SENSOR DEVICE FOR AN AERODYNAMIC ELEMENT

Abstract

A sensor device for measuring flow-separation on an aerodynamic element, including a number of compliant elements with aerodynamic and/or structural properties designed to allow flow-induced vibrational motion in an air current and a sensor-element designed to measure vibrations of the number of compliant elements is provided. Further provided is an aerodynamic element, e.g. a wind turbine blade or an airfoil, with such sensor device, a method for controlling the angle of attack of an aerodynamic element, a controlling device and a wind turbine.

Claims

1. A sensor device for detecting flow-separation on an aerodynamic element, comprising: a plurality of compliant elements with aerodynamic and/or structural properties designed to allow flow-induced vibrational motion in an air current downstream of a trailing edge of an aerodynamic element; and a sensor-element designed to measure vibrations of the plurality of compliant elements.

2. The sensor device according to claim 1, wherein a compliant element of the plurality of compliant elements has an elongated shape with a ratio of length to width greater than 3 to 1, and is designed to be attached perpendicular to the trailing edge of the aerodynamic element.

3. The sensor device according to claim 2, wherein a compliant element has a minimum length of 1 cm, and/or a maximum length of 20 cm, and/or a minimum width of 1 mm, and/or a maximum width of 40 mm.

4. The sensor device according to claim 1, comprising more than two compliant elements protruding from a common root-element , wherein the compliant elements are arranged parallel to each other having a minimum spacing to an adjacent compliant element of 1 mm, and/or a maximum spacing to an adjacent compliant element of 10 mm.

5. The sensor device according to claim 1, wherein the plurality of compliant elements are designed as filaments of a comb-structure or as teeth of a serration, or as filaments of a combed serration or a combed trailing edge treatment device of an airfoil or a wind turbine blade.

6. The sensor device according to claim 1, wherein the sensor-element comprise a sensor for optical measurements, or a strain gauge-sensor connected with a compliant element or a compliant element formed as strain gauge element, or an accelerometer that is mounted on the compliant element, measuring an acceleration of the compliant element, or an acoustic sensor measuring sound waves in the aerodynamic element.

7. The sensor device according to claim 1, comprising a comparator unit designed to determine if the vibration of a compliant element, preferably the amplitude or energy of the vibration, a lift coefficient or a strain gauge signal, an acceleration signal or an acoustic signal of the sensor-element, exceeds a predefined threshold.

8. The sensor device according to claim 1, comprising a signal-unit designed to create a control signal based on a vibration of a compliant element, wherein the control signal is designed to bias a control unit of a wind turbine to adjust a pitch angle and/or a rotation speed of the aerodynamic element according to the control signal.

9. An aerodynamic element, comprising a sensor device according to claim 1 located downstream of the trailing edge of the aerodynamic element.

10. A method for controlling an angle of attack of the aerodynamic element according to claim 9, comprising the steps: measuring a vibration of a compliant element of a sensor device of the aerodynamic element, and adjusting a pitch angle and/or a rotation speed of the aerodynamic element based on a measurement of the vibration.

11. The method according to claim 10, comprising the steps: a) measuring a strength of the vibration of a compliant element at different times at a first pitch angle of the aerodynamic element, b) comparing the measurement of step a) with a predefined threshold-value, c) changing the pitch angle of the aerodynamic element from the first pitch angle to a second pitch angle, if the measurement exceeds the predefined threshold-value, d) measuring the strength of the vibration of a compliant element at the second pitch angle of the aerodynamic element, and e) repeating the steps b) to d) until the measurement of the strength of the vibration at the second pitch angle lies below the predefined threshold-value, wherein the second pitch angle differs less than 5 from the first pitch angle.

12. The method according to claim 11, wherein the threshold-value is determined with calibration measurements, while measuring the vibrations with different pitch angles and/or different rotation speeds and/or during different wind velocities.

13. The method according to claim 10, comprising the steps: measuring the vibration of a compliant element of a sensor device of the aerodynamic element at different pitch angles of the aerodynamic element, and adjusting the pitch angle of the aerodynamic element in a direction of the pitch angle where weaker vibrations have been measured in the case where the measurement exceeds a predefined threshold value.

14. A controlling device for adjusting an angle of attack of an airstream on an aerodynamic element according to claim 9, comprising: means to measure the vibration of a compliant element of a sensor device of the aerodynamic element, a sensor-element measuring the strength of the vibration of the compliant element and a comparator unit designed to determine, if the strength of the vibration exceeds a predefined threshold value, and a control unit designed to adjust the pitch angle and/or the rotation speed of the aerodynamic element based on the measurement of the vibration, and a signal-unit to bias the adjustment.

15. A wind turbine comprising an aerodynamic element according to claim 9 and a controlling device.

Description

BRIEF DESCRIPTION

[0059] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0060] FIG. 1 shows a cross section of an embodiment of an aerodynamic element;

[0061] FIG. 2 shows a top view on an embodiment of a sensor device;

[0062] FIG. 3 shows a top view on a further embodiments of a sensor device;

[0063] FIG. 4 shows exemplary measurements of a sensor element;

[0064] FIG. 5 shows a block diagram of an embodiment of a method; and

[0065] FIG. 6 shows an embodiment of a wind turbine.

DETAILED DESCRIPTION

[0066] FIG. 1 shows a cross section of a preferred aerodynamic element 1, e.g. an airfoil or wind turbine blade, comprising a sensor device 2 according to embodiments of the invention. The sensor device 2 is located downstream of the trailing edge of the aerodynamic element 1.

[0067] An air current C is indicated flowing against the aerodynamic element 1 in a certain angle of attack AoA. Here a great angle of attack AoA is shown, where flow separation occurs at about the half of the upper surface of the aerodynamic element 1 forming a separation zone SZ where flow separation occurs. This is indicated with eddies at the trailing edge la of the aerodynamic element 1.

