Source: https://patents.google.com/patent/US8834130
Timestamp: 2018-03-24 02:29:40
Document Index: 82439539

Matched Legal Cases: ['Application No. 08388014', 'art 33', 'art 35', 'art 33', 'art.\n3', 'art.\n9', 'art.\n10', 'art.\n11', 'art.\n12']

US8834130B2 - Wind turbine blade with an auxiliary airfoil - Google Patents
Wind turbine blade with an auxiliary airfoil Download PDF
US8834130B2
US8834130B2 US12935424 US93542409A US8834130B2 US 8834130 B2 US8834130 B2 US 8834130B2 US 12935424 US12935424 US 12935424 US 93542409 A US93542409 A US 93542409A US 8834130 B2 US8834130 B2 US 8834130B2
US12935424
US20110020128A1 (en )
A blade for a rotor of a wind turbine having a substantially horizontal rotor shaft, the rotor comprising a hub, from which the blade extends substantially in a radial direction when mounted to the hub. The blade comprises a main blade part having a profiled contour comprising a pressure side and a suction side as well as a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge. The profiled contour generates a lift when being impacted by an incident airflow. The profiled contour is divided in the radial direction into a root region with a substantially circular or elliptical profile closest to the hub, the substantially circular or elliptical profile having a diameter, an airfoil region with a lift generating profile furthest away from the hub, and a transition region between the root region and the airfoil region. The profile of the transition region gradually changes in the radial direction from the circular or elliptical profile of the root region to the lift generating profile of the airfoil region. The blade further comprises a first auxiliary airfoil having a first pressure side and a first suction side as well as a first chord extending between a first leading edge and a first trailing edge. The first chord has a length that is 75% or less of the diameter of the substantially circular or elliptical profile in the root region and the first auxiliary airfoil is arranged so that it extends in the radial direction along at least a part of the root region of the main blade part with a distance there between.
This is a National Phase Application filed under 35 USC 371 of International Application No. PCT/EP2009/053941, filed on Apr. 2, 2009, an application claiming foreign priority benefits under 35 USC 119 of European Application No. 08388014.6, filed on Apr. 2, 2008, the content of each of which is hereby incorporated by reference in its entirety.
It is well known from the aeroplane industry that aeroplanes built with two wings, so called biplanes, normally can lift more than an aeroplane with only one wing. This allows for an increase of the total lift of the wings of the aeroplane without increasing the width of the wings. This principle of using two blades is also known in connection with blades for wind turbines, e.g. by manufacturing wind turbines with two or more rotors. As an example, JP56138465A2 discloses an auxiliary propeller for a wind turbine, where the auxiliary propeller is mounted on the same rotor as a main propeller. The auxiliary propeller has a larger pitch angle than the main propeller, such that the auxiliary propeller accelerates the rotor smoothly at low wind speed, while at high wind speed, the auxiliary propeller decelerates the rotor. Thus the auxiliary propeller works as a speed control system of the rotor.
A similar idea is described in WO 2007/045244 by the present applicant, where the circular root region and the transition region are replaced by two blade segments having a lift-generating airfoil profile.
CA 2 425 447 discloses a wind turbine blade unit comprising two blades disposed in a canard type configuration, i.e. a smaller airfoil arranged in front of a larger airfoil. This configuration provides a passive solution for self-adjusting the pitch angle of the wind turbine blade so as to control the wind turbine rotor hub rotation speed.
WO 02/055884 discloses a rotor for a water turbine or a water pump, the rotor comprising a number of vanes having a main vane blade and a secondary vane blade. The distance between the main vane blade and the secondary vane blade may be adjustable.
The pressure side and the suction side at the transition region and the root region are defined from the pressure side and the suction side at the airfoil region, thus the pressure side and the suction side extends (or continues) from the airfoil region into the transition region and the root region. The blade may be twisted, i.e. the chord varies angularly in the radial direction. The distance between the main blade part and the first auxiliary airfoil may vary along the radial direction.
