U.S. patent application number 12/008690 was filed with the patent office on 2008-12-25 for wind turbine rotor blade with vortex generators.
Invention is credited to Peder Bay Enevoldsen, Soeren Hjort.
Application Number | 20080317600 12/008690 |
Document ID | / |
Family ID | 38089110 |
Filed Date | 2008-12-25 |
United States Patent
Application |
20080317600 |
Kind Code |
A1 |
Enevoldsen; Peder Bay ; et
al. |
December 25, 2008 |
Wind turbine rotor blade with vortex generators
Abstract
A wind turbine rotor blade with an airfoil having a suction side
and a pressure side is provided. The airfoil comprises an inner
airfoil portion and an outer airfoil portion, where the inner
airfoil portion is comparatively thicker than the outer airfoil
portion and provided with vortex generators. The thickness of the
inner airfoil portion is between 30% and 80% of the inner airfoil
portion's chord length, and the vortex generators are located at
the suction side of the inner airfoil portion between 8% and 12% of
the chord length, as measured from the leading edge of the airfoil
portion.
Inventors: |
Enevoldsen; Peder Bay;
(Vejle, DK) ; Hjort; Soeren; (Brande, DK) |
Correspondence
Address: |
SIEMENS CORPORATION;INTELLECTUAL PROPERTY DEPARTMENT
170 WOOD AVENUE SOUTH
ISELIN
NJ
08830
US
|
Family ID: |
38089110 |
Appl. No.: |
12/008690 |
Filed: |
January 11, 2008 |
Current U.S.
Class: |
416/223R |
Current CPC
Class: |
F05B 2240/30 20130101;
F05B 2240/32 20130101; F05B 2240/301 20130101; F03D 1/0641
20130101; F05B 2240/3062 20200801; Y02E 10/72 20130101 |
Class at
Publication: |
416/223.R |
International
Class: |
F01D 5/14 20060101
F01D005/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 12, 2007 |
EP |
07000617.6 |
Claims
1.-5. (canceled)
6. A wind turbine rotor blade, comprising: an airfoil having a
suction side and a pressure side, the airfoil comprising an inner
airfoil portion and an outer airfoil portion, where the inner
airfoil portion is comparatively thicker than the outer airfoil
portion, the thickness of the inner airfoil portion being between
30% and 80% of a inner airfoil portion's chord length; and vortex
generators at the suction side of the inner airfoil portion between
8% and 12% of the chord length, as measured from the leading edge
of the airfoil portion.
7. The wind turbine rotor blade as claimed in claim 6, wherein the
thickness of the inner airfoil portion is between 40% and 65% of
the chord length.
8. The wind turbine rotor blade as claimed in claim 6, wherein all
vortex generators are located at the same chord length.
9. The wind turbine rotor blade as claimed in claim 7, wherein all
vortex generators are located at the same chord length.
10. The wind turbine rotor blade as claimed in claim 6, wherein
vortex generators are present along the whole span of the inner
airfoil portion.
11. The wind turbine rotor blade as claimed in claim 7, wherein
vortex generators are present along the whole span of the inner
airfoil portion.
12. The wind turbine rotor blade as claimed in claim 8, wherein
vortex generators are present along the whole span of the inner
airfoil portion.
13. The wind turbine rotor blade as claimed in claim 9, wherein
vortex generators are present along the whole span of the inner
airfoil portion.
14. A wind turbine, comprising: a rotor blade having an airfoil
having a suction side and a pressure side, the airfoil comprising
an inner airfoil portion and an outer airfoil portion, where the
inner airfoil portion is comparatively thicker than the outer
airfoil portion, the thickness of the inner airfoil portion being
between 30% and 80% of a inner airfoil portion's chord length, and
vortex generators at the suction side of the inner airfoil portion
between 8% and 12% of the chord length, as measured from the
leading edge of the airfoil portion.
15. The wind turbine as claimed in claim 14, wherein the thickness
of the inner airfoil portion is between 40% and 65% of the chord
length.
16. The wind turbine as claimed in claim 15, wherein all vortex
generators are located at the same chord length.
17. The wind turbine as claimed in claim 16, wherein vortex
generators are present along the whole span of the inner airfoil
portion.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of European Patent Office
application No. 07000617.6 EP filed Jan. 12, 2007, which is
incorporated by reference herein in its entirety.
FIELD OF INVENTION
[0002] The present invention relates to a wind turbine rotor blade
with vortex generators and to a wind turbine with at least one of
such rotor blades.
