NREL{I'P-257-4674 • UC Category: 261 • DE92010579 User's Guide e NREL Force and Loads Program (FLAP) Version 2.2 Alan D. Wright Q�IE.. !.. • National Renewable Energy Laboratory (formerly the Solar Energy Research Institute) 1617 Cole Boulevard Golden, Colorado 80401-3393 A Division of Midwest Research Institute Operated for the U.S. Department of Energy under Contract No. DE-AC02-83CH10093 August 1992 NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, com­ pleteness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily con­ stitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. Printed in the United States of America Available from: National Technical Information Service U.S. Department of Commerce 5285 Port Royal Road Springfield, VA 22161 Price: Microfiche A01 Printed Copy A11 Codes are used for pricing all publications. The code is determined by the number of pages in the publication. Information pertaining to t_he pricing codes can be found in the current issue of the following publications which are generally available in most libraries: Energy Research Abstracts (ERA); Govern­ ment ReportsAnnouncements and Index ( GRA and I); Scientific and TechnicalAbstract Reports (STAR); and publication NTIS-PR-360 available from NTIS at the above address. Summary The following report gives the reader an overview of and instructions on the proper use of the National Renewable Energy Laboratory ,Eorce and Loads Analysis �ogram (FLAP, version 2.2). It is intended as a tool for prediction of rotor and blade loads and response for two- or three-bladed rigid hub wind · turbines. The effects of turbulence are accounted fo r. The objectives of thereport are to give an overview of thecode and also show the methodsof datainput and correct code execution steps in order to model an example two-bladed rigid hub turbine. A large por­ tion of the discussion (Sections 6.0, 7.0, and 8.0) is devoted to the subject of inputting and running the code for wind turbulence effects. The ability to include turbulent wind effects is perhaps the biggest change in the code since the release of FLAP version 2.01 in 1988. This report is intended to be a user's guide. It does not contain a theoretical discussion on equations of motion, assumptions, underlying theory, etc. It is intended to be used in conjunction with Wright, Buhl, and Thresher (1988) . � i Hopefully, this report will assist new users in the understanding of code input preparation and correct code execution. "I •f .. I'\' I I .) ···� r iii Table of Contents Summary . ................, . iii Nomenclature . vii 1.0 Introduction . .. .. .. .. .. .. .. .. .. .. .. 1 2.0 Code Overview . 2 i l 3.0 New Code Inputs ......................................·. .. 4 ' i \ ' 4. 0 Example Turbine Description . .. .. .. .. .. .. .. 5 r l 'l ' ' I 5.0 Preparation of Input Data . .. .. .. .. .. .. .. .. .. .. .. 9 6.0 Preparation of Turbulent Wind Input Data. .. .. .. .. .. .. .. .. 14 7.0 Input of Turbu�ence Data to FLAP. : .. .. .. .. .. .. .. .. 15 8.0 Example Interactive Run . .............. ..,) . .. .. .. .. 17 8.1 Module 1-FI...AP1 . .. .. .. .. .. .. .. .. .. .. 17 8.2 Module 2-FI...AP2 . .. .. .. .. .. .. .. 17 1 L' 9.0 Conclusions . .. .. .. .. .. .. .. .. .. .. .. .. .. 19 10.0 References. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 20 11.0 Acknowledgments . .. .. .. .. .. .. .. .. .. .. 21 Appendix A: Module 1 Input File, Interactive Run Listing, and Output Files ..... ....... A-1 Appendix B: Module 2 Interactive Run Listing and Output Files . ....... .. ..... .... B-1 Appendix C: Module 1 Listing ................................. ........... C-1 Appendix D: Module 2 Listing ............................................ D-1 Appendix E: . Modules 1 and 2 Flowcharts. E-1 iv c \ ' \ I � List of Figures 4-1 illustration of example turbine . .. .. .. .. .. .. .. .. .. .. .. 5 r 4- 2 Turbine blade planform, thickness,and twist . .. .. .. .. .. 6 4- 3 Turbine blade stiffness distribution . 6 -1.- I 4- 4 Turbine blade weight distribution . 7 . 4- 5 Liftprofile for the LS(1) airfoil . 7 · l 5-1 illustration of rotor geometry......................................... 10 ·- jI I y i i; - I ! __( � ·-- I 1 - j I. __ _ I v • 1 ; l List of Tables 4- 1 Example Turbine Specifications . , . 