In principle, it may sometimes be difficult to determine where the root region ends and the transition region begins. Thus, when stating that the root region comprises a substantially circular or elliptical profile, it does not exclude that the root region or the transition region also may comprise a substantially oval or egg-shaped profile. Thus, diameter in the context of the present invention means the diameter of the circular profile or the length of the major axis of the elliptical profile or the chord of the profile in the root region.
In another embodiment according to the invention, the blade is adapted for use in a wind turbine rotor having a direction of rotation during normal operation, and wherein a number of auxiliary airfoils is arranged in the radial direction along at least a part of the root region, so that said number of auxiliary airfoils increase lift and/or decrease drag on the root region and/or the transition region of the main blade part. This can for instance be achieved by arranging the auxiliary airfoils in such a way that the auxiliary airfoils alter and guide the flow around the root region in such a way that the drag is reduced and/or lift is increased. However, the drag on the root region of the main blade part may also increase or even be unchanged for certain flow configurations, especially if the lift is increased.
Advantageously, the first auxiliary airfoil extends along at least 50% of a radial extent of the root region of the blade. Thus, the auxiliary airfoil improves the aerodynamic condition of a large part of the root region. The airfoil may also extend along at least 60%, 70% or 75% of the root region.
According to another advantageous embodiment, the first auxiliary airfoil is arranged so that it does not extend into or beyond an outboard part of the transition region, the outboard part corresponding to 25% of the radial extent of the transition region nearest the airfoil region. In other words, the auxiliary airfoil extends at the most along the inner 75% of the transition region, i.e. the part nearest the root region or nearest the hub. According to other embodiments, the outboard part corresponds to 30%, 40%, or 50% of the radial extent of the transition region.
In another embodiment according to the invention, the first suction side of the first auxiliary airfoil faces towards the pressure side of the main blade part. Advantageously, the first auxiliary airfoil is arranged near the trailing edge of the main blade part, wherein the first chord of the first auxiliary airfoil, when seen from the leading edge towards the trailing edge of the first auxiliary airfoil, is tilted towards the pressure side of the main blade part.
In another embodiment according to the invention, the first pressure side of the first auxiliary airfoil faces towards the pressure side of the main blade part. Advantageously, the first auxiliary airfoil is arranged near the trailing edge of the main blade part, wherein the first chord of the first auxiliary airfoil, when seen from the leading edge towards the trailing edge of the first auxiliary airfoil, is tilted towards the suction side of the main blade part.
The root region and transition region typically has a total length corresponding to 10%-20% of the total extent of the blade.
In another embodiment according to the invention, the first auxiliary airfoil and the main blade part are integrally formed. The first auxiliary airfoil and the main blade part may be formed as a single shell body, which may contribute further to strengthening the blade. However, preferably, the first auxiliary airfoil and the main blade part are separate elements. Thus, the two blade part may be manufactured separately, and the auxiliary airfoil be fitted to the main blade part afterward manufacturing the two blade parts.
Thus, according to another aspect, the invention provides a method of retrofitting a first auxiliary airfoil to a wind turbine blade having a profiled contour comprising: a pressure side and a suction side as well as a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, the profiled contour generating a lift when being impacted by an incident airflow, wherein the profiled contour in the radial direction is divided into: a root region with a substantially circular or elliptical profile, the substantially circular or elliptical profile having a diameter, an airfoil region with a lift generating profile, and a transition region between the root region and the airfoil region, the profile of the transition region gradually changing in the radial direction from the circular or elliptical profile of the root region to the lift generating profile of the airfoil region. The first auxiliary airfoil is arranged so that it extends in the radial direction along at least a part of the root region and/or the transition region of the main blade part with a distance there between, wherein the first auxiliary airfoil has a first chord having a length that is 75% or less of the diameter of the substantially circular or elliptical profile in the root region.
FIG. 11 shows a cross sectional view of an egg-shaped profile with a first auxiliary airfoil and a second auxiliary airfoil.
