DESCRIPTION FOR THE PART 1 OF THE PROJECT
DOCUMENT # 1
(due April 30th Monday)
1- INFORMATION ON THE BLADE PROFILE, AERODYNAMIC
COEFFICIENTS AND LOAD CASES
The blade that is going to be designed has a linear taper and nonlinear twist, and uses the S809 airfoil. In the calculation of the external aerodynamic loading, convention shown in Fig. 1 can be used as a guide.
Figure 1. Aerodynamic force coefficient conventions [1]
Basic parameters of the wind turbine
- Blade cross section and planform: NREL S809, tapered and twisted
- Root extension from center of rotation to airfoil transition: 0.883 m (see Fig. 2)
- Each blade attaches to the hub at a point 0.508 m from the center of rotation. There is a cylindrical section at the root that extends from 0.508 m to 0.883 m. The airfoil transition begins at approximately the 0.883 m radial station.
There is a transition from the cylindrical section to the S809 airfoil along the 0.883 m
to 1.257 m region. The transition ends with a 0.737 m chord S809 airfoil at the 1.257
m span station.
- Blade tip pitch angle : 0 degrees
- Blade chord, twist and thickness distribution: see Table 1.
- Twist convention is positive towards feather (See Fig. 3 for feather direction). Values listed are relative to zero twist at the 3.772-m station [75% span on a 5.03-m blade]. Twist is 2.0 degrees toward stall at the tip (See Fig.3)
- Number of blades: 3
- 10.058 m rotor diameter with standard tip or smoke tip
- Hub height: 12.192 m
- Rotational speed: 72 RPM synchronous speed
- Cut-in wind speed: 6 m/s
- Power regulation: stall
- Rated power: 19.8 kW
- Rotational direction: counterclockwise (viewed from upwind – see Fig.4)
Table 1. Blade chord and twist distributions [1,2]
Radial distance (m) / Chord length (m) / Twist (degrees) / Thickness (m)0.0 / Hub-center of rotation / Hub-center of rotation / Hub-center of rotation
0.508 / 0.218 (root hub adapter) / 0.0 (root hub adapter) / 0.218
0.660 / 0.218 / 0.0 / 0.218
0.883 / 0.183 / 0.0 / 0.183
1.008 / 0.349 / 6.7 / 0.163
1.067 / 0.441 / 9.9 / 0.154
1.133 / 0.544 / 13.4 / 0.154
1.257 / 0.737 / 20.05 / 0.154
1.522 / 0.710 / 14.04 / 20.95% chord
1.798 / 0.682 / 9.67 / 20.95% chord
2.075 / 0.654 / 6.75 / 20.95% chord
2.352 / 0.626 / 4.84 / 20.95% chord
2.628 / 0.598 / 3.48 / 20.95% chord
2.905 / 0.570 / 2.40 / 20.95% chord
3.181 / 0.542 / 1.51 / 20.95% chord
3.458 / 0.514 / 0.76 / 20.95% chord
3.735 / 0.486 / 0.09 / 20.95% chord
3.772 / 0.483 / 0.00 / 20.95% chord
4.011 / 0.459 / -0.55 / 20.95% chord
4.288 / 0.431 / -1.11 / 20.95% chord
4.565 / 0.403 / -1.55 / 20.95% chord
4.841 / 0.375 / -1.84 / 20.95% chord
5.030 / 0.356 / -2.00 / 20.95% chord
Sections with S809 airfoil
Figure 2. Blade root and transition region [1]
Figure 3. Tip and root twists of the blade [1]
Figure 4. Definition of upwind and downwind
Aerodynamic coefficients
For aerodynamic coefficients refer to the following references.
[1] : pages 68-74 . Here in Ref. 1 OSU stand for Ohio State University, CSU stands for Colorado State University and DUT stands for Delf University of Technology.
[3] : pages 66-73 . In this document, tables of aerodynamic coefficients refer to Ref.1 mostly.
[4]: Chapter 7 of the report gives the wind tunnel testing and the results, and Appendix F gives the integrated coefficients from all tests
[5]: Qblade is a boundary element momentum method based blade simulation tool. It runs XFLR5 inside and gives the aerodynamic coefficients as a by-product during a blade aerodynamic design. You can download the program from internet. Section 5 of the guide gives explanations on how to design and simulate a rotor or turbine with Qblade. However, in your design project you will not carry out aerodynamic design. All we need is the aerodynamic coefficients so that external aerodynamic loads can be calculated. Rotor and Turbine Design module of Qblade performs 360 polar extrapolation. You are expected to use Qblade to determine aerodynamic coefficients in the range 0-90 degrees. In case wind tunnel data is not sufficient, you may want to fill the missing data from the output of Qblade analysis. Remember in Qblade all you have to do is to carry out an XFLR5 (or XFOIL) analysis and get aerodynamic coefficients until post stall regime. Then, extrapolation routine of Qblade extends the range of aerodynamic coefficients to higher angle of attack.
References 1,3,4 and 5 should be sufficient for the calculation of aerodynamic coefficients. However, you may find other references and use them as well. Actually, in the first part of the project, if you can get more data on the aerodynamic coefficients of S809 airfoil, you can share them with the rest of the class. So, besides the references given above you are also expected to make a literature search in the internet.