[0068] FIG. 2 shows a top view on a preferred sensor device 2 positioned at the trailing edge 1a of an aerodynamic element 1. The sensor device 2 comprises a compliant element 3 having an elongated shape attached perpendicular to the trailing edge 1a of the aerodynamic element 1. This compliant element 3 is able to vibrate in an air current and will strongly vibrate if the air current is turbulent.

[0069] An accelerometer 4a as sensor-element 4a is mounted on the compliant element 3, measuring the acceleration of the compliant element 3 during vibration. Here, also a strain gauge sensor 4b (see FIG. 3) could be used that is included in the compliant element 3 so that the compliant element 3 itself can be used as a strain gauge element.

[0070] FIG. 3 shows a top view on a further preferred sensor device 2. The sensor device 2 comprising a vast number of compliant elements 3 protruding from a common root-element 3a. The compliant elements 3 are designed as filaments of a comb-structure of a combed serration.

[0071] The sensor device 2 comprises two different sensor-elements 4b, 4c, for example an optical sensor 4c for optical measurements (could also be an acoustic sensor) and a strain gauge sensor 4b.

[0072] The sensor device 2 comprises a comparator-unit 5 designed to determine if the vibration of a compliant element 3, exceeds a predefined threshold, and a signal-unit 6 designed to create a control signal based on the vibration of a compliant element 3. The sensor-elements 4b and 4c are providing their measured values to the comparator-unit 5 for comparison with a predefined threshold value T.

[0073] Looking at FIG. 6, the signal-unit 6 of this sensor device 2 (shown in FIG. 3) preferably communicates with the control unit 8 of a wind turbine 7, biasing this control unit 8 to adjust the pitch angle P of the aerodynamic element 1.

[0074] FIG. 4 shows two exemplary measurements of a sensor element at different angles of attack AoA. The upper diagram shows a measured lift coefficient C.sub.L of an aerodynamic element 1, the lower diagram shows the amplitude A of the vibration of a compliant element 3 (see e.g. FIG. 2 or 3). At an angle of attack AoA greater 10 flow separation FS occurs (shown with the left dash/dottet line). At an angle of attack AoA of about 11.5, stall S occurs (shown with the right dash/dottet line) i.e. as soon as lift starts to reduce with angle of attack. This can be seen by characteristic changes in the gradient of the upper diagram. For example, the Amplitude A will rise strongly at a steep gradient when flow separation FS occurs.

[0075] In the lower diagram, a predefined threshold value T is shown. If the amplitude A exceeds this threshold value, this is interpreted that flow separation FS occurs. In this example, flow separation FS has already occurred but loss of lift (i.e. stall) has not when the threshold value T is exceeded. This could be optimized by calibration measurements or by a combined comparison of different values, e.g. the absolute amplitude A and the gradient of the amplitude A.

[0076] FIG. 5 shows a block diagram of a preferred method for controlling the angle of attack AoA of an aerodynamic element 1.

[0077] In step I, the vibration of a compliant element 3 of a sensor device 2 of the aerodynamic element 1 with the respective sensor-element 4a, 4b, 4c (see e.g. FIG. 2 or 3). The strength of the vibration of a compliant element 3 is measured continuously at different times, since the direction and/or strength of the wind current may change anytime.

[0078] In step II, every measurement is compared with a predefined threshold-value T.

[0079] In step III it is decided, whether the threshold-value T is exceeded or not. Since the direction and/or strength of the wind current may change anytime, this decision should be repeated with every measurement. If the threshold-value T is not exceeded, the method continues with step I.

[0080] In step IV, the pitch angle P of the aerodynamic element 1 (now called first pitch angle P) is changed to a second pitch angle P, if the measurement exceeds the predefined threshold-value T.

[0081] After that, the method continues with step I, wherein the strength of the vibration of a compliant element at the second pitch angle P of the aerodynamic element 1 is measured.

[0082] It is preferred, that the change of the pitch angle is performed such that the second pitch angle P, where the threshold value T is not exceeded differs less than 5 from the first pitch angle P, where the threshold value T is exceeded.

[0083] The threshold-value T could be predefined as static value. However, it could be determined with calibration measurements, preferably while measuring the vibrations with different pitch angles P and/or preferably during different wind velocities.

[0084] FIG. 6 shows a preferred wind turbine 7 comprising three aerodynamic elements 1 (wind turbine blades) and a controlling device 9. The rotor of the wind turbine rotates in an air current in the direction of the straight arrow shown at the upper wind turbine blade.

[0085] An aerodynamic element 1 comprises a sensor device 2 according to embodiments of the invention. Although due to enhance clearness, only one reference sign is shown, it is preferred that every aerodynamic element 1 comprises a sensor device 2. The sensor devices 2 each comprise a number of compliant elements 3 and sensor-elements 4a, 4b, 4c and could e.g. be designed as shown in FIGS. 1 to 3.

[0086] The controlling device is formed by the sensor device(s) 2 and the control unit 8 of the turbine. The control unit 8 is able to adjust the pitch angle P (a change of the pitch angle P is shown by the curved arrow around the upper wind turbine blade).

[0087] In the case the sensor-element 4a, 4b, 4c of a sensor device 2 of an aerodynamic element 1, measures a strong increase of the vibration of the compliant element (3) of this sensor device, the pitch angle P of this aerodynamic element 1 is adjusted by the control unit 8.

[0088] In the diagrams, like numbers refer to like objects throughout. Objects in the diagrams are not necessarily drawn to scale.

[0089] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention. For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements. The mention of a unit or a device does not preclude the use of more than one unit or device.

[0090] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0091] For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements.