Blade Azimuth, Tower Potential Flow and Shaft Tilt

Discuss the theory and modeling of rotor aerodynamics.

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Francesco.Caccia
Posts: 6
Joined: Mon Apr 13, 2020 10:39 am
Organization: Politecnico di Milano
Location: Italy

Blade Azimuth, Tower Potential Flow and Shaft Tilt

Postby Francesco.Caccia » Fri Sep 25, 2020 10:02 am

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.
4) 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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Francesco.Caccia
Posts: 6
Joined: Mon Apr 13, 2020 10:39 am
Organization: Politecnico di Milano
Location: Italy

Re: Blade Azimuth, Tower Potential Flow and Shaft Tilt

Postby Francesco.Caccia » Fri Sep 25, 2020 10:38 am

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

Jason.Jonkman
Posts: 5737
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: Blade Azimuth, Tower Potential Flow and Shaft Tilt

Postby Jason.Jonkman » Fri Sep 25, 2020 10:43 am

Hi Francesco,

I was just going to respond with a link to viewtopic.php?f=4&t=1680. You beat me to the punch!

Thanks,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov


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