WIND POWER INSTALLATION

Abstract

The present disclosure relates to a wind power installation having an aerodynamic rotor with at least one rotor blade, wherein the rotor blade has an active flow control device, which is designed to actively influence a flow over the rotor blade, wherein the flow control device comprises an opening in a rotor blade surface, referred to as a rotor blade surface opening, wherein the flow control device is configured to draw off and/or blow out air through the rotor blade surface opening air by way of a controllable air flow, wherein the wind power installation has a controller which is configured to control an amount of the controllable air flow through the rotor blade surface opening according to at least one of the following rules: if a rotational speed threshold value of a rotational speed of the rotor is exceeded, increasing the maximum controllable air flow successively with increasing rotational speed, if a torque threshold value of a torque of the rotor is exceeded, increasing the maximum controllable air flow successively with increasing torque.

Claims

1. A wind power installation comprising: an aerodynamic rotor and a rotor blade coupled to the aerodynamic rotor, and a flow control device on the rotor blade, wherein the flow control device is configured to actively influence a flow over the rotor blade, wherein the flow control device comprises a rotor blade surface opening, wherein the flow control device is configured to draw off air or blow out air or both through the rotor blade surface opening by way of a controllable air flow, wherein the wind power installation has a controller configured to control an amount of the controllable air flow through the rotor blade surface opening according to at least one of the following rules: if a rotational speed threshold value of a rotational speed of the rotor is exceeded, increasing a maximum controllable air flow successively with increasing rotational speed; and if a torque threshold value of a torque of the rotor is exceeded, increasing the maximum controllable air flow successively with increasing torque.

2. The wind power installation as claimed in claim 1, wherein the flow control device comprises a plurality of rotor blade surface openings along a length of the rotor blade, wherein the flow control device is configured to vary an amount of the air flow through the rotor blade surface openings along the length of the rotor blade.

3. The wind power installation as claimed in claim 2, wherein the controller is configured to control the amount of the controllable air flow through the rotor blade surface openings such that the amount of the air flow decreases over the length of the rotor blade.

4. The wind power installation as claimed in claim 3, wherein the controller is configured to control the amount of the controllable air flow through the rotor blade surface openings such that the decrease in the amount over the length of the rotor blade decreases with lower air density.

5. The wind power installation as claimed in claim 3, wherein the controller is configured to control the amount of the controllable air flow through the rotor blade surface openings in a manner dependent on a turbulence intensity, such that the decrease in the amount over the length of the rotor blade length increases with lower turbulence intensity.

6. The wind power installation as claimed in claim 1, wherein the controller is configured to control the amount of the controllable air flow through the rotor blade surface opening in a manner dependent on an air density.

7. The wind power installation as claimed in claim 1, wherein the controller is configured to vary an amount of the air flow through the rotor blade surface opening in a manner dependent on an azimuth angle of the rotor.

8. The wind power installation as claimed in claim 7, wherein the controller is configured to control the amount of the air flow through the rotor blade surface opening cyclically over the azimuth angle such that an amount of the air flow through the rotor blade surface opening is greater at an azimuth position of the rotor blade at the 12 o'clock position, than at the azimuth position at the 6 o'clock position.

9. The wind power installation as claimed in claim 1, wherein the rotor blade surface opening of the flow control device is formed such that an air flow exits or flows in substantially parallel to the rotor blade surface.

10. The wind power installation as claimed in claim 1, wherein the air flow through the rotor blade surface opening of the flow control device is controlled via a flow speed and/or a blowing-out or drawing-off rate.

11. The wind power installation as claimed in claim 10, wherein the blowing-out or drawing-off rate is determined as a product of a surface porosity and a quotient of mean blowing-out or drawing-off speed over the rotor blade surface opening and a relative incident flow speed of an undisturbed flow.

12. The wind power installation as claimed in claim 1, wherein the rotor blade surface opening includes a plurality of sub-openings distributed over the length of the rotor blade.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0038] Further advantages and preferred configurations will be described below with reference to the appended figures. In the figures:

[0039] FIG. 1 shows schematically and by way of example a wind power installation,

[0040] FIG. 2 shows schematically and by way of example a rotor blade,

[0041] FIG. 3 shows schematically and by way of example a result of an implementation in the controller,

[0042] FIG. 4 shows schematically and by way of example a result of an implementation in the controller, and

[0043] FIG. 5 shows schematically and by way of example a result of an implementation in the controller.