BACKGROUND OF INVENTION
[0003] A state of the art rotor blade for a wind turbine is, e.g.
described in EP 1 314 885 A1. Such a blade comprises a root portion
having a cylindrically shaped cross-section by which the rotor
blade is fixed a hub of the rotor and an airfoil portion with an
aerodynamically shaped cross-section.
[0004] It is usual to subdivide the airfoil portion notionally into
a relatively thick inner airfoil portion and a relatively thin
outer airfoil portion where the inner airfoil portion is located
between the root portion and the outer airfoil portion.
[0005] The wind turbine rotor blade disclosed in EP 1 314 885 A1 is
provided with vortex generators located at the suction side of the
inner airfoil portion.
[0006] Vortex generators which are located on a wind turbine rotor
blade close to the hub portion are also known from WO 02/08600 A1.
In addition, the use of vortex generators is described in WO
00/15961 as well as in EP 0 947 693 A2.
[0007] In Van Rooij, R. P. J. O. M.; Timmer, W. A.: "Roughness
sensitivity considerations for thick rotor blade airfoils", Journal
of Solar Energy Engineering, vol. 125, no. 4, November 2003
(2003-11), pages 468-478, XP00807970 New York, N.Y., US and in
Peter Fuglsang, Christian Bak: "Development of the Riso Wind
Turbine Airfoils" A Sampling of the 2003 EWEC in Madrid, vol. 7,
no. 2, 24 May 2004 (2004-05-24), pages 145-162, XP002436915 John
Wiley & Sons Ltd., different wind turbine rotor blades having a
thickness between 25% and 40.1% as compared to the chord length are
described. The rotor blades are equipped with vortex generators,
which are located at the airfoil's suction side at 20% or 30% of
the chord length, as measured from the leading edge of the
airfoil.
[0008] In the mentioned state of the art, the use of vortex
generators for improving the aerodynamical properties of the wind
turbine rotor blades is described. However, an optimum position of
the vortex generators depends on many parameters. Therefore, a good
position of vortex generators at the outer airfoil portion of a
rotor blade cannot necessarily be expected to be also a good
position of the vortex generators at the inner airfoil portion of
the rotor blade. However, in particular the inner airfoil portion
of the rotor blade has a reduced aerodynamic performance as
compared to the outer airfoil portion. The reason is that the inner
part of the wind turbine rotor blade needs to carry the load from
the entire blade. This means a number of design constrains in order
to achieve sufficient stiffness of the rotor blade. The reduced
aerodynamic performance of the inner airfoil portion compared to
the outer airfoil portion reduces the overall efficiency of a wind
turbine. It is therefore desired to improve the aerodynamic
performance of the inner airfoil portion.
SUMMARY OF INVENTION
[0009] In view of the aforementioned it is an objective of the
present invention to provide an improved wind turbine rotor blade
with vortex generators located such that a sufficient aerodynamic
performance and, at the same time, a high load bearing can be
achieved.
[0010] It is a further objective of the present invention to
provide an improved wind turbine.
[0011] The first objective is solved by a wind turbine rotor blade
according to a independent claim and the second objective is solved
by a wind turbine according to a further independent claim. The
depending claims define further developments of the present
invention.
[0012] An inventive wind turbine rotor blade comprises an airfoil
having a suction side and a pressure side. The airfoil further
comprises an inner airfoil portion and an outer airfoil portion
where the inner airfoil portion is comparatively thicker than the
outer airfoil portion. In addition, the inner airfoil portion is
provided with vortex generators. In the inventive wind turbine
rotor blade the thickness of the inner airfoil portion is between
30% and 80% of the inner airfoil portions chord length. The vortex
generators are located at the suction side of the inner airfoil
portion between 8% and 12% of the chord length, as measured from
the leading edge of the airfoil portion.
[0013] The inventive wind turbine rotor blade provides an improved
stiffness as compared to the state of the art rotor blades with
comparable aerodynamic performance of the inner airfoil portion.
The high stiffness is achieved by the extreme thickness of the
inner airfoil portion which lies between 40% and 80% chord length.
However, usually, thicker blades are related to lower are
aerodynamic performance. In the present invention the lower
aerodynamic performance of an extreme thick airfoil portion is
overcome by positioning vortex generators on the suction side of
the thick inner airfoil portion. Therefore, the combination of the
extreme thickness of the inner airfoil portion and the suitably
located vortex generators allows for wind turbine rotor blades
having a high stiffness in the inner airfoil portion and, at the
same time, a satisfactory aerodynamic performance. Up to now, the
use of vortex generators for extreme thick blades was unknown. Even
in WO 02/08600 A1, where vortex generators are located close to the
root, the airfoil portion carrying the vortex generators is not a
thick airfoil portion.