Load cases
In the design project, consider the power production design condition of IEC 61400-1 only. Determine the external and internal loads based on:
i) Operation at rated wind speed of 15 m/s
ii) Operation at cut-out wind speed of 20 m/s
Design load cases associated with the power production design condition are given in Table 2 of IEC 61400-1 (look at the modification given at the beginning of the standard. There is an updated version of Table 2) We will use normal turbulence model (NTM) but only consider the steady loading. In addition, since the blade hub height and the blade radius is small, the change of the wind speed along the height can be ignored.
2- FORMAT OF THE PROJECT REPORT
DATE SUBMITTED:
TITLE OF THE DOCUMENT: Give an appropriate title
GROUP MEMBERS:
1- INTRODUCTION
Briefly introduce the project. Describe the tasks accomplished in the first document such as how you performed the external and internal load calculation. Summarize the output you produced.
2- CAD DRAWING OF THE BLADE
Model the blade in a CAD program such as CATIA, Unigraphics etc. Prepare sectional views of the blade sections taken along the various spanwise locations, showing the twist distribution.
3- PRESENTATION ON STRUCTURAL DESIGN SECTION OF IEC 61400-1 DESIGN REQUIREMENTS STANDARD
Read Chapter 7 (Structural Design) of IEC 61400-1 Design Requirements that is linked in the web site. You are expected to prepare a presentation of Chapter 7, emphasizing on the design load cases, load calculation and ultimate limit state analysis.
In the second part of the project, you have to refer to IEC 61400-1 for the calculation of the factors of safety to be used for loads and material properties. Therefore, you are expected to read and understand the contents of chapter 7 of of IEC 61400-1. In the design load cases section, reference is also made to chapter 6 of the standard which gives the wind conditions used with the design load cases. You are expected to familizarize yourself with chapter 6 on external conditions section of IEC 61400-1. Section 3 of the standard gives terms and definitions which will help you in understanding the nomenclature.
4- CALCULATION OF EXTERNAL AERODYNAMIC LOAD
Determine the external aerodynamic loading for the rated wind speed of 15 m/s, and at cut-out wind speed of 20 m/s. Refer to the load cases subsection above.
i) Determine the lift, drag and pitching moment per unit span length of the blade. Refer to the information provided under the “Aerodynamic coefficient” and “Load cases” heading above for the calculation of the external aerodynamic loading. Figure 5 shows the aerodynamic forces decomposed about the aerodynamic center of a typical blade section. Draw the lift per unit span, drag force per unit span and pitching moment per unit span curves. Make sure that you use proper units. Prepare a table showing the external loads (lift, drag and pitching moment ) per unit span of the blade section by section.
Figure 5. External aerodynamic loading decomposed about the aerodynamic center
ii) In this part, determine the running loads in the z and x directions, and pitching moment per span of blade with respect to the x-y-z axis passing through the pitch and twist axis at 30% chord of the root section of the blade. Figure 6 shows the x-y-z axis system on the root section of the blade. Draw the running load per unit span Fz, running load per unit span Fx and pitching moment per unit span curves, similar to the ones in part i. Make sure that you use proper units. Prepare a table showing the external loads (Fx, Fz and My) per unit span of the blade section by section.
Figure 6. External aerodynamic loading decomposed with respect to x-y-z axis passing through 30% chord
5- CALCULATION OF INTERNAL LOADS
* Obtain the internal loads corresponding to the wind speeds of 15 m/s and 20 m/s. Specifically, determine spanwise distribution of shear forces (Vz and Vx (in N !), pitching moment (My (in Nm !)) and bending moments (Mx and Mz (in Nm !)) in a fashion similar to the example we did from Bruhn.
For the number of stations you can use the spanwise stations you used in the external load calculation. Make tables of the internal loads. You should obtain internal loads with respect to the pitch and twist axis at 30% chord.
* Draw spanwise variation of the sectional shear forces (Vx and Vz), pitching moment (My) and bending moment (Mx, Mz) curves. Comment on your results. Keep in mind that the sectional forces that you determine in the first part of the project will be used in the second part to size the blade.
6- DISCUSSION AND CONCLUSION
Make any critical comments you have, discuss your results and conclude by summarizing the tasks accomplished.
References
[1] Hand, M.M.; Simms, D.A.; Fingersh, L.J.; Jager, D.W.; Cotrell, J.R.; Schreck, S.J.; Larwood, S.M. Unsteady Aerodynamics Experiment Phase VI: Wind Tunnel Test Configurations and Available Data Campaigns, NREL/TP-500-29955; Golden, CO: National Renewable Energy Laboratory, 2001.
[2] P. Giguère and M.S. Selig, Subcontractor report - Design of a Tapered and Twisted Blade for the NREL Combined Experiment Rotor, NREL/SR-500-26173, April 1999.
[3] J.M. Jonkman, Modeling of the UAE Wind Turbine for Refinement of FAST_AD, NREL/TP-500-34755, Golden, CO: National Renewable Energy Laboratory, December 2003.
[4] C.P. Butterfield, W.P. Musial, D.A. Simms, Combined Experiment Phase I Final Report, NREL/TP-257-4655, Golden, CO: National Renewable Energy Laboratory, October 1992.
[5] Qblade V0.01, David Marten, , July 2010.