Acoustic damping system for a wind turbine tower

A system and method for reducing audible tonality of a wind turbine caused by vibrations generated by the drivetrain assembly thereof includes a plurality of damping elements mounted at a plurality of locations on an inner surface of a tower of the wind turbine. The plurality of locations have vibration levels above a predetermined threshold. Thus, during operation of the wind turbine, the damping elements are configured to damp vibrations of the tower so as to reduce noise generated thereby.

FIELD OF THE INVENTION

The present invention relates to generally to wind turbines, and more particularly, to a system and method for reducing audible tonality generated by a wind turbine.

BACKGROUND OF THE INVENTION

Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and a rotor having a rotatable hub with one or more rotor blades. The rotor blades capture kinetic energy of wind using known airfoil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.

Like most dynamic systems, wind turbines are subject to undesirable vibrations that may detrimentally impact the operation and/or structural integrity of the wind turbine. In addition, such vibrations may contribute to undesirable noise in the area surrounding the wind turbine. For example, vibrations generated by the drivetrain can be radiated as sound by the tower structure, thereby significantly contributing to an audible tonality in the vicinity of the wind turbine. This noise can be a nuisance to neighbors of the wind turbine as well as personnel working at the wind turbine site.

One design approach for minimizing vibrations in the wind turbine tower is to structurally reinforce the wind turbine so as to alter its vibration response (e.g., make the tower stiffer). Such a solution, however, may be prohibitively expensive, especially as tower heights continue to increase.

In view of the aforementioned, there is a need for an improved acoustic damping system for wind turbine towers. Accordingly, the present disclosure is directed to a system and method having a plurality of damping elements that reduce audible tonality generated by the wind turbine by reducing surface vibrations of the tower.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, the present disclosure is directed to a method for reducing audible tonality generated by a wind turbine. The method includes determining one or more locations on an inner surface of a tower of the wind turbine having vibration levels above a predetermined threshold. The method also includes mounting a damping element at each location above the threshold on the inner surface of the upper section of the tower of the wind turbine. Thus, during operation of the wind turbine, the damping elements are configured to damp vibrations of the tower so as to reduce audible tonality generated thereby. It should be understood that the damping elements may further include any of the additional features as described herein.

In one embodiment, the one or more locations may include an upper section of the inner surface of the tower. More specifically, in certain embodiments, the upper section of the tower may include from about 15% to about 40% of an overall height of the tower as measured from a top of the tower.

In another embodiment, the step of determining one or more locations on the inner surface of the tower of the wind turbine having vibration levels above a predetermined threshold may include measuring vibration levels at the one or more locations or determining, via computer simulation, the one or more locations as a function of at least one of a size or a location of the tower.

In another embodiment, the method may include selecting a modal mass of the mass element and a stiffness of the elastomeric element so as to set a target frequency of the damping element. In additional embodiments, the method may include omitting damping elements in locations containing flanges.

In further embodiments, the method may include spacing the plurality of damping elements evenly apart in a circumferential direction. In addition, the method may include spacing the plurality of damping elements in a vertical direction as a function of vibration levels on the inner surface of the tower.

In alternative embodiments, the method may include spacing the plurality of damping elements randomly on the inner surface of the tower.

In another aspect, the present disclosure is directed to a method for reducing audible tonality generated by a wind turbine. The method includes determining a vibration area on a tower of the wind turbine having vibration levels above a predetermined threshold. The method also includes mounting a plurality of damping elements within the vibration area of the tower of the wind turbine at or near antinode locations. Thus, during operation of the wind turbine, the damping elements are configured to damp vibrations of the tower so as to reduce audible tonality generated thereby.

In yet another aspect, the present disclosure is directed to a system for reducing audible tonality generated by a wind turbine. The system includes a plurality of damping elements mounted at a plurality of locations on an inner surface of a tower of the wind turbine, the plurality of locations having vibration levels above a predetermined threshold. Thus, during operation of the wind turbine, the plurality of damping elements are configured to damp vibrations of the tower so as to reduce audible tonality generated thereby.

In one embodiment, the vibrations of the tower (i.e. the surface vibrations) may be caused by a drivetrain assembly of the wind turbine. In such embodiments, the plurality of damping elements may be mounted on an upper section of the inner surface of the tower. More specifically, in certain embodiments, the upper section of the tower may include from about 15% to about 40% of an overall height of the tower as measured from a top of the tower. In other embodiments, the plurality of damping elements may be distributed over the entire tower surface.

In another embodiment, the plurality of damping elements are tuned-mass dampers. More specifically, in certain embodiments, each of the plurality of damping elements may include a mass element configured with an elastomeric element. Thus, in certain embodiments, the modal mass of the mass element and the stiffness of the elastomeric element may be selected to set the target frequency of the damping element.