FIG. 1 illustrates a conventional modern upwind wind turbine 2 according to the so-called “Danish concept” with a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub 8 and three blades 10 extending radially from the hub 8, each having a blade root 16 nearest the hub 8 and a blade tip 14 furthest from the hub 8.
FIG. 2 shows a schematic view of an embodiment of a wind turbine blade comprising a main blade part. The wind turbine blade 10 has the shape of a conventional wind turbine blade and comprises a root region 30 closest to the hub, a profiled or an airfoil region 34 furthest away from the hub and a transition region 32 between the root region 30 and the airfoil region 34. The blade 10 comprises a leading edge 18 facing the direction of rotation of the blade 10, when the blade is mounted on the hub, and a trailing edge 20 facing the opposite direction of the leading edge 18. FIG. 2 depicts the blade as seen above the suction surface or side covering the airfoil region 34, the transition region 32 and the root region 30, while the pressure surface or side on the opposite side of the blade 10 is hidden.
An auxiliary airfoil 70′ is arranged along the root region 30 of the main blade part and an inboard part 33 of the transition region 32. Thus, the auxiliary airfoil 70′ does not extend into or beyond an outboard part 35 of the transition region 32. The outboard part may for instance extend along 25% of the total radial extent of the transition region 32. The auxiliary airfoil 70′ alters and improves the pressure distribution around the root region 30 and the inboard part 33 of the transition region 32 in order to increase the power production of a wind turbine utilising such blades and auxiliary airfoils.
FIG. 3 shows a schematic view of an airfoil profile 50 of a typical blade of a wind turbine depicted with the various parameters, which are typically used to define the geometrical shape of an airfoil. The airfoil profile 50 has a pressure side 52 and a suction side 54, which during use—i.e. during rotation of the rotor—normally face the windward side and the leeward side, respectively. The airfoil 50 has a chord 60 with a chord length c extending between a leading edge 56 and a trailing edge 58 of the blade. The airfoil profile 50 has a thickness t, which is defined as the distance between the pressure side 52 and the suction side 54. The thickness t of the airfoil profile 50 varies along the chord 60. The deviation from a symmetrical profile is given by a camber line 62, which is a median line through the airfoil profile 50. The median line can be found by drawing inscribed circles from the leading edge 56 to the trailing edge 58. The median line follows the centres of these inscribed circles and the deviation or distance from the chord 60 is called the camber f. The asymmetry can also be defined by use of parameters called the upper camber and lower camber, which are defined as the distances from the chord 60 and the suction side 54 and pressure side 52, respectively.
In the following with reference to FIGS. 4-8 a number of different embodiments are described with respect to a circular profile. However, the auxiliary airfoils may also be arranged at the similar positions of substantially elliptical, oval, or egg-shaped profiles as shown in FIG. 11. In all the embodiments shown in FIGS. 4-8 and FIG. 11, the inflow direction of an incident airflow is from the left towards the right side of the figures.
FIG. 4 shows a cross section through a blade according to the invention. A first auxiliary airfoil 70 and a second auxiliary airfoil 100 are mounted to a root region 90 having a circular profile via attachment means 110. The attachment means 110 in FIG. 4 are shown as struts; however these attachment means 110 may be constructed in many ways. As illustrated in FIG. 4, the first auxiliary airfoil 70 may shift orientation relative to the root region profile 90. The second auxiliary airfoil 100 in FIG. 4 may also shift orientation relative to the root region profile 90. In this embodiment the first suction side 74 of the first auxiliary airfoil 70 is facing the root region profile 90, while a first pressure side 102 of the second auxiliary airfoil 100 is facing the root region profile 90. The first auxiliary airfoil 70 and the second auxiliary airfoil 100 alters the flow around the root region profile 90 such that the overall aerodynamic efficiency is improved, mainly by generating lift and/or reducing drag by altering the pressure distribution around the root region 90 in order to increase the lift component, e.g. by delaying separation and reducing drag. Further, the lift from the auxiliary airfoils may increase the overall lift.
However, the auxiliary airfoils can also improve the pressure distribution around substantially elliptical, oval, or egg-shaped profiles as shown in FIG. 11.
