Nacelle test apparatus

1. A nacelle test apparatus for testing a wind turbine nacelle, comprising:

a physical tower model apparatus realised to model the behaviour of a wind turbine tower; and

a physical rotor model apparatus realised to model the behaviour of a wind turbine rotor, wherein the physical rotor model apparatus comprises a rotor hub exciter apparatus configured to model uneven or eccentric loading of a rotor, wherein the rotor hub exciter apparatus comprises a rotation mass mounted directly on a shaft; and

a tower model exciter for exciting a physical tower model apparatus.

2. The nacelle test apparatus according to claim 1 , wherein the tower exciter apparatus is realised to excite the physical tower model apparatus at a specific frequency or in a specific frequency range.

3. The nacelle test apparatus according to claim 1 , wherein the physical tower model apparatus comprises a yaw interface realised for securing the nacelle to the physical tower model apparatus.

4. The nacelle test apparatus according to claim 3 , wherein the yaw interface is realised to be adapted to a number of different nacelle designs.

5. The nacelle test apparatus according to claim 1 , wherein the physical tower model apparatus comprises,

a spring element arrangement realised to mimic spring characteristics of a wind turbine tower, and

a tower exciter apparatus realised to excite the spring element arrangement.

6. The nacelle test apparatus according to claim 5 , wherein the spring element arrangement comprises a plurality of upright spring elements.

7. The nacelle test apparatus according to claim 6 , wherein a spring element is realised to comprise a high stiffness in a vertical direction and a low stiffness in a horizontal direction.

8. The nacelle test apparatus according to claim 6 , wherein a spring element comprises a bundle of upright plates connected together.

9. The nacelle test apparatus according to claim 6 , further comprising a horizontal mounting plate for connecting to the upright spring elements of the spring element arrangement, and

wherein the tower exciter apparatus is realised to apply a lateral force to the horizontal mounting plate.

10. A method of testing a wind turbine nacelle, the method comprising:

mounting the nacelle onto a physical tower model apparatus of a nacelle test apparatus, which physical tower model apparatus is realised to model the behaviour of a wind turbine tower; and

mounting a physical rotor model apparatus of the nacelle test apparatus to a hub of the nacelle, which physical rotor model apparatus is realised to model the behaviour of a wind turbine rotor; and

exciting the physical tower model apparatus and the physical rotor model apparatus, wherein exciting the physical rotor model apparatus comprises using a rotor hub exciter apparatus configured to model uneven or eccentric loading of a rotor, wherein the rotor hub exciter apparatus comprises a rotation mass mounted directly on a shaft.

11. The method according to claim 10 , further comprising measuring a load exerted on a component in or on the nacelle as a result of an excitation of the physical tower model apparatus and the physical rotor model apparatus.

12. The method according to claim 10 , wherein the exciting the physical tower model apparatus comprises inducing a vibration of the physical tower model apparatus in a specific direction.

13. The method according to claim 12 , wherein the exciting the physical tower model apparatus comprises altering a direction of vibration of the physical tower model apparatus.

14. The method according to claim 12 , further comprising yawing the nacelle while subjecting the physical tower model apparatus to excitations in a plurality of directions.

15. A method of testing a wind turbine nacelle, the method comprising:

mounting the nacelle onto a physical tower model apparatus of a nacelle test apparatus, which physical tower model apparatus is realised to model the behaviour of a wind turbine tower; and

mounting a physical rotor model apparatus of the nacelle test apparatus to a hub of the nacelle, which physical rotor model apparatus is realised to model the behaviour of a wind turbine rotor; and

exciting the physical tower model apparatus and the physical rotor model apparatus, wherein exciting the physical rotor model apparatus comprises using a rotor hub exciter apparatus configured to model uneven or eccentric loading of a rotor, wherein the rotor hub exciter apparatus comprises a rotation mass mounted directly on a shaft and rotated in an eccentric manner using a drive belt.

16. The method according to claim 15 , further comprising measuring a load exerted on a component in or on the nacelle as a result of an excitation of the physical tower model apparatus and the physical rotor model apparatus.

17. The method according to claim 15 , wherein the exciting the physical tower model apparatus comprises inducing a vibration of the physical tower model apparatus in a specific direction.

18. The method according to claim 17 , wherein the exciting the physical tower model apparatus comprises altering a direction of vibration of the physical tower model apparatus.

19. The method according to claim 17 , further comprising yawing the nacelle while subjecting the physical tower model apparatus to excitations in a plurality of directions.