WINDTURBINE WITH SLENDER BLADE

• US 20090068018A1
• Filed: 10/02/2008
• Published: 03/12/2009
• Est. Priority Date: 04/02/2006
• Status: Active Grant

• Current Assignee: Wobben Properties Gmbh (Aloys Wobben Stiftung)
• Original Assignee: Cortenergy BV
• Inventors: CORTEN, Gustave Paul
• Granted Patent: US 8,182,231 B2
• Time in Patent Office: Days
• US Class Current: 416/223.R
• CPC Class Codes: F03D 1/0633 of the blades
• CPC Class Codes: F03D 1/0641 of the section profile of the blades, i.e. aerofoil profile
• CPC Class Codes: F03D 7/0256 Stall control adjusting the blades in stall position F03D7/0224
• CPC Class Codes: F05B 2240/122 Vortex generators, turbulators, or the like, for mixing by creating turbulence F05B2260/222
• CPC Class Codes: F05B 2240/3062 Vortex generators
• CPC Class Codes: Y02E 10/72 Wind turbines with rotation axis in wind direction

Abstract

Wind turbine with a rotor blade relatively insensitive to turbulence because it is more slender than prior blades and is nevertheless able to generate sufficient lift by virtue of the fact that flow enhancing elements such as vortex generators combat flow separation. The slenderness is defined by the chord numbers C and D of which C is defined as C=Nc_rc_lrλ²/R², in which N is the number of blades, c_r is the local chord, c_l the lift coefficient, r the radial position, λ the tip speed ratio and R the rotor radius. Subsequently, the chord should be less than what follows from the equation C=M in which M=−1.19+9.74C_p−21.01C_p²+17.50C_p³ and C_p is the power coefficient. This wind turbine is subject to about 2-12% less operational loads and to about 5-40% reduced survival wind speed loads compared to classical designs.

Claims

1. Wind turbine comprising a blade with an aerodynamic profile said profile having in the range of 0.2R to 0.95R and in particular of 0.5R to 0.95R a 10 minutes averaged lift coefficient c_l larger than 1.1, particularly larger than 1.2 and more particularly larger than 1.4 and more particularly preferably about 1.6.

2. Wind turbine according to claim 1 wherein said profile within the range of 0.5R to 0.95R is operated at a 10 minute averaged angle of attack which differs of the 0-lift angle of said profile by more than 10°

, particularly more than 12° and

more particularly more than 14° and

more particularly preferably by about 16°

.

3. Wind turbine according to claim 1, wherein for tip speed ratios λ

pertaining to the undisturbed wind speeds between 8 and 10 m/s, the chord number D (=Nc_rr λ

²/R²) for said blade between 0.5R and 0.8R and or the chord number D averaged over the range between 0.5R and 0.8R is less than 3.00, and particularly less than 2.75, and more particularly less than 2.50.

4. Wind turbine according to claim 1 of less than 5 m diameter, wherein for tip speed ratios λ

pertaining to the undisturbed wind speeds between 8 and 10 m/s, the chord number D (=Nc_rrλ

²/R²) of said blade between 0.5R and 0.8R is less than 4.50, and particularly less than 4.00, and more particularly less than 3.50.

5. Wind turbine according to claim 1 wherein in the case that the power coefficient ⅓

<

C_p<

16/27 that M=−

1.19+9.74C_p−

21.01C_p²+17.50C_p³ and that in said case in the radial range between 0.5R and 0.9R for a horizontal axis turbine and between 0.8R and R for a vertical axis turbine, the local chord is smaller than which follows from the equation C=M and or the average chord in said ranges is smaller than which follows from the equation C=M assuming that c_l=1.1 and particularly that c_l=1.3 and more particularly that c_l=1.5 and more particularly that it preferably is about 1.7.

6. Wind turbine according to claim 1 wherein within the range from 0.4R to 0.95R, and particularly from 0.5R to 0.8R a lift increasing means is integrated with said blade or is attached to it as a separate element and in particular that said lift increasing means considers vortex generators.

7. Wind turbine according to claim 1 comprising first type fibres which are located between 5% c and 70% c on both the aerodynamic pressure side and the aerodynamic suction side, wherein the cross section of said fibres at the suction side (46) compared to the cross section of said fibres at the pressure side (48) in the radial range between 0.3R and 0.7R is at least 20% larger and particularly 30% larger and more particularly 40% larger.

8. Wind turbine according to claim 1 comprising first type fibres which are located between 5% c and 70% c wherein within a cross section in the radial range between 0.3R and 0.7R said unidirectional fibres at the aerodynamic pressure side consist of at least 25% carbon fibres and particularly that said unidirectional fibres at the aerodynamic suction side comprise for at least 25% glass fibres.

9. Wind turbine according to claim 1 with at the suction side an inlet (85) located at a radial position between 5% R and 70% R wherein said inlet (85) is via a channel (87) connected to an outlet (86) located at a radial position which is relative to the inlet larger by at least a factor 0.9√

2, particularly a factor √

2 and more particularly a factor √

3.

10. Wind turbine according claim 1 wherein having a rotor the diameter of the rotor is larger than 60 m, particularly larger than 80 m and more particularly larger than 100 m.

11. Wind turbine according to claim 1 of the horizontal axis type wherein said blade in the direction from the tip (19) towards the root (17) at a radial position between 0.7R and 0.2R splits at division (75) in an upper blade (76) and a lower blade (77) with in between a free space (79) and that both the upper blade and the lower blade contribute to the aerodynamic lift and in particular that at a certain radial position the distance (74) between the lower and the upper blade is larger than 5% R and more in particular is larger than 10% R.

12. Wind turbine according to claim 1 wherein said blade comprises profiles of at least 25% thickness which are used at radial positions larger than 0.55R, and particularly larger than 0.65R and more particularly larger than 0.75R.

13. Wind turbine according to claim 1 wherein said blade comprises vortex generators (41) located at the pressure side of a profile which preferably is thicker than 25% c and particularly thicker than 30% c and more particularly thicker than 35% c, wherein said vortex generators (41) are located at a chord position larger than 30% c, particularly larger than 50% c and more particularly larger than 70% c.

14. Wind turbine according to claim 1 wherein said blade comprises an airfoil with camber of more than 6% c particularly more than 8% c and more particularly more than 10% c.

15. Wind turbine according to claim 1 wherein said blade comprises an airfoil with vortex generators (65) which have a length of more than 10% c and more particularly more than 20% c and even more particularly more than 30% c.

16. Wind turbine according to claim 1 of the vertical axis type wherein the tip speed ratio λ

is smaller than 3½ and

particularly smaller than 3 and more particularly smaller than 2½

.

17. Wind turbine according to claim 1 having vortex generators wherein said vortex generators comprise a surface of one of the plastics PVDF, FEP, PEEK, PI, PEI, PES and PFTE and particularly that said vortex generators entirely consist of said plastics.

18. Wind turbine according to claim 1, having vortex generators wherein said vortex generators are arranged at an angle of less than 10°

, and particularly less than 5°

, to the tangentials related to the centre of rotation.

19. Wind turbine according to claim 1 wherein the upstream side of more than 70% of said vortex generators has a shorter distance to the centre of rotation than the downstream side.

20. Wind turbine according to claim 1, wherein upstream of a base line with vortex generators, extra vortex generators are installed at a greater distance apart.

21. Wind turbine according to claim 1 having vortex generators wherein said vortex generators are arranged one behind the other in the direction of flow generate vortices of the same rotational direction.

22. Wind turbine according to claim 1 having vortex generators wherein the effectiveness of the vortex generators is regulated by changing the position, or opening them out to a greater or lesser degree, or submerging them partly in the blade surface and in particular by activating the vortex generators by MEM tabs or piezoelectrics.

23. Wind turbine according to claim 1 comprising airfoil sections wherein the ratio c_l,max/c_l,min is less than −

1.2−

0.2·

% cam and in particular less than −

1.4−

0.2·

% cam.

24. Wind turbine according to claim 1 wherein said turbine has two active control options and in particular has one active control option and more in particular has no active control options, said control options are in the group pitch control and variable rotation speed control.

25. Method wherein a first blade of an existing turbine is removed and is replaced by an other blade wherein said existing turbine with said other blade is according to claim 1 and particularly that said other blade in the range of 0.7R to 0.95R comprises a local chord c_r which is at least 10% and more particularly at least 20% smaller than the local chord c_r of said first blade.