Ultrasonic sound emitting devices for wind turbines

A rotor blade for a wind turbine is disclosed. The rotor blade may generally include a body extending between a blade root and a blade tip. The body may include a pressure side and a suction side extending between a leading edge and a trailing edge. In addition, the rotor blade may include a nozzle mounted on or within the body. The nozzle may include an inlet, an outlet and a converging section between the inlet and the outlet. The converging section may be configured to accelerate a flow of air through the nozzle such that an ultrasonic sound emission is produced.

FIELD OF THE INVENTION

The present subject matter relates generally to wind turbines and, more particularly, to ultrasonic sound emitting devices that may be mounted on or within wind turbine rotor blades to deter bats.

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. However, while being considered environmentally safe, wind turbines can pose a threat to bats. Specifically, it has been found that bats may have trouble detecting the rotating rotor blades of a wind turbine. As a result, bats can be struck by the rotor blades and killed. The occurrence of such bat strikes have led many to enact regulations and/or laws prohibiting and/or discouraging the placement of wind turbines in areas of high bat populations and/or restricting the operations of the wind turbines at night.

Many believe that ultrasonic sound in the frequency range of about 25 kHz to about 100 kHz may be effective at deterring bats by interfering with both the bats' natural sonar and their ability to hunt insects. However, generating enough sound to cover the entire rotor diameter of a wind turbine has proved to be a difficult task. For example, previous attempts have focused on the use of speakers mounted on the nacelle. Unfortunately, due to dissipation of the sound, it has been found that nacelle mounted speakers are incapable of generating enough acoustic power to cover the entire rotor diameter of the wind turbine.

Accordingly, a blade mounted, ultrasonic sound emitting device that is capable of producing sufficient acoustic power to cover the entire rotor diameter of a wind turbine would be welcomed in the technology.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, the present subject matter is directed to a rotor blade for a wind turbine. The rotor blade may generally include a body extending between a blade root and a blade tip. The body may include a pressure side and a suction side extending between a leading edge and a trailing edge. In addition, the rotor blade may include a nozzle mounted on or within the body. The nozzle may include an inlet, an outlet and a converging section between the inlet and the outlet. The converging section may be configured to accelerate a flow of air through the nozzle such that an ultrasonic sound emission is produced.

In another aspect, the present subject matter directed to a wind turbine including a tower, a nacelle mounted atop the tower and a rotor coupled to the nacelle. The rotor may include a hub and at least one rotor blade extending outwardly from the hub. Additionally, the wind turbine may include a nozzle mounted on or within the rotor blade. The nozzle may include an inlet, an outlet and a converging section between the inlet and the outlet. The converging section being configured to accelerate a flow of air through the nozzle such that an ultrasonic sound emission is produced.

In a further aspect, the present subject matter is directed to a method for producing an ultrasonic sound emission from a rotor blade of a wind turbine. The method may generally include rotating the rotor blade such that an airflow is directed through a nozzle mounted to an exterior surface of the rotor blade, the nozzle including an inlet, an outlet and a converging section between the inlet and outlet and accelerating the airflow through the converging section such that an ultrasonic sound emission is produced.

DETAILED DESCRIPTION OF THE INVENTION

In general, the present subject matter is directed to rotor blades having ultrasonic sound emitting devices configured to produce sound at a frequency within the ultrasonic range (e.g., from about 25 kHz to about 100 kHz). In several embodiments, the ultrasonic sound emitting devices may be passive devices. For example, in one embodiment, a converging nozzle may be mounted to the exterior of a rotor blade such that, as the rotor blade rotates, an airflow is directed into the nozzle and is choked, thereby producing an air jet (e.g., a supersonic jet) at the nozzle outlet that emits sound within the ultrasonic frequency range. In other embodiments, the ultrasonic sound emitting devices may be active devices. For instance, a converging nozzle may be mounted within the body of a rotor blade such that the nozzle outlet extends through the body and is exposed to the exterior of the blade. In such an embodiment, an airflow from a pressurized air source may be directed into the nozzle to produce an air jet at the nozzle outlet that emits sound within the ultrasonic frequency range. Regardless, it is believed that the ultrasonic sound emitting from the disclosed nozzles may deter bats from flying into and/or adjacent to a wind turbine. Additionally, due to the fact that the disclosed nozzles may be mounted on or within the rotor blades of a wind turbine, the ultrasonic sound emission produced by the nozzles may cover the entire rotor diameter of the wind turbine.