In the embodiment shown in FIG. 7 a first auxiliary airfoil with a first auxiliary airfoil profile 70 is arranged in such a way that the first pressure side 72 of the first auxiliary airfoil is facing the suction side 54 of the root region 90. Furthermore, a second auxiliary airfoil with a second auxiliary airfoil profile 100 is arranged in such a way that the second pressure side of the second auxiliary airfoil is facing the pressure side 52 of the root region profile 90. The first auxiliary airfoil and the second auxiliary airfoil in combination alter the flow around the root region profile 90, such that drag is lowered by reducing the separation of airflow in the region between the auxiliary airfoils.
FIG. 9 shows a schematic view of a flow around a circular profile, where an angle v is defined. In FIG. 10 graph 1 and graph 3 show the pressure coefficient distributions as a function of v for flow around the circular profile, where graph 1 is a theoretically obtained inviscid solution of the flow and graph 3 is an experimental result for flow with a supercritical Reynolds number. Graph 2 shows the pressure coefficient distribution as a function of v for flow around a circular profile with two auxiliary airfoils arranged so the configuration corresponds to the configuration shown in FIG. 7, while graph 4 shows the pressure coefficient distribution as a function of v for flow around a circular profile with two auxiliary airfoils arranged so the configuration corresponds to the configuration shown in FIG. 8.
The first derivative of each graph 1-4, shown in FIG. 10, corresponds to a pressure gradient; a high first derivative in absolute number thus corresponds to a high pressure gradient which leads to a faster boundary layer separation. This effect can be seen by considering graphs 1 to 4, where a high pressure gradient (steep slope) leads to a pressure coefficient plateau in the interval −60°<v<60°, which is lower than the pressure coefficient plateau in the interval −60°<v<60° for graphs with a lower pressure gradient. The lower the pressure coefficient plateau in the interval −60°<v<60°, the larger the overall pressure difference or drag. As seen in FIG. 10, one of the configurations with the circular profile combined with two auxiliary airfoils (graph 2) yields a lower drag than the drag measured experimentally on the circular profile alone (graph 3). This clearly indicates that the auxiliary airfoils in this embodiment increase the overall aerodynamically efficiency.
110 attachment means
a profiled contour (50) comprising a pressure side (52) and a suction side (54) as well as a leading edge (56) and a trailing edge (58) with a chord (60) extending between the leading edge (56) and the trailing edge (58), the profiled contour (50) generating a lift when being impacted by an incident airflow, wherein the profiled contour (50) in the radial direction is divided into:
a root region (30) consisting of a substantially circular or elliptical profile (90) closest to the hub (8), the substantially circular or elliptical profile (90) along the entire root region having a diameter (D),
an airfoil region (34) with a lift generating profile furthest away from the hub (8), and
a transition region (32) between the root region (30) and the airfoil region (34), the profile of the transition region (32) gradually changing in the radial direction from the circular or elliptical profile (90) of the root region (30) to the lift generating profile of the airfoil region (34), characterized in that the blade (10) further comprises:
a first auxiliary airfoil (70) having a first pressure side (72) and a first suction side (74) as well as a first chord (76) extending between a first leading edge (78) and a first trailing edge (80), the first chord (76) having a length that is 75% or less of the diameter (D) of the substantially circular or elliptical profile (90) in the root region (30),
the first auxiliary airfoil (70) being arranged so that it extends in the radial direction along at least a part of the root region (30) and/or the transition region (32) of the main blade part with a distance there between.
2. The blade (10) according to claim 1, wherein the blade (10) is adapted for use in a wind turbine rotor having a direction of rotation during normal operation, and wherein a number of auxiliary airfoils (70, 100) is arranged in the radial direction along at least a part of the root region (30) and adapted so as to alter and guide the incident airflow so as to increase lift and/or decrease drag on the root region (30) and/or the transition region (32) of the main blade part.
