Rotor blade of a wind turbine

Abstract

A rotor blade of a wind turbine with a raked tip portion is provided. The tip portion is raked, i.e. curved, in a rotor blade plane comprising the tip base chord and a line which is parallel to the pitch axis of the rotor blade. Additionally, the orientation of the chords with reference to the chord at the tip base changes between the tip base and the tip. In other words, the trailing edge of the tip portion is twisted. Optionally, the tip portion is additionally swept out of the rotor blade plane, which is characterized by a cant angle.

1 . A rotor blade of a wind turbine, comprising
 a blade body extending between a root portion of the rotor blade and a tip portion of the rotor blade, a trailing edge and a leading edge,   wherein the rotor blade is arranged and prepared for being mounted to a hub of the wind turbine and for being pitched about a pitch axis, and   wherein a rotor blade plane is defined by the plane comprising the chord at the tip base and a line which is parallel to the pitch axis, wherein the tip base is the part of the rotor blade at which the tip portion joins the blade body,   wherein the trailing edge of the tip portion has a curved shape as projected on the rotor blade plane such that a trailing edge sweep angle increases from the tip base to the tip of the rotor blade, and   wherein orientation of the chords with reference to the chord at the tip base changes between the tip base and the tip such that a chord tilt angle changes between the tip base and the tip.   
     
     
         2 . The rotor blade according to  claim 1 , wherein the trailing edge sweep angle increases by at least 2 degrees from the tip base to the tip. 
     
     
         3 . The rotor blade according to  claim 1 , wherein the trailing edge sweep angle increases by at most 40 degrees from the tip base to the tip. 
     
     
         4 . The rotor blade according to  claim 1 , wherein the chord tilt angle varies by at least 2 degrees between the tip base and the tip. 
     
     
         5 . The rotor blade according to  claim 1 , wherein the chord tilt angle varies by at most 30 degrees between the tip base and the tip. 
     
     
         6 . The rotor blade according to  claim 1 , wherein
 in a first section of the tip portion the trailing edge is twisted towards the suction side of the blade body, thus leading to negative chord tilt angles and/or   in a second section of the tip portion the trailing edge is twisted towards the pressure side of the blade body, thus leading to positive chord tilt angles.   
     
     
         7 . The rotor blade according to  claim 6 , wherein the first section is adjacent to the tip base and the second section is adjacent to the tip. 
     
     
         8 . The rotor blade according to  claim 6 , wherein the rate of decrease of the chord length of the tip portion is greater in the second section than in the first section. 
     
     
         9 . The rotor blade according to  claim 1 , wherein the leading edge of the tip portion has a curved shape as projected on the rotor blade plane such that a leading edge sweep angle increases from the tip base to the tip. 
     
     
         10 . The rotor blade according to  claim 9 , wherein the leading edge sweep angle increases by at least 10 degrees from the tip base to the tip. 
     
     
         11 . The rotor blade according to  claim 9 , wherein the leading edge sweep angle increases by at most 80 degrees, in particular by at most 60 degrees, from the tip base to the tip. 
     
     
         12 . The rotor blade according to  claim 1 , wherein the tip portion is curved towards the trailing edge of the blade body. 
     
     
         13 . The rotor blade according to  claim 1 , wherein, as viewed from the suction side of the rotor blade,
 the trailing edge of the tip portion is concavely shaped and   the leading edge of the tip portion is convexly shaped.   
     
     
         14 . The rotor blade according to  claim 1 , wherein the trailing edge of the tip portion as projected on a reference plane, wherein the reference plane is defined as the plane comprising the pitch axis and being perpendicular to the chord at the tip base, has a curved shape such that a cant angle increases from the tip base to the tip. 
     
     
         15 . The rotor blade according to  claim 14 , wherein the cant angle increases by at least 20 degrees from the tip base to the tip. 
     
     
         16 . The rotor blade according to  claim 14 , wherein the trailing edge sweep angle and/or the cant angle increases monotonically from the tip base to the tip. 
     
     
         17 . The rotor blade according to  claim 1 , wherein
 at least one segment of the trailing edge of the tip portion is shaped as a straight line and/or   at least one segment of the leading edge of the tip portion is shaped as a straight line.   
     
     
         18 . The rotor blade according to  claim 1 , wherein the length of the tip portion, as projected on the rotor blade plane and measured along the pitch axis, is between 0.5% and 10%, of the length of the entire rotor blade as projected on the rotor blade plane and measured along the pitch axis. 
     
     
         19 . The rotor blade according to  claim 1 , wherein the rotor blade is shaped such that the tip is separated from a tangential plane which is defined to be perpendicular to the pitch axis and tangential to the tip portion. 
     
     
         20 . The rotor blade according to  claim 14 , wherein the rotor blade deforms under wind loads such that the trailing edge sweep angle and/or the chord tilt angle and/or the cant angle changes at least about 5% compared to an unloaded state of the rotor blade. 
     
     
         21 . The rotor blade according to  claim 1 ,
 wherein the tip portion is added to the blade body as a retrofit.   
     
     
         22 . The rotor blade according to  claim 1 , wherein the rotor blade is manufactured as a single piece. 
     
     
         23 . The rotor blade according to  claim 1 , wherein the trailing edge and the streamline of an airflow which flows from the leading edge across the rotor blade comprise an angle which is smaller than 80 degrees at the tip portion.