Referring now toFIG. 2, a perspective view of one of the rotor blades22shown inFIG. 1is illustrated. As shown, the rotor blade22generally includes a blade root24and a blade tip26disposed opposite the blade root24. A body28of the rotor blade22extends lengthwise along a longitudinal axis30between the blade root24and the blade tip26and generally serves as the outer shell of the rotor blade22. As is generally understood, the blade body28may define an aerodynamic profile to enable the rotor blade22to capture kinetic energy from the wind using known aerodynamic principles. Thus, the body28may generally include a pressure side32and a suction side34extending between a leading edge36and a trailing edge38. Additionally, the rotor blade22may have a span40defining the total length of the body28between the blade root24and the blade tip26and a chord42defining the total length of the body28between the leading edge36and the trailing edge38. As is generally understood, the chord42may vary in length with respect to the span40as the rotor blade22extends from the blade root24to the blade tip26.

As indicated above, the body28of the rotor blade22may generally define an aerodynamic profile or shape. For example, in several embodiments, the body28may define an airfoil shaped cross-section, such as by defining a symmetrical or cambered airfoil-shaped cross-section. In addition, the rotor blade22may also be aeroelastically tailored. Aeroelastic tailoring of the rotor blade22may entail bending of the blade22in a generally chordwise direction and/or in a generally spanwise direction. The chordwise direction generally corresponds to a direction parallel to the chord42of the rotor blade22. The spanwise direction generally corresponds to a direction parallel to the span40or longitudinal axis30of the rotor blade22. Aeroelastic tailoring may further entail twisting of the rotor blade22, such as twisting the blade22in a generally chordwise and/or spanwise direction.

Referring now toFIGS. 3 and 4, there is illustrated one embodiment of a passive, ultrasonic sound emitting device100that may be mounted onto the exterior of a rotor blade22. In particular,FIG. 3illustrates a partial, perspective view of a rotor blade22having the ultrasonic sound emitting device100mounted thereon. Additionally,FIG. 4illustrates a cross-sectional view of the ultrasonic sound emitting device100shown inFIG. 3taken about line4-4.

As shown, in several embodiments, the ultrasonic sound emitting device100may comprise a converging nozzle100configured to generate an air jet (e.g., a supersonic jet) as air flows through the nozzle100. For example, as particularly shown in the illustrated embodiment, the nozzle100may be mounted to an exterior surface102of the body28of a rotor blade22. Thus, as the rotor blade22rotates during operation of the wind turbine10, air flowing over the surface of the rotor blade may be directed into and accelerated through the nozzle100. By appropriately selecting the dimensions of the nozzle100, the airflow through the nozzle100may be accelerated to the point of choking (i.e., at or above a speed of Mach 1), thereby producing a supersonic jet. As the air jet104exits the nozzle100, a shock wave-expansion system (i.e., shock cells or a shock cell structure/pattern) is created such that, as the turbulence in the shear layers around the jet104interact with the shock cells, an ultrasonic sound emission may be generated within a frequency ranging from about 25 kHz to about 100 kHz.

As particularly shown inFIG. 4, the nozzle100may generally include an inlet106, an outlet108and a converging section110extending between the inlet106and the outlet108. In general, it should be appreciated that the size and shape of the inlet106may be selected so that a sufficient amount of air is captured by the nozzle100in order to generate an air jet104at the nozzle outlet108capable of producing an ultrasonic sound emission. For example, in several embodiments, the inlet106may have a circular shape (e.g., by defining a bellmouth inlet) with a diameter112. In other embodiments, the inlet106may have a non-circular shape, such as a rectangular shape (e.g., by defining a scoop inlet). Regardless, in several embodiments, a ratio of the cross-sectional area of inlet106to the cross-sectional area of the outlet108may range from about 3:1 to about 100:1, such as from about 3:1 to about 15:1 or from about 30:1 to about 100:1 or from about 15:1 to about 30:1 and all other subranges therebetween. However, it is foreseeable by the inventors of the present subject matter that the ratio of the cross-sectional area of inlet106to the cross-sectional area of the outlet108may be smaller and/or larger than the values contained within the ranges described above.

The converging section110may generally correspond to a portion of the nozzle100along which the cross-sectional area of the nozzle100steadily decreases between the inlet106and the outlet108, thereby causing the air entering the inlet106to be accelerated as its flows through the converging section110. Thus, by appropriately selecting the size of the outlet108, the airflow through the converging section110may be choked as it reaches the outlet108. As is generally understood, the cross-sectional area required to choke the airflow may generally vary depending on the total mass flow through the nozzle100(which may relate to the size of the inlet106) and the total pressure of the flow (which may relate to the operating conditions of the wind turbine10as the rotor blades22rotate). However, in several embodiments, the outlet108may have a diameter114ranging from about 1 millimeter (mm) to about 15 mm, such as from about 1 mm to about 5 mm or from about 5 mm to about 15 mm and all other subranges therebetween. However, it is foreseeable by the inventors of the present subject matter that the diameter114of the outlet108may be smaller and/or larger than then values contained within the ranges described above.

