Wind turbine blade with multiple spar caps

1. A wind turbine blade comprising:

an aerodynamic shell ( 62 ) having an outer surface ( 64 ) forming at least part of an exterior surface of the wind turbine blade and an inner surface ( 66 );

a recess ( 70 ) at the inner surface ( 66 ) of the aerodynamic shell, the recess ( 70 ) extending within the shell along a spanwise direction of the blade, wherein the recess ( 70 ) comprises a first region ( 72 ) having a first width, a second region ( 74 ) having a second width exceeding the first width, and a transition region ( 73 ) connecting the first region ( 72 ) with the second region ( 74 ) of the recess ( 70 ), wherein a width of the transition region ( 73 ) tapers from the second region ( 74 ) towards the first region ( 72 ); and

a load carrying structure comprising a first and a second spar cap ( 80 , 82 ) extending within the shell ( 62 ) along a spanwise direction of the blade, wherein the first spar cap ( 80 ) is arranged at least partly in the recess ( 70 ) of the aerodynamic shell, and wherein the second spar cap ( 82 ) is arranged on top of at least part of the first spar cap ( 80 ).

2. The wind turbine blade according to claim 1 , wherein the second spar cap ( 82 ) is wider than the first spar cap ( 80 ).

3. The wind turbine blade according to claim 1 , wherein the shell comprises a pressure side shell half and a suction side shell half, each of the shell halves comprising a recess ( 70 ) and a load carrying structure according to claim 1 .

4. The wind turbine blade according to claim 1 , wherein the first and second spar caps ( 80 , 82 ) each comprise a fabric, wherein the fabric of the first spar cap ( 80 ) is different from the fabric of the second spar cap ( 82 ).

5. The wind turbine blade according to claim 1 , wherein the first width of the first region is within a range of 35-90% of the second width of the second region.

6. The wind turbine blade according to claim 1 , wherein the difference between the first width of the first region and the second width of the second region is in a range of 50-800 mm.

7. The wind turbine blade according to claim 1 , wherein the spanwise extent of the transition region is 0.5-5 meters.

8. The wind turbine blade according to claim 1 , wherein the first and/or second spar cap ( 80 , 82 ) comprise a hybrid carbon/glass fibre material.

9. The wind turbine blade according to claim 1 , wherein the recess ( 70 ) is substantially bottle-shaped.

10. The wind turbine blade according to claim 1 , wherein the aerodynamic shell comprises a first thickened portion laterally adjoining the recess ( 70 ) at a first side of the recess ( 70 ) and a second thickened portion laterally adjoining the recess ( 70 ) at a second side of the recess ( 70 ).

11. The wind turbine blade according to claim 10 , wherein the first thickened portion and/or the second thickened portion are formed as a sandwich structure comprising a number of outer skin layers, a number of inner skin layers, and an intermediate sandwich core material.

12. The wind turbine blade according to claim 1 , wherein the recess ( 70 ) has a base ( 71 ) and two opposing side walls ( 76 a , 76 b ), each side wall having a respective upper edge ( 76 a , 76 b ), wherein the transition region ( 73 ) of the recess has a proximal end and a distal end, seen in the spanwise direction, wherein an angle (Δ) is formed between the base ( 71 ) of the recess ( 70 ) and a line extending from the upper edge ( 76 a ) of a side wall ( 70 a ) at the proximal end of the transition region to an intersection between the base ( 71 ) and the respective sidewall ( 70 a ) at the distal end of the transition region ( 73 ), wherein said angle is between 0.2-20 degrees.

13. The wind turbine blade according to claim 12 , wherein the side walls ( 76 a , 76 b ) of the recess ( 70 ) are chamfered.

14. The wind turbine blade according to claim 1 , wherein the first spar cap ( 80 ) and the second spar cap ( 82 ) each are pre-manufactured as a fibre-reinforced object comprising a fibre reinforcement material and a matrix material.

15. A method of manufacturing a wind turbine blade, wherein the method comprises the steps of:

manufacturing an aerodynamic shell comprising a recess ( 70 ) at the inner surface of the aerodynamic shell, the recess ( 70 ) extending within the shell along a spanwise direction of the blade, wherein the recess ( 70 ) comprises a first region having a first width, a second region having a second width exceeding the first width, and a transition region connecting the first region with the second region of the recess ( 70 ), wherein a width of the transition region tapers from the second region towards the first region;

arranging a first spar cap ( 80 ) in the shell such that it extends within the shell along a spanwise direction of the blade, wherein the first spar cap ( 80 ) is arranged at least partly in the recess ( 70 ) of the aerodynamic shell;

bonding the first spar cap ( 80 ) to the shell;

arranging a second spar cap ( 82 ) on top of at least part of the first spar cap ( 80 ); and

bonding the second spar cap ( 82 ) to the first spar cap ( 80 ).