| CPC F03D 1/0675 (2013.01) [F05B 2240/122 (2013.01); F05B 2240/304 (2020.08); F05B 2240/305 (2020.08); F05B 2240/3062 (2020.08); F05B 2240/311 (2013.01)] | 20 Claims |

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1. A wind turbine blade comprising a plurality of add-on elements, which are arranged on an outer surface of the blade, wherein the plurality of add-on elements comprises at least one flexible add-on element and at least one stiff add-on element of the same add-on element type, wherein the at least one flexible add-on element consists at least predominantly of an elastic material and the at least one stiff add-on element consists at least predominantly of a stiff material, which is stiffer than the elastic material, wherein the at least one flexible add-on element and the at least one stiff add-on element are arranged offset in a span-wise direction and/or in a chord-wise direction of the blade,
wherein one or more flexible add-on elements of the at least one flexible add-on element are arranged in a surface portion of the blade, which has a span-wise length between 1 m and 5 m and extends in the chord-wise direction at least partly around an outer circumference of the blade, wherein a center of the surface portion in the span-wise direction is distanced from a root-side end of the blade between 33% and 50% of the span-wise length of the blade, wherein the at least one stiff add-on element is arranged outside of the surface portion.
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