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)

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+

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

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

Manufacturing of 10.3 m Prototype Blade

Certification and Failure Test

Edgewise bending:

0%40%60%80%100% Pdextreme

Flapwise bending:

0%40%60%80%100%PdextremeBlade failure

8m 4m

8m 4m

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 2 4 6 8 10 12

Defl

ecti

on (

m)

Blade span (m)

Test

Classic Beam Theory100%

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

Defl

ecti

on (

m)

Blade span (m)

Test

Classic Beam Theory

210%

180%

140%

100%

80%

60%

40%

Edgewise Flapwise

Blade Deflection

Blade Strains

0%

50%

100%

150%

200%

250%

-8000 -6000 -4000 -2000 0 2000 4000 6000 8000

% T

est

lo

ad

Spar cap strains (μ)

SS-2.0mPS-2.0mSS-5.5mPS-5.5m

Failure load=220%

0%

50%

100%

150%

200%

250%

-1500 -1000 -500 0 500 1000

% T

est

lo

ad

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

% T

est

lo

ad

Shear web strains (μ)

Failure load=220%

Fig. 9 Strains on shear web at 2 m

0%

50%

100%

150%

200%

250%

-600 -450 -300 -150 0 150 300

% T

est

lo

ad

Flatback strains (μ)

Failure load=220%

Fig. 10 Strains on flatback at 2 m

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.

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

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

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 2 4 6 8 10 12

Defl

ecti

on (

m)

Blade span (m)

Test

FEA210%

180%

140%

80%

60%

40%

100%

0.00

0.05

0.10

0.15

3.9 4 4.1

-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

Str

ain

ε1

1(μ

)

Blade span (m)

Flap_Max

系列1

Test, 220%

系列3

FEA,220%

Test, 100%

Test, 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

Str

ain

ε1

1(μ

)

Blade span (m)

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

Str

ain

ε1

1(μ

)

Blade span (m)

Flap_Max

Test_220%

系列1

FEA_220%

系列3Pressure side

Suction side

Finite Element Model Validation

Blade deflection Spar cap strain

Prediction on the 1st Failure Test

5.20 m

Spar cap

6.30 m

Fig. 15 Predicted failure at 220% test loads

4m

8m

At 220%Pdextreme

At 220%Pdextreme

4m

8m

FE Model:

Failure mode

Failure location

Prediction on the 2nd Failure Test

Spar cap

Fig. 16 Spar cap failure of inboard region at 543% test load

4m

Fig. 17 First buckling mode of inboard region at 445% test load

Buckling frequency is 4.45

4m

Linear buckling region @ 445% Pdextreme

Composite failure region @ 543% Pdextreme Failure load:

FEA: 543%, 445%

Test: at least 420%

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

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