It should be appreciated that, in several embodiments, the diameter114of the outlet108may be selected so as to specifically tailor the frequency of the ultrasonic sound emission produced by the nozzle100. For instance, in one embodiment, an outlet diameter114ranging from about 5 mm to about 15 mm may be utilized to produce ultrasonic sound at a frequency of about 25 kHz while an outlet diameter114ranging from about 1 mm to about 5 mm may be utilized to produce ultrasonic sound at a frequency of about 100 kHz. Accordingly, it may be desirable to position multiple nozzles100having different outlet diameters114on each rotor blade22such that ultrasonic sound emissions at different frequencies may be produced.

It should be appreciated that the nozzle100may generally be configured to be mounted at any suitable location along the exterior surface102of the blade body28(e.g., at any suitable location along the pressure side32or suction side34of the rotor blade22). For example, as shown inFIG. 3, in one embodiment, the nozzle100may be mounted to the exterior surface102of the blade body28at or adjacent to the blade tip26. In alternative embodiments, the nozzle100may be mounted at any other suitable location along the span40of the rotor blade22, such as by mounting the nozzle100around the middle of the span40or at location proximal to the blade root24. Similarly, the nozzle100may be mounted at any suitable location along the chord42of the rotor blade22. For example, as shown inFIG. 3, the nozzle100may be mounted to the rotor blade22such that the inlet106is located at or adjacent to the leading edge36. However, in other embodiments, the nozzle100may be mounted at a location closer to the trailing edge38.

It should also be appreciated that, in several embodiments, a plurality of nozzles100may be mounted to the exterior surface102of the blade body28. For example, in one embodiment, a plurality of nozzles100may be grouped together at a particular location on the rotor blade22. Alternatively, the nozzles100may be spaced apart along the exterior surface102of the rotor blade22, such as by being spaced apart along the span40and/or chord42on the pressure and/or suction side32,34of the blade22.

Additionally, it should be appreciated that, in several embodiments, the location and number of nozzles100on each rotor blade22may be selected such that a specific noise level output is achieved a predetermined distance from the wind turbine (e.g., at a distance that is sufficient to allow bats to avoid being struck by the rotor blades). For instance, in one embodiment, the location and number of nozzles100on each rotor blade22may be selected such that the noise level at a predetermined distance from the wind turbine is greater than 65 decibels (dBs), such as greater than 70 dBs or greater than 75 dBs.

Moreover, it should be appreciated that each nozzle100may generally be mounted to the exterior surface102of the blade body28using any suitable fastening means and/or method known in the art. For example, in one embodiment, each nozzle100may be mounted to the blade body28using one or more suitable fastening mechanisms (e.g., screws, bolts, pins, rivets, brackets and/or the like). Alternatively, each nozzle100may be mounted to the blade body28using a suitable tape or adhesive material.

Referring now toFIG. 5, a cross-sectional view of another embodiment of the nozzle100shown inFIGS. 3 and 4is illustrated in accordance with aspects of the present subject matter. As shown, the nozzle100may be configured as a de Laval or any other suitable convergent-divergent nozzle. Thus, in addition to having an inlet206, an outlet208and a converging section210, the nozzle100may also include a diverging section216extending between the converging section210and the outlet208. In such an embodiment, a nozzle throat218may be located between the converging section210and the diverging section216and may define the point at which the cross-sectional area of the nozzle100transitions from decreasing (along the converging section210) to increasing (along the diverging section216).

By configuring the nozzle100in the manner shown inFIG. 5, the airflow may, for example, be accelerated to a supersonic speed as it flows through the converging section210and into the nozzle throat218. Thus, similar to the outlet108described above, the size of the nozzle throat218may generally be selected based on the total mass flow through the nozzle100(which may relate to the size of the inlet206) and the total pressure of the flow (which may relate to the operating conditions of the wind turbine10as the rotor blades22rotate). For example, in embodiments in which the inlet206is sized similar the inlet206described above, the nozzle throat218may have a diameter220ranging from about 1 millimeter (mm) to about 15 mm, such as from about 1 mm to about 5 mm or from about 5 mm to about 15 mm and all other subranges therebetween. However, it is foreseeable by the inventors of the present subject matter that the diameter220and/or cross-sectional area of the nozzle throat218may be smaller and/or larger than then values contained within the ranges described above.

