A wind turbine blade for a rotor of a wind turbine having a substantially horizontal rotor shaft, the rotor comprising a hub, from which the wind turbine blade extends substantially in a radial direction when mounted to the hub, the wind turbine blade extending in a longitudinal direction parallel to a longitudinal axis and having a tip end and a root end, the wind turbine blade further comprising a profiled contour including a pressure side and a suction side, as well as a leading edge (18, 56) and a trailing edge (20, 58) with a chord having a chord length extending there between, the profiled contour, when being impacted by an incident airflow, generating a lift, the wind turbine blade further comprising at least a first longitudinal section (36, 38) having a cross section with a first plurality of projecting elements provided at the trailing edge (20, 58) on said pressure side, said first plurality of projecting elements forming a first serrated trailing edge of the wind turbine blade, wherein said first plurality of projecting elements are arranged to perform a first modulation operation of a boundary layer flow of the pressure side of the blade, the first longitudinal section further has a second plurality of projecting elements (70") provided at the trailing edge (20, 58) on said suction side, said second plurality of projecting elements (70") forming a second serrated trailing edge of the wind turbine blade, said first plurality spaced from said second plurality (70") in a flapwise direction, wherein said second plurality of projecting elements (70") are arranged to perform a second modulation operation of a boundary layer flow of the suction side of the blade, said first and second modulation operations operable to reduce the operational noise of the wind turbine blade, and wherein said first plurality of projecting elements and said second plurality of projecting elements (70") are arranged such that said first modulation operation is different to said second modulation operation the wind turbine blade further comprising a profiled contour including a pressure side and a suction side, as well as a leading edge (18, 56) and a trailing edge (20, 58) with a chord having a chord length extending there between, the profiled contour, when being impacted by an incident airflow, generating a lift, the wind turbine blade further comprising at least a first longitudinal section (36, 38) having a cross section with a first plurality of projecting elements provided at the trailing edge (20, 58) on said pressure side, said first plurality of projecting elements forming a first serrated trailing edge of the wind turbine blade, wherein said first plurality of projecting elements are arranged to perform a first modulation operation of a boundary layer flow of the pressure side of the blade, the first longitudinal section further has a second plurality of projecting elements (70") provided at the trailing edge (20, 58) on said suction side, said second plurality of projecting elements (70") forming a second serrated trailing edge of the wind turbine blade, said first plurality spaced from said second plurality (70") in a flapwise direction, wherein said second plurality of projecting elements (70") are arranged to perform a second modulation operation of a boundary layer flow of the suction side of the blade, said first and second modulation operations operable to reduce the operational noise of the wind turbine blade, and wherein said first plurality of projecting elements and said second plurality of projecting elements (70") are arranged such that said first modulation operation is different to said second modulation operation