FAST.Farm User’s Guide and Theory Manual - NREL

1 nrel is a national laboratory of the Department of Energy Office of Energy Efficiency & Renewable Energy Operated by the Alliance for Sustainable Energy, LLC This report is available at no cost from the National Renewable Energy Laboratory ( nrel ) at Contract No. DE-AC36-08GO28308 Technical Report nrel /TP-5000-78485 April 2021 User s Guide and Theory Manual Jason Jonkman and Kelsey Shaler National Renewable Energy Laboratory nrel is a national laboratory of the Department of Energy Office of Energy Efficiency & Renewable Energy Operated by the Alliance for Sustainable Energy, LLC This report is available at no cost from the National Renewable Energy Laboratory ( nrel ) at Contract No. DE-AC36-08GO28308 National Renewable Energy Laboratory 15013 Denver West Parkway Golden, CO 80401 303-275-3000 Technical Report nrel /TP-5000-78485 April 2021 User s Guide and Theory Manual Jason Jonkman and Kelsey Shaler National Renewable Energy Laboratory Suggested Citation Jonkman, Jason, and Kelsey Shaler.

2 2021. User s Guide and Theory Manual . Golden, CO: National Renewable Energy Laboratory. nrel /TP-5000-78785. NOTICE This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided by the Department of Energy Office of Energy Efficiency and Renewable Energy Wind Energy Technologies Office. The views expressed herein do not necessarily represent the views of the DOE or the Government. This report is available at no cost from the National Renewable Energy Laboratory ( nrel ) at Department of Energy (DOE) reports produced after 1991 and a growing number of pre-1991 documents are available free via Cover Photos by Dennis Schroeder: (clockwise, left to right) nrel 51934, nrel 45897, nrel 42160, nrel 45891, nrel 48097, nrel 46526.

3 nrel prints on paper that contains recycled content. Acknowledgments This work was authored by Alliance for Sustainable Energy, LLC, the manager and operator of the National Renewable Energy Laboratory for the Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided by Department of Energy Office of Energy Efficiency and Renewable Energy, Wind Energy Technologies Office. The views expressed in the article do not necessarily represent the views of the DOE or the Government. The Government retains and the publisher, by accepting the article for publication, acknowledges that the Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for Government purposes. ivThis report is available at no cost from the National Renewable Energy Laboratory at Nomenclature ABLS olver atmospheric boundary layer solver AWAE ambient wind and array effects (module) a ( r )

4 Axial induction factor, distributed radially aK coherence decrement parameter BEM blade-element momentum bK coherence offset parameter CO HWkDfl, COY HWkDfl, CxHWkDfl, and CxYHWkDfl calibrated parameters in the horizontal wake-deflection correction cmax maximum blade chord length CMeander calibrated parameter for wake meandering CNearWake calibrated parameter in the near-wake correction CWakeDiam calibrated parameter in the wake-diameter calculation CDMax Amb, CDMin Amb, CExp Amb, and CFMin Amb calibrated parameters in the eddy-viscosity filter function for ambient turbulence CDMax Shr , CDMin Shr , CExp Shr, and CFMin Shr calibrated parameters in the eddy-viscosity filter function for the wake shear layer AzimAvgCt( r ) and FiltAzimAvgCt( r ) azimuthally averaged thrust-force coefficient (normal to a rotor disk), distributed radially, and its low-pass time-filtered value Cohi , j magnitude of partial coherence between points i and j DLL dynamic-link library DWM dynamic wake meandering DGrid Assumed rotor diameter when generating TurbSim inflow DRotor and FiltDRotornp rotor diameter and its low-pass time-filtered value at wake plane np DWakenp wake diameter at wake plane np FLORIS FLOw Redirection and Induction in Steady state f frequency fc cutoff (corner) frequency of the low-pass time filter ~fnb( r ) aerodynamic applied loads distributed radially per unit length for blade nb fmax maximum excitation frequency F Amb( x ) eddy-viscosity filter function associated with ambient turbulence F Shr( x )

5 Eddy-viscosity filter function associated with the wake shear layer HFM high-fidelity modeling HPC high-performance computer I three-by-three identify matrix K velocity components u , v , and w k Amb calibrated parameter for the influence of ambient turbulence in the eddy viscosity k Shr calibrated parameter for the influence of the wake shear layer in the eddy viscosity LES large-eddy simulation MFoR moving frame of reference MPI message-passing interface NaN not a number nrel National Renewable Energy Laboratory N and n number of discrete-time steps and discrete-time-step counter Nb and nb number of rotor blades and blade counter NPolarnp and nPolar number of points in the polar grid of wake plane np and point counter NWake and nWake number of wakes overlapping a given wind data point in the wind vThis report is available at no cost from the National Renewable Energy Laboratory at domain and wake counter NP and nP number of wake planes and wake-plane counter Nr and nr number of radial nodes