In addition, by configuring the nozzle100to include the diverging section216, the air jet104traveling through the nozzle throat218may expand as it flows through the diverging section216. Such expansion may generally allow the shape of air jet104to be modified as it exits through the outlet208, thereby altering the frequency of the ultrasonic sound emitted by the jet208. It should be appreciated that the diameter/cross-sectional area to which the nozzle100increases between the throat218and the outlet208may generally vary depending on the sound characteristics desired to be achieved, the dimensions of the inlet206and nozzle throat218and/or various other parameters/conditions. However, in several embodiments, a ratio of the cross-sectional area of the outlet108to the cross-sectional area of the throat218may range from about 1:1 to about 1.2:1, such as from about 1.03:1 to about 1.1:1 or from about 1.1:1 to about 1.2:1 and all other subranges therebetween. However, it is foreseeable by inventors of the present subject matter that the ratio of the cross-sectional area of the outlet108to the cross-sectional area of the throat218may be smaller and/or larger than then values contained within the ranges described above.

It should be appreciated that, in addition to being mounted on an exterior surface102of the body28of a rotor blade22, the nozzles100described above may also be mounted within the blade body28. For example,FIG. 6illustrates the nozzle100shown inFIGS. 3 and 4mounted partially within the body28. Specifically, as shown, the nozzle100is mounted within the rotor blade22such that the outlet108extends through the blade body28to an exterior surface102of the blade22. As such, the air jet104generated within the nozzle100may be expelled to the exterior of the rotor blade22, thereby ensuring that the ultrasonic sound emission generated as the jet104exits the nozzle100propagates outwardly from the rotor blade22.

To supply air to the nozzle100in such embodiment, the inlet106may be in flow communication with a pressurized air source (e.g., an air compressor, pressurized vessel and/or the like). For example, as shown inFIG. 6, the pressurized air source140may be disposed within the rotor blade22and may be in flow communication with the nozzle100inlet via a hose142or other suitable coupling. Alternatively, the pressurized air source140may be disposed at any other suitable location (e.g., within the hub20, nacelle116or tower12of a wind turbine10) and may be coupled to the nozzle inlet106via any suitable fluid coupling.

It should be appreciated that the pressurized air source140may generally be configured to supply air to the nozzle100at any given pressure. As such, the diameters112,114(FIG. 4) or cross-sectional areas of the inlet106and outlet108(and, in some instances, the diameter/cross-sectional area of the nozzle throat218(FIG. 5)) may generally be selected such that, at the given air pressure, an air jet104is expelled from the nozzle outlet108that is capable of producing an ultrasonic sound emission.

It should also be appreciated that the nozzle100may be mounted within the rotor blade22such that the outlet108extends through the blade body28at any suitable location along the blade22. For example, as shown inFIG. 6, the nozzle100is positioned within the rotor blade22such that the outlet108extends through the blade body28at the trailing edge38. However, in other embodiments, the outlet108may be configured to extend through the blade body28at the leading edge36or at any position on the pressure side34or the suction side36of the rotor blade22. Additionally, in several embodiments, a plurality of nozzles100mounted within the rotor blade22. For example, in one embodiment, a plurality of nozzles100may be mounted within the rotor blade22such that the outlet108of each nozzle100extends through the blade body28at the trailing edge38at various locations along the span40of the blade22.

Referring now toFIG. 7, a cross-sectional view of another embodiment of an ultrasonic sound emitting device300that may be mounted to an exterior surface102of the body28of a rotor blade22is illustrated in accordance with aspects of the present subject matter. As shown, the ultrasonic sound emitting device300may be configured as a Hartmann generator or any other suitable powered resonance tube. Thus, the device300may include both a converging nozzle302and a closed-end tube304disposed downstream of the nozzle302.

In general, the nozzle302may be configured the same as or similar to the nozzle100described above with reference toFIGS. 3 and 4. For example, as shown inFIG. 7, the nozzle302may include an inlet306, an outlet308and a converging section310extending between the inlet306and the outlet308. As described above, the nozzle302may generally be configured to generate an air jet312(e.g., a supersonic jet) as air flows through the nozzle302. Thus, the dimensions of the inlet306and the outlet308may generally be selected so that a sufficient amount of air is captured and accelerated through the nozzle302in order to produce such a jet312. For instance, in one embodiment, the diameters or cross-sectional areas of the inlet306and outlet308may be the same as or similar to the diameters or cross-sectional areas of the inlet106and outlet108described above.