3. The blade (10) according to claim 1, wherein a number of auxiliary airfoils (70, 100) is arranged in the radial direction along at least a part of the root region (30) and adapted so as to alter and guide the incident airflow so that the ratio between a lift coefficient and a drag coefficient for the root region (30) and/or the transition region (32) of the main blade part is increased.
4. The blade according to claim 1, wherein the first auxiliary airfoil (70) extends along at least 50% of a radial extent of the root region (30) of the blade.
5. The blade according to claim 1, wherein the first auxiliary airfoil (70) is arranged so that it does not extend into or beyond an outboard part of the transition region (32), the outboard part corresponding to 25% of the radial extent of the transition region (32) nearest the airfoil region (34).
6. The blade (10) according to claim 1, wherein the first auxiliary airfoil (70) extends along the root region (30) of the blade only.
7. The blade (10) according to claim 1, wherein the first chord length being 10-75% of the diameter (D), or 10-70%, or 10-60% or even 10-50%.
8. The blade (10) according to claim 1, wherein the first pressure side (72) of the first auxiliary airfoil (70) faces towards the suction side (54) of the main blade part.
9. The blade (10) according to claim 1, wherein the first suction side (74) of the first auxiliary airfoil (70) faces towards the pressure side (52) of the main blade part.
10. The blade (10) according to claim 1, wherein the first pressure side (72) of the first auxiliary airfoil (70) faces towards the pressure side (52) of the main blade part.
11. The blade (10) according to claim 1, wherein the position and/or
orientation of the first auxiliary airfoil (70) can be shifted relative to the main blade part.
12. The blade according to claim 1, wherein the first auxiliary airfoil (70) is attached to the main blade part by means of attachment means (110), such as struts.
13. The blade (10) according to claim 1, wherein the first auxiliary airfoil (70) is twisted along the radial direction.
14. The blade (10) according to claim 1, wherein a second auxiliary airfoil (100) is arranged so that it extends in the radial direction along at least a part of the root region (30) and/or the transition region (32) of the main part with a distance there between.
15. A wind turbine (2) including a rotor comprising a number of blades (10), preferably two or three, according to claim 1.
a pressure side and a suction side as well as a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, the profiled contour generating a lift when being impacted by an incident airflow, wherein the profiled contour in the radial direction is divided into:
a root region with a substantially circular or elliptical profile, the substantially circular or elliptical profile having a diameter along the entire root region,
an airfoil region with a lift generating profile, and
a transition region between the root region and the airfoil region, the profile of the transition region gradually changing in the radial direction from the circular or elliptical profile of the root region to the lift generating profile of the airfoil region, characterized by
arranging the first auxiliary airfoil so that it extends in the radial direction along at least a part of the root region and/or the transition region of the main blade part with a distance there between, and wherein the first auxiliary airfoil has a first chord having a length that is 75% or less of the diameter of the substantially circular or elliptical profile in the root region.
US12935424 2008-04-02 2009-04-02 Wind turbine blade with an auxiliary airfoil Active 2031-11-11 US8834130B2 (en)
EP08388014 2008-04-02
US20110020128A1 true US20110020128A1 (en) 2011-01-27
US8834130B2 true US8834130B2 (en) 2014-09-16
US12935424 Active 2031-11-11 US8834130B2 (en) 2008-04-02 2009-04-02 Wind turbine blade with an auxiliary airfoil
EP0064742A2 (en) 1981-05-07 1982-11-17 Ficht GmbH Rotor for a wind power station
JPS61167175A (en) 1985-01-18 1986-07-28 Mitsubishi Heavy Ind Ltd Propeller for windmill
JPH06159222A (en) 1992-06-23 1994-06-07 Nippon C-Futei Kk Windmill
WO2002055884A1 (en) 2001-01-10 2002-07-18 Voith Siemens Hydro Power Generation Gmbh & Co. Kg Rotor for a water turbine or water pump
US20100209257A1 (en) 2010-08-19 Wind turbine blade with submerged boundary layer control means
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:FUGLSANG, PETER;BOVE, STEFANO;SIGNING DATES FROM 20140817 TO 20140821;REEL/FRAME:034288/0681