offshore wind turbine performance assessment using cfd

Offshore wind turbine performance assessment using CFDAhmed Sobhy MaklidAdvisors : Prof. Dr. Mohamed Abbas Kotb Prof. Dr. Adel Abd Elhamlim BanawanFaculty of engineering Alexandria UniversityNaval Architecture & Marine Engineering Department

Presentation Outline Title Slide: backstory OutlineIntroduction/Motivation BackgroundVerification & Validation 2-D case studyFull turbine case studyFSI case studyRelated work Conclusions and Future work

"Live in danger" Nietzsche


IntroductionThe need for alternatives. The potential of wind energy. Government renewable energy plan. (12 % wind by 2020)

Ahmed Sobhy


Why offshore Energy

higher wind speeds and less turbulence( 50% energy )environmental constraintsSubject to technical innovations and revolutionary developments37% reduction in cost for offshore by 2035 vs. 9-10% for onshore wind.

Potential cost savings from 2010 to 2050 by offshore energy sub-areas.


Aims & objectivesAims: Develop a more reliable CFD analysis to investigate the major problems affecting offshore wind turbine reliability (turbine & foundation) hence help in decrease its overall cost.

ObjectivesModel the geometry for both the 2-D case and the 3-D case using CAD programs.Set up the appropriate operating condition for each caseAccurately create the rotating effect of the wind turbine using desktop capabilities.Assess the impact of Performing Verification and validation studiesPerform FSI simulation and calculate the wind load impact on wind turbine blade and offshore foundation.


CFD methodology


Verification & ValidationErrors: deficiencies in a CFD model that are not caused by lack of knowledge

Uncertainty: deficiencies in a CFD model that are caused by lack of knowledge

Verification :" solving the equations right ". Roache (1998)

quantifies the errorsValidation :"solving the right equations". Roache (1998)

quantifies the uncertainty


2-D Airfoil CFD simulationPurpose Optimal Airfoil design and selection.Blade design. (twist)Investigate Verification study impact.Investigate simulation approaches

- 3 cases 3 different approaches DU-82 Aerofoil CFD case 3NREL-S809 Aerofoil CFD case 2Clark-Y Aerofoil CFD case 1


Clark-Y aerofoil CFD simulation

Structured meshR= 1:5R=5L=10 Vin =7.04

Case detailsComputational platformCore I3, 2G RAM Simulation typeSteadyTotal grid size30400Turbulent modelK-omegaAverage CPU time90 min per case


Clark-Y aerofoil Verification pressure Pressure coefficient V&V


Clark-Y aerofoil Validation

O-domain verified caseC-Domain non Verified case Cp at AOA 13



O-domain verified caseC-Domain non Verified case Cp at AOA 16



Lift coefficient Drag coefficient


S-809 aerofoil CFD simulation

Saad IjadStructured meshoutletsymmetryVin =23.8

Case detailsComputational platformCore I3, 2G RAM Simulation typeSteadyTotal grid size24400Turbulent modelK-omegaAverage CPU time90 min per case


NREL S-809 aerofoil results validationLift Coefficient Drag Coefficient


NREL S-809 aerofoil results with DU-82Lift / drag Ratio for DU-82 & NREL S-809


3-D wind turbine CFD simulation

Capture Full turbine blade interactionPower predictionVisualize flow Rotation effect Wake investigationAerodynamic load calculation

NREL-S809 Aerofoil CFD case 2Pressure contoursVelocity vectors


Blind test turbine CFD simulation

outletsymmetryUnstructured meshRotorr =0.45Vin =10m/s

Case detailsComputational platformCore i5, 8G RAMCore i7, 8G RAM Simulation typeSteady, TransientTotal grid size1177802, 2152983Turbulent model k-e ,k- SST average CPU hrs10 hr ,20 hr


Blind test results verification & validationPower Coefficient Thrust Coefficient TSRTSR


wind turbine blade & foundation FSI Investigate structure reliabilityInvestigate Material flexibilityDeformation calculationMoments calculationStresses calculation

investigate efficient blade designs

bladetowerTower & foundation20 m30 m42.3 mVin =1.7 m/sVin =10 m/s


GE-X turbine CFD simulation

outletperiodicVin =12 m/sBladeL=42.3 Mesh refinement

Case detailsComputational platformCore I5, 8G RAM Simulation typeSteady, periodicTotal grid size357311,430142, Turbulent modelk- SST average CPU hrs4: 7 hrs per case


GE-X CFD results verification Optimal TSR


GE-X turbine FEA

Material& fixationImported CFD loadsDeformed bladeEquivalent stressesFE unstructured mesh


load verification against ABS rules

CaseABSCurrent studyerror %Blade10858.790611080 N1.99 %tower(scaled)3.553.33126.69 %foundation(scaled)22.0112.443.6 %Foundation(multiphase)Including all parts148564552466371%


ConclusionCFD RANS-Code ANSYS-Fluent proved to be a useful tool in offshore wind turbine design application ( 2-D, 3-D )Verifications studies can help increase simulation accuracy Similar case approach proved to be very useful in both 2-D and 3-D simulationPresent Turbulent models is suitable for Aerodynamic applicationsFiner mesh does not necessarily improve accuracy only around source of disturbanceCFD results can not be trusted without validation.Common sense verification approach is less time consuming.FSI can be performed using ANSYS CFD + FEA is very powerful tool in blade design


RecommendationsUse more points to describe the aerofoil curve.

Refine the grid around the blade of the blind test case.

Use higher computer and increase the total grid size

Apply smaller time steps to accurately predict flow details

Assign tower & foundation material

Survey appropriate turbulent models for Hydrodynamic applications


Future Work

Study the wake impact of 2 in line wind turbinesInclude nacelle in CFD wake simulationperform a transient 2-way FSI simulationStudy interaction between floating foundation for offshore wind turbines and the wave, wind and current using the multiphase VOF open channel and the JONSWAP or Pierson Moskowitz for fully developed sea. Apply different solution algorithms Apply LES and DES turbulent simulation techniques.Study the Impact of using AIAA (1998) ERCOFTAC (2000) guidelines


References [1]. The New and Renewable Energy Authority, Cairo, Egypt NREA. http://www.nrea.gov.eg/english1.html [2]. www.windpowermonthly.com/article/1317185/onshore-wind-cheaper-coal-nuclear-gas. [3]. Offshore Wind Power Summary Report (TINA) www.lowcarboninnovation.co.uk.[4]. Zahedi A, Current status and future prospects of the wind energy, Conference on Power & Energy, IEEE[5].Introduction to Computational Fluid Dynamics (CFD) University of Iowa, http://css.engineering.uiowa.edu/~fluids.[6] Dan M. Somers, Design and Experimental Results for the S809 Airfoil, National Renewable Energy Laboratory, NREL.[7] Hamid Rahimi, Computational Modeling of Wind Turbines in Open FOAM presentation on the Center for Wind Energy Research Institute of Physics, University of Oldenburg, Germany.[8] Blind test calculations of the performance and wake development for a model wind turbine, Norwegian University of Science and Technology NTNU,[9]. https://confluence.cornell.edu/pages/viewpage.action?pageId=262012971.[47] H K Versteeg and W Malalasekera, An Introduction to Computational Fluid Dynamics THE FINITE VOLUME METHOD Second edition Pearson Education Limited 1995, 2007.