Similar to various Hartmann generators and/or other powered resonance tubes known in the art, the closed-end tube304may generally be configured to have the same diameter and/or cross-sectional area as the nozzle outlet308and may be aligned with the outlet308such that the air jet312exiting the nozzle302is directed into the tube304. Thus, by positioning the tube304relative to the outlet308so that the tube304is disposed within a compression region314of the shock cell structure/pattern created at the outlet308as the jet312exits the nozzle302, a strong flow instability (including successive compression and expansion waves) may be created within the tube304. As a result of such flow instability, an ultrasonic sound emission may be generated by the ultrasonic sound emitting device300at a frequency ranging from about 25 kHz to about 100 kHz.

It should be appreciated that the closed-end tube304may generally be mounted in alignment with the nozzle outlet308using any suitable means and/or method known in the art. For example, as shown inFIG. 7, the tube304may be mounted to the rotor blade22using any suitable coupling316(e.g., a pin, bolt, rod and/or other suitable linkage) that permits the tube304to be positioned in alignment with the nozzle outlet308. Alternatively, the tube304may be held in alignment with the nozzle outlet308via a coupling or linkage extending between the tube304and the nozzle302.

Referring now toFIG. 8, the ultrasonic sound emitting device300shown inFIG. 7is illustrated in a configuration in which the nozzle302is partially mounted within the rotor blade22. Specifically, as shown, the nozzle302is mounted within the rotor blade22such that the outlet308extends through the blade body38. As such, the air jet312generated within the nozzle302may be expelled to the exterior of the rotor blade22. Additionally, as shown, the closed-end tube304may be mounted outside the rotor blade22(e.g., using a suitable coupling316) such that the tube304is generally aligned with the nozzle outlet308. As such, the air jet312generated by the nozzle302may be directed into the closed-end tube304, thereby producing an ultrasonic sound emission propagating outwardly from the rotor blade22.

As shown inFIG. 8, similar to the embodiment described above with reference toFIG. 6, the nozzle inlet306may be in flow communication with a suitable pressurized air source140(e.g., an air compressor, pressurized vessel and/or the like) via a hose142or other suitable coupling. In such an embodiment, the pressurized air source140may generally be configured to supply air to the nozzle302at any given pressure. Thus, the diameters or cross-sectional areas of the inlet306and outlet308may generally be selected such that, at the given air pressure, an air jet312is expelled from the nozzle outlet308and into the closed-end tube304that allow an ultrasonic sound emission to be produced.

Additionally, it should be appreciated that the nozzle302may be mounted within the rotor blade22such that the outlet308extends through the blade body28at any suitable location along the blade22. For example, as shown inFIG. 8, the nozzle302is positioned within the rotor blade22such that the outlet308extends through the blade body28at the trailing edge38. In other embodiments, the outlet308may be configured to extend through the blade body28at the leading edge36or at any position on the pressure side34or the suction side36of the rotor blade22. However, regardless of the positioning of the nozzle302, the closed-end tube304may be configured to be mounted relative to the nozzle302such that the tube304is aligned with the nozzle outlet308.

It should be appreciated that the present subject matter is also directed to a method for producing an ultrasonic sound emission from a rotor blade22of a wind turbine10. In several embodiments, the method may include rotating the rotor blade100such that an air flow is directed through a nozzle100,302mounted to an exterior surface102of the rotor blade22, the nozzle100,302including an inlet106,206,306, an outlet108,208,308and a converging section110,210,310between the inlet106,206,306and outlet108,208,308and accelerating the air flow through the converging section110,210,310such that an ultrasonic sound emission is produced.

It should also be appreciated that, although the present subject matter has been described herein as using converging nozzles to produce ultrasonic sound emissions, various other ultrasonic sound emitting devices may also be used to deter bats from a wind turbine. For example, in one embodiment, a speaker capable of producing ultrasonic sound emissions may be mounted on or within a rotor blade22. Alternatively, various other devices, such as a powered Helmholtz resonator, a dual bi-morph synthetic jet and/or the like, may be mounted on or within a rotor blade22in order to produce ultrasonic sound emissions.

Additionally, although the present subject matter has been described primarily as using converging nozzles to produce a supersonic air jet, ultrasonic sound emissions may also be produced with sub-sonic air jets. Thus, it should be appreciated that the disclosed subject matter may generally be utilized to generate any suitable air jet that is capable of producing an ultrasonic sound emission.