[0014] A sufficient strength of the wind turbine rotor blades inner
airfoil portion can also be achieved with a thickness between 40%
and 65% chord length.
[0015] To achieve the maximum effect of the vortex generators it is
advantageous when vortex generators are present along the whole
span of the inner airfoil portion. All vortex generators may be
located at the same chord length.
[0016] It should be noted, that the use of vortex generators in the
outer, thinner airfoil portion shall not be excluded by the
invention.
[0017] An inventive wind turbine rotor comprises at least one rotor
blade according to the invention. In particular all rotor blades of
the wind turbine, e.g. all three rotor blades of a three-bladed
wind turbine rotor, are rotor blades according to the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Further features, properties and advantages of the present
invention will become clear from the following description of
embodiments of the invention in conjunction with the accompanying
drawings.
[0019] In the drawings:
[0020] FIG. 1 shows a wind turbine rotor blade in a plane view on
the plane defined by the blade span and the blade chord.
[0021] FIG. 2 shows a chord-wise section through the outer airfoil
portion of the blade shown in FIG. 1.
[0022] FIG. 3 shows a chord-wise section through the inner airfoil
portion of the blade shown in FIG. 1 according to a first
embodiment of the invention.
[0023] FIG. 4 shows a chord-wise section through the inner airfoil
portion of the blade shown in FIG. 1 according to a second
embodiment of the invention.
[0024] FIG. 5 shows a chord-wise section through the airfoil
portion of the blade shown in FIG. 1 according to a third
embodiment of the invention.
[0025] FIG. 6 shows the lift coefficients achieved by the inventive
rotor blades as a function of the wind's angle of attack.
[0026] FIG. 7 shows the drag coefficients of the inventive rotor
blades as a function of the wind's angle of attack.
DETAILED DESCRIPTION OF INVENTION
[0027] FIG. 1 shows a wind turbine blade as it is usually used in a
three-blade rotor. However, the present invention shall not be
limited to blades for three-blade rotors. In fact, it may as well
be implemented in other rotors like one-blade rotors or two-blade
rotors, or even in rotors with more than three blades.
[0028] The rotor blade 1 shown in FIG. 1 comprises a root portion 3
with a cylindrical profile, and a tip 2 which forms the outermost
part of the blade. The cylindrical profile of the root portion 3
serves to fix the blade 1 to a bearing of a rotor hub. The rotor
blade 1 further comprises a so-called shoulder 4 which is defined
as being the location of the blades maximum profile depth, i.e. its
maximum chord length.
[0029] The airfoil 5 extends along the so called span (dash dotted
line in FIG. 1) between the root portion 3 and the tip 2. It can be
notionally subdivided into an outer, thin airfoil portion 6 and an
inner, thick airfoil portion 7. As the border between the thin
airfoil portion and the thick airfoil portion is not commonly
defined, the present invention regards an airfoil portion as to be
thick if the ratio of its thickness to the chord length is above
30%.
[0030] A chord-wise cross-section through the rotor blades thin
airfoil portion 6 along the line I-I is shown in FIG. 2. The
aerodynamic profile of the airfoil portion shown in FIG. 2
comprises a convex suction side 13 and a less convex pressure side
15. The dash-dotted line extending from the blades leading edge 9
to its trailing edge 11 shows the chord of the profile. Although
the pressure side 15 comprises a convex section 17 and a concave
section 19 in FIG. 2, it may be implemented without a concave
section at all as long as the suction side 13 is more convex than
the pressure side 15.
[0031] A chord-wise cross-section through the rotor blades thick
airfoil portion 7 along the line II-II in FIG. 1 is shown in FIG. 3
for a first embodiment of the invention. The general shape of the
thick airfoil portions cross-section corresponds to the general
shape of the thin airfoil portions cross-section and will therefore
not be described in detail again. In addition, elements of the
cross-section shown in FIG. 3 corresponding to elements shown in
the cross-section of FIG. 2 are designated with the same reference
numerals.
[0032] The main difference between the cross-section of the thick
airfoil portion shown in FIG. 3 and the cross-section of the thin
airfoil portion shown in FIG. 2 is that the ratio between the
highest thickness of the profile, as defined as to the longest
straight line from the suction side 13 to the pressure side 15
perpendicular to the chord, and the chord length of the profile is
above 30% whereas the respective ratio of the profile shown in FIG.
2 is below 30%.
[0033] Also shown in the thick airfoil portion's cross-section
according to the first embodiment is a vortex generator 21 which is
located at the suction side 13 between 25 and 30% chord length, as
measured from the leading edge 9.