DETAILED DESCRIPTION

[0044] FIG. 1 shows a schematic illustration of a wind power installation according to the disclosure. The wind power installation 100 has a tower 102 and a nacelle 104 on the tower 102. An aerodynamic rotor 106 having three rotor blades 108 and having a spinner 110 is provided on the nacelle 104. During the operation of the wind power installation, the aerodynamic rotor 106 is set in rotational motion by the wind and thereby also rotates an electrodynamic rotor or runner of a generator, which is coupled directly or indirectly to the aerodynamic rotor 106. The electric generator is arranged in the nacelle 104 and generates electrical energy. The operation of the wind power installation 100 is controlled by a controller 112. The controller 112 may be implemented completely or partially within the nacelle 104, the tower 102, or else at a distance from the wind power installation 100, for example in a central wind farm controller of a wind farm.

[0045] FIG. 2 shows a schematic illustration of a rotor blade 108 of the wind power installation 100 in FIG. 1. The rotor blade 108 extends from a rotor blade root 114 to a rotor blade tip 116 in a rotor blade longitudinal direction L. The length of the rotor blade 108 in the rotor blade longitudinal direction is also referred to as the radius R, due to the use in the rotor 106.

[0046] In the region of the rotor blade root 114, provision is made of a blade connector 118 for connecting the rotor blade 108 to a rotor blade hub of the rotor 106. The pitch angles of the rotor blades 108 can be varied by pitch motors for example at the rotor blade roots 114 of the respective rotor blades 108.

[0047] Along the rotor blade longitudinal direction L, the rotor blade 108 has different aerodynamic profiles at radius positions r. Each aerodynamic profile extends from a point on the leading edge 120 to a point on the trailing edge 122, which are connected to one another via a suction side 124 and an opposite pressure side 126. At the leading edge 120, the air flow is divided into two partial flows over the suction side 124 and the pressure side 126.

[0048] The trailing edge 122 has a blunt trailing edge portion 122a in a region close to the hub and a sharp trailing edge portion 122b in a region close to the rotor blade tip 116. The thickness of the trailing edge 122 decreases substantially in the rotor blade longitudinal direction L.

[0049] FIG. 2 also shows a flow control device 128, which is designed to actively influence a flow over the rotor blade 108. The flow control device 128 comprises multiple rotor blade surface openings 130, which are formed as openings and which, in this example, are arranged at different radius positions in the rotor blade longitudinal direction L and have substantially a rectangular cross section. The flow control device 128 may have one or more fans associate therewith. The one or more fans may be inside the rotor blade 108 and are coupled to the controller 112 and actively controlled by the controller. The fans are able to blow or suction the air and have adjustable speeds that may be controlled by the controller. In another embodiment, plasma actuators may be used to control the aerodynamic flow using a high-voltage AC signal. In yet another embodiment, the size of the openings may be changes using shape memory alloys. For instance, one possibility of controlling fluid output into a boundary layer is also described in EP2771239 (which also published as U.S. Pat. Pub. No. 2014/284430), which is incorporated by reference in its entirety. The flow control device is configured to draw off and/or blow out air through the rotor blade surface opening 130 by way of a controllable air flow.

[0050] The rotor blade surface openings 130 may have any shape and be arranged on the suction side 124 and/or on the pressure side 126 at any positions and in any number. Combinations of different shapes or a single rotor blade surface opening 130 are/is also conceivable.

[0051] The disclosure lies in the actuation and regulation of the air flow, which is blown out and/or drawn off by fans through the rotor blade surface opening 130 by means of the flow control device 128. The blowing-in or drawing-off results in the generation of longitudinal vortices at the rotor blade surface openings 130, which longitudinal vortices lead to an increase in the flow speeds near the wall and thus to a stabilization of the boundary layer flow with respect to flow separation. The advantage of these active flow control measures is that the blowing-out or the drawing-off of the air can be activated or deactivated, that is to say is realized as required. Accordingly, the stabilization of the flow with respect to separation is carried out only if it is necessary due to the prevailing boundary conditions. This is refrained from in other cases, in order then not to have to accept any power-reducing effects of the control measure. With this procedure, it is thus possible for the installation yield to be further increased overall.

