Wind Engineering Module 4.2 WT_PERF Analysis Lakshmi Sankar

Recap In Module 1, we reviewed course objectives, history of wind turbines, and some terminology In Module 2, we developed an actuator disk model of the wind turbine. In Module 3, we reviewed airfoil aerodynamics, analysis and design tools. In Module 4.1, we reviewed blade element theory.

Overview In this module, we briefly review WT_PERF –You may use other software for deliverables #2 (validating a wind turbine performance code) and deliverable #3 (design your own wind turbine for the site chosen in deliverable #1) This software is publicly available from Contact Info: –Marshall L. Buhl, Jr. –NWTC/3811 –National Renewable Energy Laboratory –1617 Cole Blvd. –Golden, CO –United States of America Web: Voice: (303)

WT_PERF Source code and Windows executables are available. For this course, we only need the executable. Download WT_PERF, unzip is into folders Print out the user guide. To run the code, in an MS DOS wind type WT_Perf where input file has extension wtp

Sample Input Files WT_PERF comes with several sample input files. Start with one of these, and modify for your own needs. These are in a folder named CertTest –CertTest/Test01_UAE.wtp –CertTest/Test02_AWT27.wtp –CertTest/Test03_CART3.wtp –CertTest/Test04_WP15.wtp –CertTest/Test05_WL8.wtp

Common Extensions All output files use the same root name as the input file. They will have different extensions. The extensions are as follows: –bed – the blade-element data –ech – the echo of the input data –oup – the primary output file Run the code for a supplied input file, and compare your output files against the supplied output files. The data is in ASCII format and may be plotted using Excel, Tecplot, or your favorite plotting tools.

Sample Input file, Header At the top of the input file. Describes the wind turbine you are modeling. Example: WT_Perf Test01 input file. UAE Phase 3 turbine (Non-dimen, English, Space, PROP-PC). Compatible with WT_Perf v3.00f This info is echoed in oup files.

Sample Input File, Input Configuration The next few lines specify whether you want the input to be written out to the.ech output file, whether your input is dimensional, and which system of units you are using. False Echo: Echo input parameters to".ech"? False DimenInp: Turbine parameters are dimensional? False Metric:

Model Configuration If there is a yaw angle, or if the turbine is large, wind velocity and total velocity may vary radially and azimuthally. You also specify how many iterations are needed for computing a, a’ 16 NumSect: Number of circumferential sectors MaxIter: Max number of iterations for induction factor. 1.0e-6 ATol: Error tolerance for induction iteration. 1.0e-6 SWTol: Error tolerance for skewed-wake iteration.

Algorithm Flags We next specify which of the corrections we are using (hub loss, tip loss, etc) True TipLoss: Use the Prandtl tip-loss model? False HubLoss: Use the Prandtl hub-loss model? True Swirl: Include Swirl effects? True SkewWake: Apply skewed-wake correction? True AdvBrake: Use the advanced brake-state model? True IndProp: Use PROP-PC instead of PROPX induction algorithm? False AIDrag: Use the drag term in the axial induction calculation? False TIDrag: Use the drag term in the tangential induction calculation?

Turbine Data We next specify turbine geometry. Only the radius is dimensional (feet since we chose the British system) 3 NumBlade: Number of blades RotorRad: Rotor radius [length]. 0.2 HubRad: Hub radius [length or div by radius]. 3.5 PreCone: Precone angle, positive downwind [deg]. 0.0 Tilt: Shaft tilt [deg] Yaw: Yaw error [deg] HubHt: Hub height [length or div by radius]. 16 NumSeg: # of segments (entire rotor radius). Pre-cone angle is the prebuilt coning angle of the blade relative to the plane of rotation. –Instead of being flat in the plane of rotation, the blade cones upwards or downwards Manufacturers sometimes build this into the rotor to reduce stresses at the root due to bending moments. In the performance code, the coning reduces the rotor disk radius from R to R times cosine of the coning angle, 16.5 cos(3.5 deg) feet in the above example.

Precone Angle The upward flexing of a rotor blade due to lift forces acting on it is called coning. Coning is the result of lift and centrifugal force acting on a blade in flight. The lift force is almost 7 percent as great as the centrifugal force, which causes the blade to deflect upward about 3° to 4°. The preconed hub lets the blades operate at normal coning angles without bending, which reduces stress.

Accounting for pre-Cone Plane of Rotation Coning Angle Radius is R times cos(coning angle) R

Turbine Data (Continued) We next specify the rotor blade at a number of radial locations. RElm Twist Chord AFfile PrntElem False False False False False False False False False False False False False False False False Radial location, twist on degrees, chord non-dimensionalized By tip radius, airfoil family, and whether we want details About the element printed or not.

Aerodynamic Data We next supply density, kinematic viscosity, and the coefficient which determines if wind speed varies with height across the rotor diameter. We also give the name of the airfoil file(s) Rho: Air density [mass/volume] KinVisc: Kinematic air viscosity ShearExp: Wind shear exponent(1/7 law) False UseCm: Cm data included in the airfoil tables? 1 NumAF: Number of airfoil files. "airfoils/unsteadyaeroexp/s809_cln.dat" AF_File: List of NumAF airfoil files.

Other input We finally specify how we want our output, the range of wind speeds, and range of RPM values, and range of pitch angles to examine. Some of the input flags are not shown here.. 3, 4, 1 PitSt, PitEnd, PitDel: First, last, delta blade pitch (deg). 72, 73, 1 OmgSt, OmgEnd, OmgDel: First, last, delta rotor speed (rpm). 15, 75, 1 SpdSt, SpdEnd, SpdDel: First, last, delta speeds.

Output Files The output files contain valuable and useful results. These include power, power coefficient, torque, thrust, thrust coefficient, root bending moment, sectional loads, etc. Sample output files are found at: CertTest/TestFiles/Test01_UAE.bed CertTest/TestFiles/Test01_UAE.oup CertTest/TestFiles/Test02_AWT27.bed CertTest/TestFiles/Test02_AWT27.oup CertTest/TestFiles/Test03_CART3.bed CertTest/TestFiles/Test03_CART3.oup CertTest/TestFiles/Test04_WP15.bed CertTest/TestFiles/Test04_WP15.oup CertTest/TestFiles/Test05_WL8.bed CertTest/TestFiles/Test05_WL8.oup

Source Code The source code of the most recent version is written in Fortran 90. Please look at the following files if you are curious about how these programs are written. Source/SetProg.f90 Source/WT_Perf.f90 Source/WTP_Mods.f90 Source/WTP_Subs.f90