[0034] Alternative locations of the vortex generators 21', 21'' on
the suction side 13 of the thick airfoil portion are shown in FIGS.
4 and 5. Except for the location of the vortex generators, the
shape of the cross-sections shown in FIGS. 3 to 5 are identical. In
the cross-section shown in FIG. 4, the vortex generator 21' is
located at about 18% to 22% chord length whereas the vortex
generator 21'' in the cross-section shown in FIG. 5 is located
between 8% and 12% chord length.
[0035] It should be noted that the optimum position of the vortex
generator may vary depending on the thickness to chord length ratio
of the profile as well as on the overall shape of the
cross-section. However, it is advantageous if the vortex generator
lies in the range between 5% and 30% of the chord length for thick
airfoil portions with a ratio of thickness to chord length in the
range between 30% and 80% and in particular for ratios in the range
between 40% and 65%.
[0036] The influence of the vortex generators 21, 21', 21''' at the
locations shown in FIGS. 3 to 5 on the lift of the wind turbine
blade 1 is shown in FIG. 6. The figure shows the lift coefficient
c.sub.l of the turbine blade 1 as a function of the angle of attack
(AOA) of the wind, i.e. the angle between the chord and the
relative wind seen from leading edge 9 of the rotor blade 1. In
general, a higher lift coefficient increases the efficiency of the
turbine blade.
[0037] The line denoted by A is the result of a lift coefficient
measurement for a wind turbine blade without any vortex generators.
The lines designated by B, C and D show the results of turbine
blades having vortex generators at the suction side of the thick
airfoil portion at the locations shown in FIG. 3 (B), in FIG. 4 (C)
and in FIG. 5 (D). Except for the presence and the location of the
vortex generators, respectively, all four turbine blades are
identical.
[0038] It can be easily seen from FIG. 6 that the presence of the
vortex generators in the thick airfoil portion increases the lift
coefficient as soon as the wind angle of attack is higher than
about 3 degree. With higher angles of attack the lift coefficients
of the different wind turbine rotor blades merge again. For the
rotor blade B having vortex generators as shown in FIG. 3 the lift
coefficient c.sub.l is more or less identical with the rotor blade
A without any vortex generators for angles of attack greater than
about 15 degree. For wind turbine rotor blades C having vortex
generators at the location shown in FIG. 4 the lift coefficient
c.sub.l is more or less identical with the rotor blade A without
vortex generators for angles of attack higher than about 18 degree.
With the vortex generators in the location shown in FIG. 5 the lift
coefficient c.sub.l of the wind turbine rotor blade is
significantly higher than the lift coefficient of the rotor blade A
without vortex generators in a broad range of angle of attack,
namely between about 3 degrees and 23 degree. Therefore, blade D
represents a particularly advantageous embodiment of the
invention.
[0039] As a general trend it can be noted that the maximum lift
coefficient of the blade moves towards higher angles of attack as
the location of the vortex generators moves towards the leading
edge of the profile. Moreover, the maximum value of the lift
coefficient c.sub.l increases accordingly.
[0040] FIG. 7 shows the drag coefficient c.sub.d for the four
blades shown in FIG. 6. The differences in the drag coefficient
c.sub.d between the four turbine blades A, B, C, D are less
prominent than the differences between the lift coefficients
c.sub.l. While the lift coefficients c.sub.l differ strongly
between the different blades in the range from 3 degree AOA to the
range of 23 degree AOA larger differences between the drag
coefficients of the blades can only be seen from about 3 degree AOA
to about 12 degree AOA. The reduction of drag in this range for the
rotor blades with vortex generators results from a delay in stall
caused by the vortex generators.
[0041] Based on the differences in the lift coefficients c.sub.l
and the drag coefficient c.sub.d for the different vortex generator
configurations shown in FIGS. 3 to 5 an annual energy production
(AEP) has been calculated. Compared to the turbine blade without
vortex generators (blade A) the annual energy production can be
increased by almost one percent for the vortex generator
configuration shown in FIG. 3, by almost 1.5 percent for the vortex
generator configuration shown in FIG. 4 and by more than 1.7
percent for the vortex generator configuration shown in FIG. 5.
[0042] Although the main advantage of the vortex generators is an
improved energy production, other advantages are achievable, too.
The drop of lift, as represented by the drop of the lift
coefficient c.sub.l in FIG. 6, has importance for the loads on the
tower. By moving the drop to other angles of attack it is possible
to influence the dynamical loading of the tower. Furthermore, by
delay in stall, as has been discussed with reference to FIG. 7, the
noise produced by the rotor may be reduced.
* * * * *