[0052] Some examples for the regulation of the flow control device 128 by the controller 112, which lead to an optimization of the installation yield, are discussed by way of example below with reference to FIGS. 3 to 5. The effectiveness of the active control measure by means of the flow control device 128 is characterized here via an amount of the maximum controllable air flow through the rotor blade surface opening 130 or via an amount of the maximum wall-normal speed above the rotor blade surface opening 130. A positive value corresponds to a maximum air flow/wall-normal speed of blowing-out, and a negative value corresponds to a maximum drawing-off rate/drawing-off speed, which would be established in the rotor blade surface opening 130. Generally, it may be assumed to a certain extent that, with increasing amount of the maximum air flow or speed in the rotor blade surface opening 130, it is also the case that an increasing stabilizing effect is established, that is to say flow separation on the rotor blade can be prevented. For rotor blade surface openings 130 which allow blowing-out which takes place normal to the surface, the consideration of the air flow can be transferred easily into the maximum wall-normal speed. Differences are obtained in particular if the geometry of the rotor blade surface opening 130 gives rise to a significant tangential flow component through the rotor blade surface opening 130. In particular for these cases, the embodiments described below by way of example for the maximum wall-normal speed may be correspondingly generalized to the maximum controllable air flow.

[0053] FIG. 3 shows schematically and by way of example a preferred implementation in the controller 112, wherein there is plotted a profile of the maximum wall-normal speed |.sub.max| on the y-axis over the installation rotational speed n or the installation torque M. The amount of the maximum wall-normal speed |.sub.max| increases with increasing rotational speed n, since in a part-load range 302, it is often the case that no flow separation is expected, intervention of a control measure is not required and the maximum power coefficient and yield can be realized with the rotor blade 108. With increasing wind speed and rotational speed n, the risk of highly power-reducing flow separation on the rotor blade, and thus the requirement for flow control, is increased. Therefore, the maximum wall-normal speed is correspondingly increased successively with increasing rotational speed n from a threshold value 304 of the rotational speed n up to the maximum rotational speed n.sub.max.

[0054] The profile of the ascent of the maximum wall-normal speed |.sub.max| from the threshold value 304 of the installation rotational speed n differs in a manner dependent on further operating parameters or ambient parameters and may for example be a linearly ascending profile 306, a bounded profile 308 or an exponential profile 310.

[0055] FIG. 4 shows schematically and by way of example the profile of the maximum wall-normal speed |.sub.max| over the rotor radius r/R, normalized with respect to the maximum radius R, in each case for two air densities .sub.1, .sub.2 or two turbulence intensities TI.sub.1, TI.sub.2 of the incident flow at constant installation rotational speed n. One profile 402 is associated with the air density .sub.1 and the turbulence intensity TI.sub.1. One profile 404 is associated with the air density .sub.2 and the turbulence intensity TI.sub.2.

[0056] In this example, as mentioned for constant rotational speed n, it holds that .sub.1>.sub.2 and/or TI.sub.2>TI.sub.1. This means that the lower the air density or the higher the turbulence intensity of the incident flow, the further outward, that is to say the greater r/R is, the flow around the rotor blade has to be controlled, that is to say the amount of the maximum wall-normal speed |.sub.max| in the rotor blade surface opening 130 assumes a value greater than zero. The amount of the maximum wall-normal speed |.sub.max| is greater than zero up to a radius position 406 for the profile 402, and correspondingly up to a radius position 408, which is closer to the rotor blade tip than the radius position 406, for the profile 404. The amount of the maximum wall-normal speed |.sub.max| correspondingly decreases from a global maximum in the region of the rotor blade root more slowly for the profile 404 than for the profile 402. Although a linear profile 404, 402 is shown, other decreasing profiles with respect to the radius position are also possible in this regard.

[0057] At many locations, an installation is subjected to a possibly highly varying turbulence intensity TI and/or, due to seasonal variations in the mean temperature, varying air densities p too. The control measure for controlling separation is activated radially on the rotor blade 108 toward the blade tip only as far as necessary, according to the ambient conditions.