6 And radii counter Nt and nt number of wind turbines and turbine counter OF OpenFAST (module) OpenMP open multiprocessing ~ pHub global position of a rotor center ~ pPlanenp global position of the center of wake plane np RAM random-access memory RSS root-sum-squared r and rPlane radius in the axisymmetric coordinate system rPlane radial unit vector in the axisymmetric coordinate system S global X -, Y -, and Z -coordinate SC super controller (module) SOWFA Simulator fOr Wind farm Applications t simulation time T IAmb and FiltT IAmbnp ambient turbulence intensity of the wind at a rotor and its low-pass time-filtered value for wake plane np ud discrete-time inputs VAdvect advection speed of the synthetic wind data ~VHigh Amb ambient wind across a high-resolution wind domain around a turbine ~VLow Amb ambient wind across a low-resolution wind domain throughout the wind farm ~VHigh Dist disturbed wind across a high-resolution wind domain around a turbine ~VLow Dist disturbed wind across a low-resolution wind domain throughout the wind farm VHub mean hub-height wind speed ~VPlanenp and Filt~VPlanenp advection, deflection.

7 And meandering velocity and its low-pass time-filtered value of wake plane np Vr radial velocity in the axisymmetric coordinate system VWakernp ( r ) radial wake-velocity deficit at wake plane np, distributed radially VTK Visualization Toolkit DiskAvgVRelx and FiltDiskAvgVRelx rotor-disk-averaged relative wind speed (ambient plus wakes of neighboring turbines plus turbine motion), normal to the disk, and its low-pass time-filtered value Vx axial velocity in the axisymmetric coordinate system VWakexnp ( r ) axial wake-velocity deficit at wake plane np, distributed radially DiskAvgVWindx and FiltDiskAvgVWindxnp rotor-disk-averaged ambient wind speed, normal to the disk, and its low-pass time-filtered value at wake plane np wnWind weighting in the spatial averaging for wind data point nWind WD wake dynamics (module) WISDEM Wind-Plant Integrated System Design & Engineering Model x and xPlanenp downwind distance from a rotor to wake plane np in the axisymmetric coordinate system X , Y , and Z inertial-frame coordinates, with Z directed vertically upward, opposite gravity, X directed horizontally nominally downwind (along the zero-degree wind direction), and Y directed horizontally transversely viThis report is available at no cost from the National Renewable Energy Laboratory at X , Y , and Z unit vectors of the inertial-frame coordinate system, parallel to the X, Y, and X coordinates xd discrete-time states Xd( ) discrete-time state functions xDisk orientation of a rotor centerline xPlanenp orientation of wake plane np yd discrete-time outputs Yd( )

8 Discrete-time output functions zbot bottom vertical location of synthetic turbulence inflow grid low-pass time-filter parameter t discrete time step (increment) YawErr and Filt YawErrnp nacelle-yaw error of a rotor and its low-pass time-filtered value at wake plane np T eddy viscosity air density 2D two dimensional 3D three dimensional viiThis report is available at no cost from the National Renewable Energy Laboratory at Contents 1 Introduction .. 4 Driver .. 4 Super Controller Module .. 6 OpenFAST Module .. 6 Wake Dynamics Module .. 6 Ambient Wind and Array Effects Module .. 9 Parallelization .. 10 Organization of the Guide .. 11 2 Running .. 12 Downloading the Software .. 12 Compiling Software .. 12 Windows Machine Using Visual Studio .. 12 Mac or Linux Machine Using CMake.

9 12 Running Software .. 12 Windows Machine .. 12 Mac or Linux Machine .. 13 3 Input Files .. 14 Units .. 14 Primary Input File .. 14 Simulation Control .. 14 Super Controller .. 15 Ambient Wind: Precursor in Visualization Toolkit Format .. 15 Ambient Wind: InflowWind Module .. 16 Wind Turbines .. 17 Wake Dynamics .. 18 Visualize .. 20 Output .. 21 Ambient Wind Precursor Files in Visualization Toolkit Format .. 23 Ambient Wind with InflowWind Module Input Files .. 23 OpenFAST Input Files .. 24 4 Output Files .. 26 Echo File .. 26 Summary File .. 26 Visualization Output Files .. 26 Time-Series Results File .. 26 OpenFAST Output Files .. 27 5 Modeling Guidance .. 28 Setup Overview .. 28 Inflow Wind Generation .. 30 High-Fidelity Precursor Ambient Inflow .. 31 Complex Terrain.

10 32 1 This report is available at no cost from the National Renewable Energy Laboratory at Synthetic Turbulence Ambient Inflow .. 32 Low- and High-Resolution Domain Discretization .. 34 Low-Resolution Domain .. 34 High-Resolution Domain .. 35 Parameter Selection .. 35 InflowWind Domain Parameters .. 35 Wake Dynamics Parameters .. 37 Super Controller .. 37 Commonly Encountered Errors .. 39 InflowWind Errors .. 39 6 Theory .. 41 Dynamic Wake Meandering Principles and Limitations Addressed .. 41 Theory Basis .. 42 Driver .. 42 Super Controller (SC Module) .. 45 OpenFAST (OF Module) .. 47 Wake Dynamics (WD Module) .. 49 Ambient Wind and Array Effects (AWAE Module) .. 57 7 Future Work .. 62 Bibliography .. 64 A Primary Input File .. 65 B Ambient Wind File .. 68 C List of Output Channels.