In additional embodiments, the plurality of damping elements may be mounted on the inner surface of the tower via at least one of a magnet, one or more fasteners, or an adhesive. In embodiments utilizing magnets, the mass element, the elastomeric element, and the magnet may be secured together via a fastener through a central longitudinal axis.

In another embodiment, the plurality of damping elements may be spaced evenly apart in the circumferential or the horizontal direction. Further, spacing of the plurality of damping elements in the vertical direction may be determined as a function of vibration levels on the inner surface of the tower, e.g. as determined via simulation. Alternatively, the plurality of damping elements may be randomly spaced on the inner surface of the tower.

In still a further embodiment, the plurality of damping elements may have a frequency range of from about 80 Hertz (Hz) to about 800 Hz although it should be understood that any suitable broad frequency range may be selected so as to cover large parts of the wind turbine variable speed operation.

DETAILED DESCRIPTION OF THE INVENTION

Generally, the present disclosure is directed to a system and method for reducing audible tonality of a wind turbine caused by vibrations generated by the drivetrain assembly thereof. The system includes a plurality of damping elements mounted at a plurality of locations on an inner surface of a tower of the wind turbine, the plurality of locations having vibration levels above a predetermined threshold. Thus, during operation of the wind turbine, the plurality of damping elements are configured to damp vibrations of the tower so noise generated thereby.

The present disclosure provides many advantages not present in the prior art. For example, the damping system according to the present disclosure can be easily retro-fit to existing wind turbines. Further, the damping system of the present disclosure provides a cost-effective solution for improving acoustic efficiency of the turbine. Thus, by reducing tower vibrations, the damping system of the present disclosure reduces noise in the vicinity of the wind turbine. In addition, the damping system of the present disclosure covers a wide frequency range and thus works robustly over its lifetime without the need for additional maintenance and/or tuning.

The wind turbine10may also include a turbine control system or turbine controller26centralized within the nacelle16. In general, the turbine controller26may include a computer or other suitable processing unit. Thus, in several embodiments, the turbine controller26may include suitable computer-readable instructions that, when implemented, configure the controller26to perform various different functions, such as receiving, transmitting and/or executing wind turbine control signals. As such, the turbine controller26may generally be configured to control the various operating modes (e.g., start-up or shut-down sequences) and/or components of the wind turbine10. For example, the controller26may be configured to adjust the blade pitch or pitch angle of each rotor blade22(i.e., an angle that determines a perspective of the blade22with respect to the direction of the wind) about its pitch axis28in order to control the rotational speed of the rotor blade22and/or the power output generated by the wind turbine10. In addition, the turbine controller26may control the orientation of the nacelle16with respect to the wind direction58by transmitting suitable control signals to one or more yaw drive mechanisms60that engage a yaw bearing62(FIG. 2). Thus, rotation of the yaw bearing62changes the orientation of the nacelle16.

Referring now toFIG. 2, a simplified, internal view of one embodiment of the nacelle16of the wind turbine10shown inFIG. 1is illustrated. As shown, a generator24may be disposed within the nacelle16. In general, the generator24may be coupled to the rotor18for producing electrical power from the rotational energy generated by the rotor18. For example, as shown in the illustrated embodiment, the rotor18may include a rotor shaft32coupled to the hub20for rotation therewith. The rotor shaft32may, in turn, be rotatably coupled to a generator shaft34of the generator24through a gearbox36. As is generally understood, the rotor shaft32may provide a low speed, high torque input to the gearbox36in response to rotation of the rotor blades22and the hub20. The gearbox36may then be configured to convert the low speed, high torque input to a high speed, low torque output to drive the generator shaft34and, thus, the generator24.

Additionally, the turbine controller26may also be located within the nacelle16. As is generally understood, the turbine controller26may be communicatively coupled to any number of the components of the wind turbine10in order to control the operation of such components. For example, as indicated above, the turbine controller26may be communicatively coupled to each pitch adjustment mechanism30of the wind turbine10(one of which is shown) to facilitate rotation of each rotor blade22about its pitch axis28.

In general, each pitch adjustment mechanism30may include any suitable components and may have any suitable configuration that allows the pitch adjustment mechanism30to function as described herein. For example, in several embodiments, each pitch adjustment mechanism30may include a pitch drive motor38(e.g., any suitable electric motor), a pitch drive gearbox40, and a pitch drive pinion42. In such embodiments, the pitch drive motor38may be coupled to the pitch drive gearbox40so that the pitch drive motor38imparts mechanical force to the pitch drive gearbox40. Similarly, the pitch drive gearbox40may be coupled to the pitch drive pinion42for rotation therewith. The pitch drive pinion42may, in turn, be in rotational engagement with a pitch bearing44coupled between the hub20and a corresponding rotor blade22such that rotation of the pitch drive pinion42causes rotation of the pitch bearing44. Thus, in such embodiments, rotation of the pitch drive motor38drives the pitch drive gearbox40and the pitch drive pinion42, thereby rotating the pitch bearing44and the rotor blade22about the pitch axis28. In alternative embodiments, it should be appreciated that each pitch adjustment mechanism30may have any other suitable configuration that facilitates rotation of a rotor blade22about its pitch axis28.

