Wind turbine blade comprising a noise reducing device

1. A noise reducing device ( 19 ) for a wind turbine blade ( 5 ), having a first end ( 22 ), a second end ( 25 ), a first local side surface ( 27 ) and a second local side surface ( 29 ) arranged between the first end ( 22 ) and the second end, wherein the noise reducing device ( 19 ) is configured for attachment to a side surface of the wind turbine blade ( 5 ), the noise reducing device ( 19 ) comprising a plurality of airflow modifying elements ( 20 ), a plurality of noise reducing elements ( 23 ) and at least one base part ( 26 ), the airflow modifying elements ( 20 ) extending from a first proximal end ( 21 ) to the first end ( 22 ), the noise reducing elements ( 23 ) extending from an opposite facing second proximal end ( 24 ) to the second end ( 25 ), and the at least one base part ( 26 ) extending from the first proximal end ( 21 ) to the second proximal end ( 24 ), wherein the airflow modifying elements ( 20 ) and the noise reducing elements ( 23 ) extend in opposite longitudinal directions from the first end ( 22 ) to the second end ( 25 ), the second local side surface ( 29 ) of each of the airflow modifying elements ( 20 ) and the at least one base part ( 26 ) forming a continuous flat side surface and being configured to contact and/or to be directly attached to said side surface of the wind turbine blade ( 5 ), the noise reducing device ( 19 ) being further configured to be arranged relative to a trailing edge ( 10 ) of the wind turbine blade ( 5 ), the trailing edge ( 10 ) being a truncated trailing edge ( 10 ″), and wherein the noise reducing device ( 19 ) has a local edge surface ( 28 ) facing the first end ( 22 ).

2. The noise reducing device according to claim 1 , wherein at least the airflow modifying elements ( 20 ) or the noise reducing elements ( 23 ) are integrally formed with the at least one base part ( 26 ).

3. The noise reducing device according to claim 1 , wherein each of the airflow modifying elements ( 20 ) has a first length measured from the first proximal end ( 21 ) to the first end ( 22 ) and each of the noise reducing elements ( 23 ) has a second length measured from the second proximal end ( 24 ) to the second end ( 25 ), wherein the first length is equal to or less than the second length.

4. The noise reducing device according to claim 1 , wherein each of the airflow modifying elements ( 20 ) has a first width measured along the first proximal end ( 21 ) and each of the noise reducing elements ( 23 ) has a second width measured along the second proximal end ( 24 ), wherein the first width is equal to or less than the second width.

5. The noise reducing device according to claim 1 , wherein each of the airflow modifying elements ( 20 ) has a first profile and each of the noise reducing elements ( 23 ) has a second profile, wherein the first profile differs from the second profile.

6. The noise reducing device according to claim 1 , wherein said first local side surface ( 27 ) of at least the airflow modifying elements ( 20 ) has a tapered profile in a width direction and/or in a length direction.

7. The noise reducing device according to claim 1 , wherein at least the airflow modifying elements ( 20 ) are serrations.

8. The noise reducing device according to claim 7 , wherein the noise reducing elements ( 23 ) are serrations.

9. A wind turbine blade ( 5 ) for a wind turbine, extending in a longitudinal direction from a blade root ( 7 ) to a tip end ( 8 ) and further in a chordwise direction from a leading edge ( 9 ) to a trailing edge ( 10 ), the wind turbine blade comprising a first side surface defining a pressure side ( 12 ) and a second side surface defining a suction side ( 13 ), wherein at least one noise reducing device ( 19 ) according to claim 1 is attached to one of said first and second side surfaces, wherein the at least one noise reducing device ( 19 ) is arranged relative to the trailing edge ( 10 ), the trailing edge ( 10 ) being a truncated trailing edge ( 10 ″).

10. The wind turbine blade according to claim 9 , wherein at least the airflow modifying elements ( 20 ) or the at least one base part ( 26 ) of the at least one noise reducing device ( 19 ) is arranged on said one of the first and second side surfaces and extends towards the leading edge ( 9 ).

11. The wind turbine blade according to claim 9 , wherein the truncated trailing edge ( 10 ″) includes a trailing edge surface ( 32 ), and wherein the local edge surface ( 28 ) of the at least one noise reducing device ( 19 ) extends along at least part of said trailing edge surface ( 32 ) in a flapwise direction.

12. The noise reducing device according to claim 1 , wherein the local edge surface is arranged at or adjacent to the second proximal end ( 24 ).

