Blade Azimuth, Tower Potential Flow and Shaft Tilt

Wind & Water Rotor Aerodynamics
1

Dear all,
I’m just starting to use AeroDyn to become familiar with the software before switching to OpenFAST.
I’ve noticed some strange behaviour of blade azimuth. Since the rotor speed is fixed to 12.1 rpm, I am expecting to find a linear behaviour of the blade azimuth; however, the actual behaviour depends on the presence of the tower potential flow and on the shaft tilt angle.
The following results are obtained for WndSpeed=12 m/s; ShearExp=0; RotSpeed=12.1 rpm; Pitch=0 deg; Yaw=0 deg; dT=1.38000E-02 s. I’m using the 5MW model.

I’ve analysed four different cases, with precone always set to zero:

  1. Shaft Tilt = 0°; w/o potential flow;
  2. Shaft Tilt = 0°; w/ potential flow;
  3. Shaft Tilt = 5°; w/o potential flow;
  4. Shaft Tilt = 5°; w/ potential flow.

The expected behaviour is obtained only for case 3). In the other cases, results look odd to me. In particular:

  1. blade azimuth is constant, with some spikes.
  2. blade azimuth is piece-wise linear.
  3. blade azimuth is linear, unless any of the blade is crossing the tower (@ psi = -90°).

I’ve attached images of the results. Blue refers to blade1, red to blade2, yellow to blade3.
How can this behaviour be explained?

Best Regards,
Francesco

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2

I guess the answer is provided in this topic: viewtopic.php?f=4&t=1680 . I’m still leaving this as a reference for searchers, if it can be useful. Otherwise it can be deleted.

Francesco

3

Hi Francesco,

I was just going to respond with a link to Azimuth Angle of the Blade. You beat me to the punch!

Thanks,