A wind turbine blade for a rotor of a wind turbine having a substantially horizontal rotor shaft, said rotor comprising a hub, from which the blade extends substantially in a radial direction when mounted to the hub, the blade having a longitudinal direction with a tip end and a root end and a transverse direction, the blade further comprising: a profiled contour including a pressure side and a suction side, as well as a leading edge and a trailing edge with a chord line having a chord length extending there between, the chord line transverse to said longitudinal direction, the profiled contour, when being impacted by an incident air-flow, generating a lift, wherein the wind turbine further comprises first and second flow guide members (70, 72, 80, 84, 90, 92, 100, 110, 112) provided on a surface of said wind turbine blade, wherein said first and second flow guide members extend in a direction substantially transverse to the longitudinal direction of the blade, said first and second flow guide members defining a flow channel between said leading edge and said trailing edge, said flow channel having a first end located towards said leading edge and a second end located towards said trailing edge, wherein at least a portion of one of said first and second flow guide members extends along the transverse direction of said blade at an angle to said chord line of approximately 15 to 60 degrees, and wherein said flow channel comprises at least one constricted section spaced from said first end towards said second end, wherein the distance between said first and second flow guide members at said at least one constricted section is less than the distance between said first and second flow guide members at the first end of said flow channel, such that attached flow in said flow channel between said first and second flow guide members from said first end to said second end is subjected to a Venturi effect by said at least one constricted section. a profiled contour including a pressure side and a suction side, as well as a leading edge and a trailing edge with a chord line having a chord length extending there between, the chord line transverse to said longitudinal direction, the profiled contour, when being impacted by an incident air-flow, generating a lift, wherein the wind turbine further comprises first and second flow guide members (70, 72, 80, 84, 90, 92, 100, 110, 112) provided on a surface of said wind turbine blade, wherein said first and second flow guide members extend in a direction substantially transverse to the longitudinal direction of the blade, said first and second flow guide members defining a flow channel between said leading edge and said trailing edge, said flow channel having a first end located towards said leading edge and a second end located towards said trailing edge, wherein at least a portion of one of said first and second flow guide members extends along the transverse direction of said blade at an angle to said chord line of approximately 15 to 60 degrees, and wherein said flow channel comprises at least one constricted section spaced from said first end towards said second end, wherein the distance between said first and second flow guide members at said at least one constricted section is less than the distance between said first and second flow guide members at the first end of said flow channel, such that attached flow in said flow channel between said first and second flow guide members from said first end to said second end is subjected to a Venturi effect by said at least one constricted section.