A wind turbine rotor blade comprising a blade root , a blade tip , a leading edge , a trailing edge , a first row of vortex generators and a second row of vortex generators, • wherein the first row and the second row extend in a generally spanwise direction and the first row is arranged closer to the leading edge than the second row , • wherein the first row comprises two adjacent vortex generators each having a longitudinal axis extending in a generally chordwise direction and two first fins arranged symmetrically to the longitudinal axis , wherein each of the two first fins has a leading end and a trailing end , wherein the trailing ends are arranged in a distance d from each other, wherein the distance d is larger than a distance between the leading ends , wherein the two longitudinal axes are arranged in a distance D from each other and define a centre line extending in a generally chordwise direction, • wherein the second row of vortex generators comprises a second fin having a leading end and a trailing end , wherein the trailing end is arranged closer to the centre line than the leading end , • wherein the second fin is positioned with reference to the first fin that is arranged on the same side of the centre line as the second fin and with its trailing end closer to the centre line than its leading end such that the trailing end of the second fin is arranged in a chordwise distance c from the trailing end of that first fin , characterised in that • the chordwise distance c is larger than twice the distance d and • a distance x of the trailing end of the second fin from the centre line is within the range between (i) an upper limit x U defined by: x U ≤ 0.30 D for c > 1.43 D - 3.57 d x U ≤ D/2 - d/2 - 0.14 c for c ≤ 1.43 D - 3.57 d and (ii) a lower limit x L defined by x L ≥ 0.07 D for c > 0.75 D - 0.87 d x L ≥ D/2 - d/2 - 0.58 c for c ≤ 0.75 D - 0.87 d. • wherein the first row and the second row extend in a generally spanwise direction and the first row is arranged closer to the leading edge than the second row , • wherein the first row comprises two adjacent vortex generators each having a longitudinal axis extending in a generally chordwise direction and two first fins arranged symmetrically to the longitudinal axis , wherein each of the two first fins has a leading end and a trailing end , wherein the trailing ends are arranged in a distance d from each other, wherein the distance d is larger than a distance between the leading ends , wherein the two longitudinal axes are arranged in a distance D from each other and define a centre line extending in a generally chordwise direction, • wherein the second row of vortex generators comprises a second fin having a leading end and a trailing end , wherein the trailing end is arranged closer to the centre line than the leading end , • wherein the second fin is positioned with reference to the first fin that is arranged on the same side of the centre line as the second fin and with its trailing end closer to the centre line than its leading end such that the trailing end of the second fin is arranged in a chordwise distance c from the trailing end of that first fin , characterised in that • the chordwise distance c is larger than twice the distance d and • a distance x of the trailing end of the second fin from the centre line is within the range between (i) an upper limit x U defined by: x U ≤ 0.30 D for c > 1.43 D - 3.57 d x U ≤ D/2 - d/2 - 0.14 c for c ≤ 1.43 D - 3.57 d and (ii) a lower limit x L defined by x L ≥ 0.07 D for c > 0.75 D - 0.87 d x L ≥ D/2 - d/2 - 0.58 c for c ≤ 0.75 D - 0.87 d. (i) an upper limit x U defined by: x U ≤ 0.30 D for c > 1.43 D - 3.57 d x U ≤ D/2 - d/2 - 0.14 c for c ≤ 1.43 D - 3.57 d and (ii) a lower limit x L defined by x L ≥ 0.07 D for c > 0.75 D - 0.87 d x L ≥ D/2 - d/2 - 0.58 c for c ≤ 0.75 D - 0.87 d. <EOS>