[0058] For identical turbulence intensity TI, it is for example the case that control in winter can be activated only up to relatively small radius positions r/R compared with in summer, during which the air densities are reduced compared with winter. A similar situation applies to the influence of the turbulence intensity TI. In this regard, many locations are subjected diurnally, that is to say within 24 hours, to a day/night cycle with negligible variation in air density in which a higher turbulence intensity TI in the incident flow for the wind power installation 100 prevails during solar exposure in the daytime than at night, during which the turbulence intensity TI is significantly lower. This diurnal variation would be handled by the regulation by way of the controller 112 such that the flow control is activated toward greater radius positions r/R in the daytime, with high turbulence intensity TI, than at night, when the turbulence intensity TI decreases. These are just two examples of how the factors air density and turbulence intensity TI advantageously influence the regulation of an active flow control measure 128 at the rotor blade 108 in order to prevent, as far as possible, separation of the flow passing around the rotor blade.

[0059] Finally, FIG. 5 shows schematically and by way of example the amount of the maximum wall-normal speed |.sub.max| in the rotor blade surface opening 130 over the rotor azimuth co at constant rotational speed n illustrated for different vertical shears .sub.1, .sub.2 of the bottom boundary layer of the incident flow.

[0060] Different shears of the bottom boundary layer often reoccur diurnally at a wind power installation 100. For high positive shear, for .sub.2 in the example in FIG. 5, the wind speed is in this case possibly significantly higher at relatively large distances from the bottom than close to the bottom. In FIG. 5, a profile of the maximum wall-normal speed |.sub.max| for relatively lower shear .sub.1 in comparison with a profile 502 is illustrated, while a profile 504 for a relatively large shear .sub.2, .sub.2>.sub.1 is illustrated.

[0061] Thus, when the rotor blade is in the so-called 12 o'clock position, that is to say the position at which the blade tip is at the greatest distance from the bottom, or in other words at 0 rotor azimuth , then the rotor blade 108, in this position, is normally subjected to higher wind speeds .sub.w than in the 6 o'clock position, or at 180 rotor azimuth, when the blade tip is thus at the smallest distance from the bottom. This is manifested as a low point of the maximum wall-normal speed |.sub.max| for both profiles 502, 504 in a range 506.

[0062] The consequence of this is that, in the 12 o'clock position, greater angles of attack are present than in the 6 o'clock position. It is therefore preferable for the control measure to be activated in the 12 o'clock position, whereas this is not or is less necessary in the 6 o'clock position. This procedure is to be applied in a more pronounced manner, the higher the vertical shear is.

[0063] There is also the case in which negative vertical shears occur, in which therefore the wind speed decreases substantially with height. In this case, the control measure can then be activated in the 6 o'clock position, whereas this is not or is less necessary in the 12 o'clock position. In the case of negative vertical shears too, the procedure is to be applied in a more pronounced manner, the greater the shear is in terms of magnitude.

[0064] This procedure is also advantageously able to be applied in the case of horizontal shear. Pronounced horizontal shear may occur for example if a wind power installation 100 is situated with a part of its rotor disk in the wake of another wind power installation or some other obstacle. That part of the rotor disk which is situated in the wake is then subjected to lower wind speeds than that part of the rotor disk which is flowed against in an undisturbed manner.

[0065] In principle, a procedure such as that shown in FIG. 5 for vertical shear is expedient here, with the difference that, in the profile of the maximum wall-normal speed, a phase shift by 90 to the 3 o'clock or 9 o'clock position takes place.

[0066] One area of application is in particular rotor blades 108 at wind power installations 100 that have an active flow control system, for example the flow control device 128, with which, via openings in the rotor blade surface, air is blown into the boundary layer flow on the rotor blade, or drawn off through the openings, in a steady or unsteady manner. Here, the system is able to vary, in terms of amplitude and frequency, the speed of the air blown out or drawn off.

[0067] In at least one embodiment, a purpose is the optimization of yield of wind power installations by activation and active regulation of the flow control measure in the rotor blade boundary layer only when the stabilizing effect of said flow control measure is required in order to prevent highly power-reducing flow separation. If such an intervention is not required, the control measure is deactivated and has little to no damaging effect on the installation yield. The regulation of the control measure preferably takes into consideration here the wind field impinging on the wind power installation 100 and the parameters characterizing the wind field, such as turbulence intensity, vertical shear and horizontal shear, and air density, in order to determine optimum operating parameters for the flow control system, with the aim of avoiding flow separations on the rotor blade 108.

[0068] The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.