Validation of 3D CFD Simulations of Downwind NREL Wind Turbine using CFD code OpenFOAM.

University essay from KTH/Energiteknik

Abstract:

This thesis project is inside a Fraunhofer institute of Wind Energy and Energy System Technology (IWES) downwind turbine project which is three-dimensional (3D) unsteady aerodynamics experiment of horizontal axis wind turbine of phase VI baseline case of NREL (National Renewable Energy Laboratory-USA) and part of WP4 experiment of IEA (International Energy Agency) task number 29. The objective of this thesis project is to validate the simulations of downwind turbine using CFD (computational fluid dynamics) code OpenFOAM (open source field operation and manipulation). The turbine with tower and nacelle is to be simulated using RANS and URANS (Unsteady Reynolds-averaged Navier-Stokes). GGI (General Grid Interface) is used to integrate rotating mesh with stationary mesh. Detailed CAD modeling of blade (aerofoil NREL S809), nacelle, hub and tower of wind turbine has been developed using Autodesk Inventor Professional and CATIAV5. Refined surface hybrid mesh is generated through STL (STereoLithography) surface files using OpenFOAM pre-processing utilities, blockMesh and snappyHexMesh respectively. Cases for Steady simulations using GGI as a interface to integrate moving mesh with stationary is prepared using OpenFOAM dictionaries and libraries. Results from steady simulation are mapped on transient simulation using GGI as an interface. Steady and unsteady simulations are investigated using OpenFOAM standard numerical solvers MRFSimpleFOAM and pimpleDymFOAM respectively. A 3rd party software ParaView 4.0.1 is used which a graphical interface for visualizing and comparing the results obtained from conducted CFD simulations using OpenFOAM toolbox. Local Angle of attack, Axial Induction factor, relative velocity, components of normal and tangential forces are calculated for 3D rotating blade using post processing utilities within OpenFOAM toolbox and ParaView. Results are compared and validated with experimental data. Discussion about 3D tower-blade interaction, rotational effects, boundary layer transitions and stall phenomenon has been done within this research work. 

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