About the wind turbine loads

Wind & Water Computer-Aided Engineering Software Tools
1

Dear Jason,

I have a question about the wind turbine loads. As I know, the 2p loads in the three blade root bending moments will lead to the 3p loads in the tilt and yaw moments.
When I reduce the 2p loads on the blade using individual pitch control, the 3p load in the tilt moment decreases. however, the 3p load in the yaw moment increases, which i cannot interpret.

When I mitigate the 4p components of the blade root bending moments, the similar result can be obtained.

But when I mitigate both 2p and 4p components of the blade root bending moment, both the 3p components of the tilt and yaw moments will decrease.

Is this result right or wrong? Looking forward to your reply. Thanks a lot.

Best regards,
Yunqian Zhang

2

Dear Yunqian Zhang,

You are correct that 2p-cyclic loads in the rotating frame contribute to 0p and 3p loading in the nonrotating frame for a 3-bladed turbine, which suggests that a reduction in 2p loads in the rotating frame would reduce 3p loading in the nonrotating frame. If your results are not fully consistent with this, have you assessed all six load components in the rotating frame? (The six load components are: in-plane and out-of-blane shear forces, axial forces, in-plane and out-of-plane bending moments, and pitching moment.) For example, the nacelle-yaw moment may not only be influenced by blade-bending, but also by the blade pitching moment; perhaps bending is being reduced but the pitching moment is increased?

Perhaps someone with more experience with the application of linear models and/or multi-blade-coordinate (MBC) transformations can provide further guidance.

Best regards,

3

Dear Dr. Jason,

I have one question regaring loads applied on the wind turbine. I understand that the blades are divided to small segments along the blade length and by blade element momentum theory the thrust and torque forces are integrated. what I don’t understand is how 1P and 3P loads are considered, I read in the Aerodyn manual that there is a tower shadow model based on potential flow around a cylinder and an expanding wake. what about 1P loading , is it force or moment and where is applied?

Regards,

Marwa

4

Dear @Marwa.Mohamed,

Aerodynamic excitations at multiples of the rotor speed happens naturally in the OpenFAST solve through the use of wind conditions local to each blade element. For example, a tower shadow will cause 1P excitation of the blade in the rotating frame of reference (within the blade) and a 3P excitation of the tower (because each of the 3 blades will pass through the shadow each revolution).

Best regards,

5

Thanks Dr. Jason for your reply.

So, every time the blade passes the tower, there will be dip in the blade thrust every revolution (1p). and the tower 3 dips per revolution (3p) one from each blade, is my understanding right?

will they appear as (1p= force and moment at the rotor level) and the (3p as force and moment along the tower and the tower base)?

Regards,

Marwa

6

Dear @Marwa.Mohamed,

Yes, I agree. Moreover, the tower shadow may induce higher harmonics (1P, 2P, 3P, etc. in the blade; 3P, 6P, etc. in the tower) due to nonlinearities in the solution, although 1P in the blade and 3P in the tower will be stronger than the other harmonics.

Best regards,