13. A noise reducing device ( 19 ) for a wind turbine blade ( 5 ), having a first end ( 22 ), a second end ( 25 ), a first local side surface ( 27 ) and a second local side surface ( 29 ) arranged between the first end ( 22 ) and the second end, wherein the noise reducing device ( 19 ) is configured for attachment to a side surface of the wind turbine blade ( 5 ), the noise reducing device ( 19 ) comprising a plurality of airflow modifying elements ( 20 ), a plurality of noise reducing elements ( 23 ) and at least one base part ( 26 ), the airflow modifying elements ( 20 ) extending from a first proximal end ( 21 ) to the first end ( 22 ), the noise reducing elements ( 23 ) extending from an opposite facing second proximal end ( 24 ) to the second end ( 25 ), and the at least one base part ( 26 ) extending from the first proximal end ( 21 ) to the second proximal end ( 24 ), wherein the airflow modifying elements ( 20 ) and the noise reducing elements ( 23 ) extend in opposite longitudinal directions from the first end ( 22 ) to the second end ( 25 ), the second local side surface ( 29 ) of each of the airflow modifying elements ( 20 ) and the at least one base part ( 26 ) forming a continuous flat side surface and being configured to contact and/or to be directly attached to said side surface of the wind turbine blade ( 5 ), wherein the wind turbine blade ( 5 ) has a trailing edge ( 10 ), the trailing edge ( 10 ) being a truncated trailing edge ( 10 ″) having a trailing edge surface ( 32 ), and wherein the at least one noise reducing device ( 19 ) has a local edge surface ( 28 ) configured to extend along at least part of said trailing edge surface ( 32 ) in a flapwise direction when the noise reducing device ( 19 ) is attached to a side surface of the wind turbine blade ( 5 ).

14. The noise reducing device according to claim 13 , wherein each of the airflow modifying elements ( 20 ) has a first length measured from the first proximal end ( 21 ) to the first end ( 22 ) and each of the noise reducing elements ( 23 ) has a second length measured from the second proximal end ( 24 ) to the second end ( 25 ), wherein the first length is equal to or less than the second length.

15. The noise reducing device according to claim 13 , wherein each of the airflow modifying elements ( 20 ) has a first width measured along the first proximal end ( 21 ) and each of the noise reducing elements ( 23 ) has a second width measured along the second proximal end ( 24 ), wherein the first width is equal to or less than the second width.

16. The noise reducing device according to claim 13 , wherein said first local side surface ( 27 ) of at least the airflow modifying elements ( 20 ) has a tapered profile in a width direction and/or in a length direction.

17. A wind turbine blade ( 5 ) for a wind turbine, extending in a longitudinal direction from a blade root ( 7 ) to a tip end ( 8 ) and further in a chordwise direction from a leading edge ( 9 ) to a trailing edge ( 10 ), the wind turbine blade comprising a first side surface defining a pressure side ( 12 ) and a second side surface defining a suction side ( 13 ), wherein at least one noise reducing device ( 19 ) is attached to one of said first and second side surfaces, wherein the at least one noise reducing device ( 19 ) is arranged relative to the trailing edge ( 10 ), the noise reducing device ( 19 ) having a first end ( 22 ), a second end ( 25 ), a first local side surface ( 27 ) and a second local side surface ( 29 ) arranged between the first end ( 22 ) and the second end, the noise reducing device ( 19 ) comprising a plurality of airflow modifying elements ( 20 ), a plurality of noise reducing elements ( 23 ) and at least one base part ( 26 ), the airflow modifying elements ( 20 ) extending from a first proximal end ( 21 ) to the first end ( 22 ), the noise reducing elements ( 23 ) extending from an opposite facing second proximal end ( 24 ) to the second end ( 25 ), the at least one base part ( 26 ) extends from the first proximal end ( 21 ) to the second proximal end ( 24 ), wherein the airflow modifying elements ( 20 ) and the noise reducing elements ( 23 ) extend in opposite longitudinal directions from the first end ( 22 ) to the second end ( 25 ), the second local side surface ( 29 ) of each of the airflow modifying elements ( 20 ) and the at least one base part ( 26 ) forming a continuous flat side surface, wherein the trailing edge ( 10 ) is a truncated trailing edge ( 10 ″) having a trailing edge surface ( 32 ), wherein the at least one noise reducing device ( 19 ) has a local edge surface ( 28 ) extend along at least part of said trailing edge surface ( 32 ) in a flapwise direction.

18. The wind turbine blade according to claim 17 , wherein each of the airflow modifying elements ( 20 ) has a first length measured from the first proximal end ( 21 ) to the first end ( 22 ) and each of the noise reducing elements ( 23 ) has a second length measured from the second proximal end ( 24 ) to the second end ( 25 ), wherein the first length is equal to or less than the second length.

19. The wind turbine blade according to claim 17 , wherein each of the airflow modifying elements ( 20 ) has a first width measured along the first proximal end ( 21 ) and each of the noise reducing elements ( 23 ) has a second width measured along the second proximal end ( 24 ), wherein the first width is equal to or less than the second width.

20. The wind turbine blade according to claim 17 , wherein said first local side surface ( 27 ) of at least the airflow modifying elements ( 20 ) has a tapered profile in a width direction and/or in a length direction.