During operation of the wind turbine10, the drivetrain assembly (i.e. the generator24, the gearbox36, and the corresponding shafts32,34) cause vibrations that are generated as sound throughout the nacelle16and the tower12, particularly the upper portion of the tower12. Such vibrations contribute significantly to an audible tonality in the vicinity of the turbine10. More specifically, the drivetrain assembly may cause tower surface vibrations that generate noise that can be a nuisance to neighbors of the wind turbine10. Thus,FIG. 3and illustrate schematic diagrams of various embodiments of a system100for reducing audible tonality near a wind turbine (e.g. the tower12of wind turbine10) that addresses the aforementioned issues.

As shown in the illustrated embodiments, the system100includes a plurality of damping elements102mounted on an inner surface104of the tower12of the wind turbine10. More specifically, in certain embodiments, the plurality of damping elements102may be mounted on an upper section106of the inner surface104of the tower12, however, it should be understood that the damping elements102may also be mounted at any other suitable location within the tower12. Further, the damping elements102may be mounted at a plurality of locations on the inner surface104of the tower12, where vibration levels are above a predetermined threshold.

For example, in certain embodiments, the damping elements102may be mounted at critical tower areas as determined by measuring vibrations or through modeling, e.g. Finite Element Method (FEM)/Boundary Element Method (BEM) simulation or similar. More specifically, as shown inFIG. 4, the damping elements102may be located within a vibration area128having vibration levels above the predetermined threshold. For example, as shown, a vibration typically has a shape having vibration nodes (i.e. where the vibration amplitude is zero) and vibration antinodes (i.e. where the vibration amplitude is maximal). As such, the damping elements102can be mounted at or near the antinode location(s). In certain embodiments, there may not be unique antinode locations, i.e. because a location that is in the antinode of one vibration type at one frequency may be not the antinode location for another vibration type at another frequency. Thus, by mounting the damping elements102across critical areas of the tower, at least a portion of the damping elements102will always be outside the nodes of the various vibration types.

In further embodiments, single point critical areas of the tower12having the strongest vibration antinodes/highest vibration amplitudes may be determined (using simulations and/or measurements) and the damping elements102can be located at such points. As such, the present disclosure provides a system and method for damping vibrations where distinct vibration types with distinct antinodes can be determined as well as in cases where distinct antinode areas cannot be determined (i.e. due to multiple vibration types).

Further, the upper section106of the tower12generally refers to the upper portion of the tower12closest to the nacelle16and therefore the portion typically most impacted by the drivetrain-induced vibrations. Thus, in certain embodiments, the upper section106of the tower12generally encompasses from about 15% to about 40% of an overall height of the tower12as measured from the top15of the tower12. Accordingly, during operation of the wind turbine10, the plurality of damping elements102are configured to damp vibrations of the upper section106of tower12so as to reduce audible tonality near the wind turbine10.

Referring now toFIGS. 5 and 6, the damping elements102may be tuned-mass dampers. As used herein, a tuned-mass damper generally refers to a damping device mounted to structures to reduce the amplitude of mechanical vibrations. Thus, tuned mass dampers are configured to stabilize against violent motion caused by harmonic vibration. More specifically, as shown in the illustrated embodiment, each of the damping elements102may include a cylindrical mass element108configured or mounted with a cylindrical elastomeric element110. In certain embodiments, the mass element108is selected such that its modal mass is less than from about 1% to about 5% of the modal mass of the tower12, more preferably less than about 2% of the modal mass of the tower12. In particular embodiments, 2% of the modal mass of the tower12corresponds to the total number of damping elements102, e.g. about 1000, with each element weighing from about one (1) to about two (2) kilograms. Further, the mass element108may be constructed of any suitable material, including but not limited to a metal (e.g. steel) or a metal alloy.

In addition, the elastomeric element110may be constructed of any suitable elastomer material, including but not limited to rubber, silicone, or similar. Thus, the elastomeric element110is generally designed in terms of stiffness and damping constants. As such, the modal mass of the mass element108and the stiffness of the elastomeric element110may set the target frequency of the damping element102. In certain embodiments, the damping ratio of the damping elements102is targeted to be from about 1% to about 25%. Thus, in certain embodiments, the plurality of damping elements102may have a frequency range of from about 80 Hertz (Hz) to about 800 Hz, which corresponds to the audible frequency range of typical steel towers, although it should be understood that any suitable frequency range may be selected so as to cover large parts of the wind turbine variable speed operation as well as multiple types of towers. More specifically, the tower12may have a specific type of vibration/vibration shape, which is critical with regard to tonality, although typical towers can have multiple critical vibration shapes at different frequencies. Thus, the damping elements102of the present disclosure can be tuned to a specific frequency, with its effectiveness broad enough to cover and counteract multiple vibration types at different frequencies.

It should be understood that any number of damping elements102may be utilized in the system100. For example, from one (1) to more than five hundred (500) damping elements102may be utilized in the system100. In additional embodiments, more than five hundred (500) damping elements102may be utilized in the system100. With the size of the damping elements102, the overall system100still minimizes additional weight added to the turbine10during operation. For example, for embodiments described herein, the system100adds less than 1.5 tons to the overall mass of the wind turbine10.

In additional embodiments, the damping elements102may be mounted on the inner surface104of the tower12via at least one of a magnet112, one or more fasteners (e.g. screws, bolts, etc.), and/or an adhesive (e.g. glue, tape, or similar). In additional embodiments, the magnet112may include any suitable magnet, including e.g. a neodymium standard element. In embodiments that utilize magnets, as shown inFIG. 5, the components of the damping element102, i.e. the mass element108, the elastomeric element110, and the magnet112, may be secured together via one or more fasteners114or screws configured through a central longitudinal axis116. For example, in one embodiment as shown inFIG. 7, the elastomeric element110may have a metal plate122configured at the tower-facing end thereof that contains a threaded hole124. As such, the magnet112may have a corresponding fastener head126configured to fit within the threaded hole124so as to secure the components together.

Referring toFIGS. 3 and 8, the damping elements102may be spaced in any suitable pattern on the inner surface104of the tower12. For example, as shown inFIG. 3, the damping elements102are spaced evenly apart in both the circumferential (or horizontal) direction118and the vertical direction120. Further, as shown inFIG. 8, spacing of the damping elements102in the vertical direction120may be determined as a function of vibration levels on the inner surface104of the tower12. Thus, as shown, the damping elements102may be evenly or randomly spaced in the vertical direction120. Alternatively, the plurality of damping elements102may be randomly spaced in both the horizontal and vertical directions118,120on the inner surface104of the tower12. In addition, as shown, the damping elements102may be arranged together in groups. After placement of the damping elements102, computer simulation and/or sensor measurements may be run once again on the tower12to determine the effectiveness of the damping elements102.

Referring now toFIG. 9, a flow diagram of one embodiment of a method200for reducing audible tonality generated by a drivetrain assembly of a wind turbine10is illustrated. As shown at202, the method200includes determining one or more locations on an inner surface104of the tower12of the wind turbine10having vibration levels above a predetermined threshold, e.g. above a critical level that causes undesirable noise levels to neighboring properties of the wind turbine10. As shown at204, the method200includes mounting a damping element102at each of the locations on the inner surface104of the tower12of the wind turbine10having a high vibration level. Thus, during operation of the wind turbine10, the damping elements102are configured to damp vibrations of the tower12so as to reduce audible tonality generated by the drivetrain assembly.

In one embodiment, the step of determining one or more locations on the inner surface104of the tower12of the wind turbine10having vibration levels above a predetermined threshold may include measuring vibration levels at the one or more locations or determining, via computer simulation, the location(s) as a function of at least one of the tower size/shape of the tower12and/or location of the tower12. More specifically, the locations may be determined using FEM/BEM simulation.

In another embodiment, the method200may include selecting the modal mass of the mass element and the stiffness of the elastomeric element so as to set a target frequency of the damping element102.

Further, the method200may include omitting damping elements102in locations containing flanges. In additional embodiments, the method200may include spacing the plurality of damping elements102evenly apart in the circumferential direction118. Moreover, the method200may include spacing the plurality of damping elements102in a vertical direction120as a function of vibration levels on the inner surface104of the tower12, e.g. via simulation.

In alternative embodiments, the method200may include spacing the damping elements102randomly on the inner surface104of the tower12.

Referring now toFIG. 10, a flow diagram of one embodiment of a method300for reducing audible tonality generated by a drivetrain assembly of a wind turbine10is illustrated. As shown at302, the method300includes determining a vibration area128on a tower12of the wind turbine10having vibration levels above a predetermined threshold. As shown at304, the method300also includes mounting a plurality of damping elements102within the vibration area102of the tower of the wind turbine at or near antinode locations. Thus, during operation of the wind turbine10, the damping elements102are configured to damp vibrations of the tower12so as to reduce audible tonality generated thereby.