with simple grid geometries.  Captures the most important features of the wake including tip/root vortices.  Well suited for LES simulations (no boundary layers need to be resolved)  Disadvantages:  Relies on airfoil data  Wind turbine models in CFD • Fully resolved rotor (FR) • Actuator line model (AL) • Actuator disc model (AD) October 9-11, Oldenburg, Germany Torque 2012 9 DTU Wind Energy  Background  Rotor represented by forces distributed on permeable disc.  Wind turbine models in CFD • Fully resolved rotor (FR) • Actuator line model (AL) • Actuator disc model (AD) October 9-11, Oldenburg, Germany Torque 2012 10 DTU Wind Energy  Background  Rotor represented by forces distributed on permeable disc.   The disc loading is either prescribed or determined from airfoil data.  Pressure velocity decoupling avoided using Gaussian force smearing or a modified Rhie-Chow algorithm Wind turbine models in CFD • Fully resolved rotor (FR) • Actuator line model (AL) • Actuator disc model (AD) October 9-11, Oldenburg, Germany Torque 2012 11 DTU Wind Energy  Background Axial velocity contours and streamlines for a uniformly loaded disc at CT=0.89 Advantages:  Low number of grid points  Applicable with simple grid geometries  Well suited for LES simulations  Large time steps can be used  Can run in steady state  Disadvantages:  Relies on airfoil data  Does not capture influence of individual blades  May be questionable in non-uniform inflow  Wind turbine models in CFD • Fully resolved rotor (FR) • Actuator line model (AL) • Actuator disc model (AD) October 9-11, Oldenburg, Germany Torque 2012 12 DTU Wind Energy  Background Summary:  AL/AD typically used for wake studies   Details of rotor geometry assumed unimportant in far wake  Objectives: Study importance of wind turbine model on wake characteristics   How much details are lost due to the simpler models?   Conduct a consistent comparison of the three models   Same numerical setup for all models    October 9-11, Oldenburg, Germany Torque 2012 13 DTU Wind Energy  Previous work Simulations of NREL 5MW reference turbine in non-sheared laminar inflow Axial velocity  Wake of FR develops faster into a bell shaped form than the AL and AD.  Faster spreading of wake is caused by larger TKE in the FR simulation. Snapshot of vorticity magnitude contours in horizontal cross-section through rotor center.   FR AL AD October 9-11, Oldenburg, Germany Torque 2012 14 DTU Wind Energy  Previous work Simulations of NREL 5MW reference turbine in non-sheared turbulent inflow Snapshot of vorticity magnitude contours in horizontal cross-section through rotor center.   Axial velocity FR AL AD October 9-11, Oldenburg, Germany Torque 2012 15 DTU Wind Energy  Present work Objectives: Study importance of wind turbine model on wake characteristics in non-uniform inflow:  Sheared inflow  Yawed inflow   Simulating the 2MW NM80 turbine using similar numerical setup October 9-11, Oldenburg, Germany Torque 2012 16 DTU Wind Energy  Approach – Flow solver EllipSys3D:  In-house CFD code  Incompressible Navier-Stokes equations  Finite volume discretization  Structured curvelinear grids  Pressure/Velocity formulation  Multigrid  Multiblock  Grid sequencing   MPI Solver parameters:  QUICK/QUICK_CDS4  SIMPLE   DES October 9-11, Oldenburg, Germany Torque 2012 17 DTU Wind Energy  Approach - Numerical setup Background mesh:  Same background mesh for all simulations   Half cylinder with radius 8D  308 blocks of 323 (10.1 ∙106 cells)  High resolution of the first 5D of the wake (cell size 1.3m x 1.3m x 0.8m) October 9-11, Oldenburg, Germany Torque 2012 18 DTU Wind Energy  Approach - Numerical setup Full rotor with overset grid:  Four overlapping mesh groups   Rotor mesh generated using HypGrid3D to form an O-O topology  Total number of grid points is 26.7∙106   Rotor surface with a non-slip boundary condition  First cell height y=1.0∙106 (y+ < 2) October 9-11, Oldenburg, Germany Torque 2012 19 DTU Wind Energy  Approach - Numerical setup Actuator line simulations:  Same background mesh as the full rotor simulation (10.1 ∙106 cells)  Force smearing using 3D convolution  33 force elements along each line October 9-11, Oldenburg, Germany Torque 2012 20 DTU Wind Energy  Approach - Numerical setup Actuator disc simulations:  Same background mesh as the full rotor simulation (10.1 ∙106 cells)  33 radial force elements  Force smearing using 1D convolution in normal and radial direction  Forces on each differential area dA=rdrdθ is determined from local flow conditions and airfoil data.  