Wind turbine blade comprising a trailing edge noise reducing device

A method of retrofitting a noise reducing device on a wind turbine blade, comprising:

• providing a wind turbine blade (5) extending in a longitudinal direction from a blade root (7) to a tip end (8) and in a chordwise direction from a leading edge (9) to a trailing edge (10), the wind turbine blade (5) comprises an aerodynamic profile having a first side surface and a second side surface, wherein at least one noise reducing device (19) is arranged on the first or second side surface or on a trailing edge surface (31), the at least one noise reducing device (19) has a first end (21), a second end (22), a first side surface (20), and a second side surface (27), the noise reducing device (19) further comprises a base part (23) and at least one array of first noise reducing elements (25) extending from a proximal end (24) to the second end (22), the base part (23) extends from the first end (21) to the proximal end (24), wherein the method further comprises the steps of:
• positioning at least one array of second noise reducing elements (26) on the base part (23), the at least one array of second noise reducing elements (26) being separate from the at least one array of first noise reducing elements (25), wherein the at least one array of first noise reducing elements (25) are serrations and the at least one array of second noise reducing elements (26) are bristles, the serrations and the bristles being arranged such that the serrations lie within, and extend within, a first plane, and the bristles substantially lie within, and substantially extend within, a second plane, wherein the first plane and the second plane are parallel and spaced apart from one another, the serrations and bristles being further arranged such that each of the serrations extends from the proximal end (24), and each of the bristles projects from an attachment line extending parallel to the proximal end (24), wherein the attachment line is positioned between the proximal end (24) and the first end (21), the attachment line being nearer the proximal end (24) than the first end (21);
• and
• attaching said at least one array of second noise reducing elements (26) to the base part (23) so that a free end of the at least one array of second noise reducing elements (26) substantially faces towards said second end (22) in a non-loaded condition.

A method of manufacturing a noise reducing device for a wind turbine blade, comprising:

• manufacturing a noise reducing device (19) having a first end (21), a second end (22), a first side surface (20), and a second side surface (27), wherein the noise reducing device (19) comprises a base part (23) configured for attachment to a side surface or a trailing edge surface (31) of the wind turbine blade (5), and at least one array of first noise reducing elements (25) extending from a proximal end (24) to the second end (22), wherein the base part (23) extends from the first end (21) to said proximal end (24), wherein the method further comprises the steps of:
• manufacturing at least one array of second noise reducing elements (26), the at least one array of second noise reducing elements (26) have a free end, the at least one array of second noise reducing elements (26) being separate from the at least one array of first noise reducing elements (25);
• positioning said at least one array of second noise reducing elements (26) on the base part (23), wherein the at least one array of first noise reducing elements (25) are serrations and the at least one array of second noise reducing elements (26) are bristles, the serrations and the bristles being arranged such that the serrations lie within, and extend within, a first plane, and the bristles substantially lie within, and substantially extend within, a second plane, wherein the first plane and the second plane are parallel and spaced apart from one another, the serrations and bristles being further arranged such that each of the serrations extends from the proximal end (24), and each of the bristles projects from an attachment line extending parallel to the proximal end (24), wherein the attachment line is positioned between the proximal end (24) and the first end (21), the attachment line being nearer the proximal end (24) than the first end (21);
• and
• attaching the at least one array of second noise reducing elements (26) to the base part (23) so that the free end substantially faces towards said second end (22) in a non-loaded condition.