OpenFAST AeroDyn v15 Convergence Error

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Sam.Ramsahoye
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OpenFAST AeroDyn v15 Convergence Error

Postby Sam.Ramsahoye » Tue Nov 10, 2020 4:17 pm

Hello,

I'm using OpenFAST v2.3.0.

I'm having a couple of issues with AeroDyn. I have designed a turbine model around the 15MW reference turbine. I have tuned a controller and I'm running fully aero-elastic simulations in OpenFAST. Each of my simulations are an hour long, there are 22 in total (4-26m/s, 5.5% turbulence at v=15 m/s)

Depending on my exact setup, sometimes I get failures on a few of the higher wind-speed simulations, I think due to convergence of AeroDyn. Normally the error messages OpenFAST gives are super helpful, however this one was less so - I have attached the error (error.png). The simulations are stable up until this point with no apparent misbehaviour of the controller.

I read on some of the other posts that people have had issues running AeroDyn when they end up with a negative horizontal local velocity. In the same posts, it was hypothesised that changing the tower potential flow correction between 1,2 can improve things and also increasing the time-step.

What is odd to me is that the error only occurs at node 1 the first blade - I have attached the blade node definition (AeroDynBladeNode.png), the airfoil reference is too a cylindrical section. Given that the solutions are stable otherwise, I think it's highly unlikely that the fore-aft motion is sufficiently high to cause a negative velocity (it would have to be approximately 20 m/s in magnitude at the tower top).

Any thoughts would be greatly appreciated :)

Best,
Sam
Attachments
error.PNG
error.PNG (16.64 KiB) Viewed 378 times
AeroDynBladeNode.PNG
AeroDynBladeNode.PNG (16.08 KiB) Viewed 378 times

Jason.Jonkman
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Re: OpenFAST AeroDyn v15 Convergence Error

Postby Jason.Jonkman » Tue Nov 10, 2020 5:22 pm

Dear Sam,

I asked Andy Platt, and here is his response:

I suspect that is due to some broken error handling that was fixed in v2.4.0 with this PR: https://github.com/OpenFAST/openfast/pull/435

Does upgrading to OpenFAST v2.4 solve the problem?

Best regards,
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

Sam.Ramsahoye
Posts: 22
Joined: Mon Apr 27, 2020 1:06 pm
Organization: Arup
Location: United Kingdom

Re: OpenFAST AeroDyn v15 Convergence Error

Postby Sam.Ramsahoye » Wed Nov 11, 2020 12:37 pm

Hi Jason,

Thanks very much for getting back to me. It looks like Andrew found this error when using the 15MW IEA airfoils. When I tuned my model based on a different set of airfoils, the problem went away but I'll try Andrew's fix anyway.

Best,
Sam


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