8 • 1 i ' �· ' ' 1 • I r-- � : J t_j vi Nomenclature CD Drag coefficient CL Liftcoefficient l deg Degrees I· 1 ft Feet m Meters rad Radians .Q Rotor rotation rate (RPM) t \ \I vii 1.0 Introduction The following report is intended to be a guide for the correct use of the National Renewable Energy Laboratory (NREL) Force and Loads Analysis f_rogram (FLAP, Version 2.2). The original equations of motion that formed the basis for FLAP (version 2.01) have been retained. The main change is the ability to calculate blade response and loads caused by turbulence. Degrees of freedom include four-blade elastic flap modes. A prescribed time-dependent sinusoidal yaw function can be input to the code. The report gives a general overview of the code. A description of new input variables (compared to FLAP version 2.01 of 19 88) is given. Then, an example of a two-bladed, rigid hub wind turbine is described. Preparation of the basic data input file for. this two-bladed turbine is described. Then, the methods of turbulent wind input preparation and input of turbulence to FLAP are explained. Finally, an interactive run session for both modules is illustrated. Code listings and output results are contained in the appendices. 1 2.0 Code Overview FLAP (Eorce and LoadsAnalysis £rogram)analyzes two- or three-bladed rigid hub rotors. Itpredicts blade loads that result from such effects as gravity, windshear, to wer shado w, and turbulent wind fluctuations. Italso predicts shaftloads caused by gravity, windshear, and to wer shado w. Degrees of freedom included in this model are four elastic flap modes for the blade. Blade torsion and edge wise degrees of freedomare not included. The to wer top is assumed to be fixedin space. The model assumes constant rotor speed. Al though machine ya w is not considered to be a degree of freedom,a prescribed time-dependent ya w motion can be input to the code. FLAP is basically a derivative of the force and Loads Analysis £rogram (FLAP;Version 2.01) (Wright, Buhl,and Thresher,19 8 8). This version of FLAP is similar to FLAP 2.01 in that a quasi-steady linear aerodynamic model is used to compute blade aerodynamic forces. The liftis modeled as a linear function of angle of attackup to stall. Past stall, liftis set equal to a constant. The drag is modeled as a quadratic function involving lift coefficient. For more details, see Section 5.0 of Wright, Buhl,and Thresher (19 88). FLAP is composed of two modules (FLAP1 and FLAP 2). The first module is a preprocessor that reads blade and machine property data Itcomputes such items as blade flap wise frequencies andmodeshapes as well as stiffness,mass, coriolis, and other matrices . These quantities are variables thatdo not generally change from one run to the next and, thus,are computed once. Distributed blade properties such as the blade's stiffness, weight, twist,and chord may be read into Module 1 at unevenly spaced points. The input data is then interpolated to form sets of evenly spaced data. Ano ther capability of this module is calculation of the blade's flap wise frequenciesand modeshapes. This information is written to a file for examination by the user. From this information, the user can check the effects of mass and stiffness on blade frequencies and modeshapes. We assume in this version of FLAP that bo th blades have identical mass, stiffness,tw ist, and chord )' distributions. In Module 1, mass, stiffness,and other matrices are calculated for only one blade. The effects of mass,pitch, and twist imbalances are not accounted for in this model. ,[ .. ) The second module (FLAP 2)calculates the blade equations of motion and computes blade and lo w-speed shaftloads. The code calculates the rotor response to such input as gravity, windshear,to wer shado w, ya w misalignment,and ya w rate. The response to these inputs is generally a steady-state one. Thecode i is run wi th initial valuesfor theblade deflection and velocity. Once the blade reaches a steady-state trim . J solution,the blade deflection and loads are calculated and written to a file. The shaftloads are also calculated and written to a separate file. The rotor response and load calculations resulting from time-dependent ya w motion or turbulent wind input is handled differently than the trim case. In those cases, a steady-state trim solution is calculated first,before the code enters the transient portion of the solution process. The results of this trim solution are then used as initialconditions for the transient analysis. After this trim solution is completed,the time clockis started,and the model is run, wi th the ya w function evaluatedat each azimu th position. The ya w­ function values for the initial ya w-angledisplacement, ya w-angle amplitude,and maximum ya w velocity . j are set by the user during the model-run setup. Because the ya w function is given independently of the rotor model, the model solution from one rotor revolution to the next will not be steady state. l I 2 The number of revolutions to be run in the yaw solution is set by the user during run setup.