This document summarizes research on a new glass/polyester composite wind turbine blade design with thick airfoils conducted by researchers at the IET-Wind National Energy Wind Turbine Blade R&D Center. A 10.3m prototype blade was manufactured and tested up to 420% of the extreme design loads without failure. Finite element analysis validated the structural behavior and failure predictions of the blade, capturing strains, deflections, and failure modes. The new blade design showed improved buckling resistance and strength over conventional designs. A 100kW wind turbine with the new blades is currently undergoing field testing to evaluate performance under real world conditions.

1. Structural Performance of A Glass/Polyester Composite Wind Turbine Blade with Flatback and Thick Airfoils
Authors: X. Chen*, Z.W. Qin, X.L. Zhao, J.Z. Xu Corresponding author: X. Chen (chenxiao@iet.cn) Presenter: Z.W. Qin (qinzhiwen@iet.cn) IET-Wind National Energy Wind Turbine Blade R&D Center Institute of Engineering Thermophysics (IET) Chinese Academy of Sciences (CAS)

2. IET-Wind at a Glance
- 2 wind tunnels: 0.5x0.5x5 m, 2.5x0.8x6 m 3x4x20 m (under construction)
- PIV experimental system
- Pressure Scanner
- Constant temperature anemometer system
- Computational cluster: 38 cpus, 200 cores
- Commercial and in-house CFD codes
 Aerodynamics & Aero-elastics & Aero-acoustics (3As)
 Structures & Materials
 Manufacturing
 Field Testing and Validation
- MTS bi-axial static/fatigue testing platform (up to100m) (under construction)
- Bending-Torsion component testing rig
- Material and components fatigue testing machine
- Lightning test equipment
- FORCE AMS-64 blade defect scanner
- 100kW WT blade testing platform
- 3As/structure/power output testing
- New design concept validation
- Blades up to 70 m
IET-Wind Members: Director: Prof. J.Z. Xu Profs.: 7 Asso. Profs.: 8 Ass. Profs.: 14 Other staffs and engineers: 13 Phd and Msc Students: 30+

3. Wind Energy Development in China
China’s 2020 target: In total: 200 GW, Offshore: 30 GW
Remaining Challenges:
Failure/buckling of transition region
Failure/buckling of trailing edge
Delamination of spar caps
Overall stiffness of the blades

4. Flatback airfoil
Sharp TE airfoil
Thick airfoil
Thin airfoil
Thin airfoil
Spar cap with transversely uniform thickness
Spar cap with transversely stepped thickness
Fig. 1 Structural features of blades proposed by CAS
IET-Wind New Concepts of Blade Design
Expected advantages
• Improved local buckling resistance
• Large stiffness and strength in the mid-span region
• Strong root transition region
• Improved aerodynamic performance
• Reduced manufacture cost

5. Manufacturing of 10.3 m Prototype Blade

6. Certification and Failure Test
Edgewise bending: 0%40%60%80%100% Pdextreme
Flapwise bending: 0%40%60%80%100%Pdextreme Blade failure
8m
4m
8m
4m

7. 0.00
0.02
0.04
0.06
0.08
0.10
0.12
0 2 4 6 8 10 12
Deflection (m)
Blade span (m)
Test
Classic Beam Theory
100%
80%
60%
40%
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0 2 4 6 8 10 12
Deflection (m)
Blade span (m)
Test
Classic Beam Theory
210%
180%
140%
100%
80%
60%
40%
Edgewise Flapwise
Blade Deflection

8. Blade Strains
0%
50%
100%
150%
200%
250%
-8000 -6000 -4000 -2000 0 2000 4000 6000 8000
% Test load
Spar cap strains (μ)
SS-2.0m
PS-2.0m
SS-5.5m
PS-5.5m
Failure load=220%
0%
50%
100%
150%
200%
250%
-1500 -1000 -500 0 500 1000
% Test load
Aft panel strains (μ)
Failure load=220%
Fig. 8 Strains on aft panels at 2 m
0%
50%
100%
150%
200%
250%
-200 -150 -100 -50 0 50 100 150 200
% Test load
Shear web strains (μ)
Failure load=220%
0%
50%
100%
150%
200%
250%
-600 -450 -300 -150 0 150 300
% Test load
Flatback strains (μ)
Failure load=220%

9. Blade Failure Characteristics
8m
4m
Blade failure at the mid-span of the blade at 220%Pdextreme with UD laminate crushing in the spar cap.

10. Second Failure Test
4m
Purposes:
• Fail the inboard region of the blade
• Examine the failure mode
Method:
• Continuously loading using 4-m crane
Results:
• No failure detected up to 420% Pdextreme
• Loading aborted due to safety concern

11. Finite Element Analysis
Purposes:
• Complement experiment to further understand structural behavior of the blade
• Providing an effective numerical model for the future parametric study.
Model Information:
• Nonlinear analysis with 24,700 shell element “s4r” in Abaqus/standard
• Fixed root boundary and distributed point loads simulating test loads
• 2D Tsai-Wu Criteria used for predicting composite failure

12. 0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 2 4 6 8 10 12
Deflection (m)
Blade span (m)
Test
FEA
210%
180%
140%
80%
60%
40%
100%
0.00
0.05
0.10
0.15
3.9 4 4.1
-2,000
0
2,000
4,000
6,000
8,000
0 1 2 3 4 5 6 7 8 9 10
Strain ε11 (μ)
Flap_Max
系列1
Test, 220%
系列3
FEA,220%
Test, 100%
Test, 210%
-4,000
-2,000
0
2,000
4,000
6,000
8,000
0 1 2 3 4 5 6 7 8 9 10
Strain ε11 (μ)
Flap_Max
系列1
Test, 220%
系列3
FEA,220%
FEA, 100%
FEA, 210%
-8,000
-6,000
-4,000
-2,000
0
2,000
4,000
6,000
8,000
0 1 2 3 4 5 6 7 8 9 10
Strain ε11 (μ)
Blade span (m)
Pressure side
Suction side
Finite Element Model Validation
Blade deflection Spar cap strain

13. Prediction on the 1st Failure Test
5.2 0 m
Spar ca p
6.3 0 m
Fig. 15 Predic ted failure at 22 0% test lo ads
4m
8m
At 220%Pdextreme
At 220%Pdextreme
4m
8m
FE Model:
Failure mode
Failure location

14. Prediction on the 2nd Failure Test
Sp ar cap
Fig. 16 Spar cap failure of inboard region at 543% test lo ad
4m
Fig. 17 First buckling mode of inboard Buckling frequency i s 4.45
4m
Linear buckling region @ 445% Pdextreme
Composite failure region @ 543% Pdextreme
Failure load:
FEA: 543%, 445%
Test: at least 420%

15. New conceptual design of wind turbine blades were proposed by IET-Wind. Experimental study and FE analysis were carried out on a 10.3 m prototype blade to verify the proposed design. It was found that：
The proposed blade exhibited good buckling resistance at trailing edge and the maximum chord panel which are usually susceptible to local instability for the blades with conventional designs.
Root transition region exhibited high ultimate strength and survived over 4 times of extreme design loads. Further weight reduce is possible by material tailoring.
The blade showed a preferred failure mode of composite crushing by which the material strength was fully utilized.
FE modeling method was proved to be efficient to capture spar cap strains, deflection and the failure of the blade. It can be used to model large blades with new design concepts proposed by IET-Wind.
Conclusion

16. The proposed blades have been installed on a 100kW wind turbine and the field test is currently in process in order to study aerodynamics, aeroelastics, aeroacoustics and structures of the blades in the real world. Thank you for your attention.
Future Work