October 9-11, Oldenburg, Germany Torque 2012 21 DTU Wind Energy  Results Test cases • Sheared inflow  • Yawed inflow October 9-11, Oldenburg, Germany Torque 2012 22 DTU Wind Energy  Results  V∞ = 8 m/s  Power law inflow (α = 0.55):    Test cases • Sheared inflow  • Yawed inflow  HyVVZOctober 9-11, Oldenburg, Germany Torque 2012 23 DTU Wind Energy  Results  Normal loads in good agreement  Tangential loads less in FR than in AL and AD    Test cases • Sheared inflow  • Yawed inflow FR AL  AD Spanwise distribution of normal and tangential loads at various azimuth positions October 9-11, Oldenburg, Germany Torque 2012 24 DTU Wind Energy  Results  Vorticity from tip vortices much stronger in FR than in AL and AD.   Wake of FR more unstable  Similar vorticity contours for AL and AD (except for instabilty in the far wake)  Reasons for more unstable wake of FR:  Higher grid resolution  Fluctuating loads (e.g. stall effets near root) Snapshot of vorticity magnitude contours in horizontal cross-section through rotor center.   Test cases • Sheared inflow  • Yawed inflow FR AL AD October 9-11, Oldenburg, Germany Torque 2012 25 DTU Wind Energy  Results Test cases • Sheared inflow  • Yawed inflow  Good agreement in predicted near wake deficit  AL and AD in close agreement  Wake of FR develops faster into a bell shaped form than the AL and AD. AL AD Streamwise velocity contours in cross-section 1D downstream.   Mean streamwise velocity 1D downstream for various azimuth positions FR AL  AD FR 1D October 9-11, Oldenburg, Germany Torque 2012 26 DTU Wind Energy  Results Test cases • Sheared inflow  • Yawed inflow  Good agreement in predicted near wake deficit  AL and AD in close agreement  Wake of FR develops faster into a bell shaped form than the AL and AD. FR AL AD Streamwise velocity contours in cross-section 3D downstream.   Mean streamwise velocity 3D downstream for various azimuth positions FR AL  AD 3D October 9-11, Oldenburg, Germany Torque 2012 27 DTU Wind Energy  Results Test cases • Sheared inflow  • Yawed inflow  Good agreement in predicted near wake deficit  AL and AD in close agreement  Wake of FR develops faster into a bell shaped form than the AL and AD. FR AL AD Streamwise velocity contours in cross-section 5D downstream.   Mean streamwise velocity 5D downstream for various azimuth positions FR AL  AD 5D October 9-11, Oldenburg, Germany Torque 2012 28 DTU Wind Energy  Results Test cases • Sheared inflow  • Yawed inflow  V∞ = 8 m/s  Yaw error of 20° October 9-11, Oldenburg, Germany Torque 2012 29 DTU Wind Energy  Results Test cases • Sheared inflow  • Yawed inflow  Load predictions in good agreement Spanwise distribution of normal and tangential loads at various azimuth positions AL  AD October 9-11, Oldenburg, Germany Torque 2012 30 DTU Wind Energy  Results Test cases • Sheared inflow  • Yawed inflow  Similar vorticity contours Snapshot of vorticity magnitude contours in horizontal cross-section through rotor center.   AL AD October 9-11, Oldenburg, Germany Torque 2012 31 DTU Wind Energy  Results Test cases • Sheared inflow  • Yawed inflow  Good agreement in predicted wake deficit and wake structure Vorticity magnitude contours in cross-section 1D downstream.   Mean streamwise velocity 1D downstream for various azimuth positions AL  AD 1D AL AD October 9-11, Oldenburg, Germany Torque 2012 32 DTU Wind Energy  Results Test cases • Sheared inflow  • Yawed inflow Mean streamwise velocity 3D downstream for various azimuth positions  Good agreement in predicted wake deficit and wake structure Vorticity magnitude contours in cross-section 3D downstream.   AL  AD 3D AL AD October 9-11, Oldenburg, Germany Torque 2012 33 DTU Wind Energy  Results Test cases • Sheared inflow  • Yawed inflow Mean streamwise velocity 5D downstream for various azimuth positions  Good agreement in predicted wake deficit and wake structure Vorticity magnitude contours in cross-section 5D downstream.   AL  AD 5D AL AD October 9-11, Oldenburg, Germany Torque 2012 34 DTU Wind Energy  Conclusions  Sheared inflow  Three models show good agreement in axial velocity up to 2D downstream of the turbine.  Further downstream the FR simulation predicts a faster smearing of the mean gradients  Much higher turbulence in the FR simulation  Generally good agreement between AL and AD for all downstream position.   Yawed inflow  Good resemblance between wake behavior predicted using AL and AD.  AD representation as accurate as AL even in non-uniform inflow. 

Comparison of wind turbine wake properties in non-uniform inflow predicted by different CFD rotor models

http://orbit.dtu.dk/ws/files/51497697/Comparison_of_wind_turbine_wake_properties.pdf

Comparison of wind turbine wake properties in non-uniform inflow predicted by different CFD rotor models

Abstract

Similar works

Full text

Available Versions

Online Research Database In Technology