Wind turbine blade having a longitudinal direction with a root end and a tip end as well as a chord extending In a transverse direction between a leading edge and a trailing edge, the blade comprising a flow control surface with a suction side and a pressure side, wherein a number of boundary layer control means is formed in the flow control surface, wherein the boundary layer control means Include a channel submerged in the flow control surface (112; 212; 312; 412; 512; 612) with a first end (102; 202; 302; 402; 502; 602) facing towards the leading edge and a second end (104; 204; 304; 404; 504; 604) facing towards the trailing edge of the blade, the channel comprising: - a bottom surface (106; 206; 306; 606) extending from the first end (102; 202; 302; 402; 502; 602) to the second end (104; 204; 304; 404; 504; 604), - a first sidewall (108; 208; 308; 408; 508; 608) extending between the flow control surface (112; 212; 312; 412; 512; 612) and the bottom surface (106; 206; 306; 606) and extending between the first end (102; 202; 302; 402; 502; 602) and the second end (104; 204; 304; 404; 504; 604), the first sidewall (108; 208; 308; 408; 508; 608) forming a first sidewall edge (114; 214; 314) between the first side wall (108; 208; 308; 408; 508; 608) and the flow control surface (112; 212; 312; 412; 512; 612), and - a second sidewall (110; 210; 310; 410; 510; 610) extending between the flow control surface (112; 212; 312; 412; 512; 612) and the bottom surface (106; 206; 306; 606) and extending between the first end (102; 202; 302; 402; 502; 602) and the second end (104; 204; 304; 404; 504; 604), the second sidewall (110; 210; 310; 410; 510; 610) forming a second sidewall edge (116; 216; 316) between the second side wall (110; 210; 310; 410; 510; 610) and the flow control surface (112; 212; 312; 412; 512; 612), characterised in that - the channel at the first end (102; 202; 302; 402; 502; 602) comprises a first flow accelerating channel zone (122; 222; 322; 622) adapted for accelerating a flow, and at the second end (104; 204; 304; 404; 504; 604) comprises a second channel zone (124; 224; 324; 624), where the first sidewall (108; 208; 308; 408; 608; 608) and the second sidewall (110; 210; 310; 410; 510; 610) are diverging towards the trailing edge of the blade. - a bottom surface (106; 206; 306; 606) extending from the first end (102; 202; 302; 402; 502; 602) to the second end (104; 204; 304; 404; 504; 604), - a first sidewall (108; 208; 308; 408; 508; 608) extending between the flow control surface (112; 212; 312; 412; 512; 612) and the bottom surface (106; 206; 306; 606) and extending between the first end (102; 202; 302; 402; 502; 602) and the second end (104; 204; 304; 404; 504; 604), the first sidewall (108; 208; 308; 408; 508; 608) forming a first sidewall edge (114; 214; 314) between the first side wall (108; 208; 308; 408; 508; 608) and the flow control surface (112; 212; 312; 412; 512; 612), and - a second sidewall (110; 210; 310; 410; 510; 610) extending between the flow control surface (112; 212; 312; 412; 512; 612) and the bottom surface (106; 206; 306; 606) and extending between the first end (102; 202; 302; 402; 502; 602) and the second end (104; 204; 304; 404; 504; 604), the second sidewall (110; 210; 310; 410; 510; 610) forming a second sidewall edge (116; 216; 316) between the second side wall (110; 210; 310; 410; 510; 610) and the flow control surface (112; 212; 312; 412; 512; 612), characterised in that - the channel at the first end (102; 202; 302; 402; 502; 602) comprises a first flow accelerating channel zone (122; 222; 322; 622) adapted for accelerating a flow, and at the second end (104; 204; 304; 404; 504; 604) comprises a second channel zone (124; 224; 324; 624), where the first sidewall (108; 208; 308; 408; 608; 608) and the second sidewall (110; 210; 310; 410; 510; 610) are diverging towards the trailing edge of the blade.