Wind turbine blade provided with flow altering devices

A blade for a rotor of a wind turbine having a substantially horizontal rotor shaft, the rotor comprising a hub, from which the blade extends substantially in a radial direction when mounted to the hub, the blade having a predetermined target axial induction factor at a rotor design point, the blade comprising:

• a profiled contour comprising a pressure side and a suction side as well as a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, the profiled contour generating a lift when being impacted by an incident airflow,
• the profiled contour in the radial direction being divided into a root region with a substantially circular or elliptical profile closest to the hub, an airfoil region with a lift generating profile furthest away from the hub, and preferably a transition region between the root region and the airfoil region, the transition region having a profile gradually changing in the radial direction from the circular or elliptical profile of the root region to the lift generating profile of the airfoil region, characterised in that
• the airfoil region is divided into a number of base sections, a first one of said base sections extending along at least 20% of a longitudinal extent of the airfoil region, the first base section having a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge,
• the first base section being formed so as deviate at least 5% from the target axial induction factor at the rotor design point, and
• the first base section being provided with a number of first flow altering devices arranged so as to adjust the aerodynamic properties and substantially meet the target axial induction factor at the rotor design point.

A method of designing a blade with a predetermined target axial induction factor at a rotor design point for a rotor of a wind turbine having a substantially horizontal rotor shaft, the rotor comprising a hub, from which the blade extends substantially in a radial direction when mounted to the hub, the blade comprising:

• a profiled contour comprising a pressure side and a suction side as well as a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, the profiled contour generating a lift when being impacted by an incident airflow,
• the profiled contour in the radial direction being divided into a root region with a substantially circular or elliptical profile closest to the hub, an airfoil region with a lift generating profile furthest away from the hub, and preferably a transition region between the root region and the airfoil region, the transition region having a profile gradually changing in the radial direction from the circular or elliptical profile of the root region to the lift generating profile of the airfoil region, wherein
• the airfoil region comprises at least a first longitudinal segment extending along at least 20% of a longitudinal extent of the airfoil region, the first longitudinal segment comprising a first base part having a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, characterised by
• designing the first base part with an axial induction factor deviating at least 5% from the target axial induction factor at the rotor design point, and
• designing and arranging a number of first flow altering devices at the first longitudinal section so as to adjust the aerodynamic properties of the first longitudinal segment to substantially meet the target axial induction factor at the rotor design point.

A method of modifying a blade for a rotor of a wind turbine having a substantially horizontal rotor shaft, the rotor comprising a hub, from which the blade extends substantially in a radial direction when mounted to the hub, the blade comprising:

• a profiled contour comprising a pressure side and a suction side as well as a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, the profiled contour generating a lift when being impacted by an incident airflow,
• the profiled contour in the radial direction being divided into a root region with a substantially circular or elliptical profile closest to the hub, an airfoil region with a lift generating profile furthest away from the hub, and preferably a transition region between the root region and the airfoil region, the transition region having a profile gradually changing in the radial direction from the circular or elliptical profile of the root region to the lift generating profile of the airfoil region, wherein
• the airfoil region comprises at least a first longitudinal segment extending along at least 20% of a longitudinal extent of the airfoil region, the first longitudinal segment comprising a first base part having a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, characterised by
• the first base part being designed with an axial induction factor, which without flow altering device deviates at least 5% from a target axial induction factor at a design point, and
• modifying the first longitudinal segment by providing a number of first flow altering devices arranged so as to adjust the aerodynamic properties of the first longitudinal segment to substantially meet the target axial induction factor at the design point.