Airfoil Prep - 3D corrections

Discuss acquisition, use, and manipulation of airfoil data.

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Majjari.Chaitanya
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Organization: Fraunhoffer Gesellschaft
Location: Germany

Airfoil Prep - 3D corrections

Postby Majjari.Chaitanya » Mon Dec 05, 2016 2:57 am

Hello Everyone,
I'm working on the Adaptive trailing edge flap dynamic stall model(A beddoes Leishman type dynamic stall model). I have to implement this model in OneModelica library simulation tool. In order to validate the model, I have generated the steady airfoil coefficients for DU21 airfoil, at different flap angles. Then I have used the Airfoil prep to extrapolate the coefficients. I have a question regarding the 3D corrections in the Airfoil prep. As we provide the Rotor speed(rpm), wind velocity(m/s), the corrections are done only for one angle of attack. However, I want to implement these 3D corrections for all the angle of attacks, the turbine come across during a simulation. So, I have used the 3D correction model available like Snel, Lindenburg, DuSelig and Chavioropoulos & Hansen. At this point, I have doubt whether to add these corrections before BEM or after BEM or during BEM. Any kind of suggestion is highly appreciable.

Regards,
Chaitanya

Jason.Jonkman
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Re: Airfoil Prep - 3D corrections

Postby Jason.Jonkman » Mon Dec 05, 2016 4:48 pm

Dear Chaitanya,

I'm not sure I understand your point about the "single angle of attack", as the 3DStall worksheet of AirfoilPrep applies the Du/Selig correction for Cl and Eggars correction for Cd, across a range of angles of attacks

Regardless, we normally apply the 3D correction before running BEM. I've heard others say that some BEM tools apply the 3D corrections internally, but this is not true of existing NREL-developed tools, which require that the 3D corrections be applied in a pre-processing step. NREL has preferred to apply the 3D corrections in a pre-processing step because the corrections usually require a bit of "finessing" to ensure that the correction is reasonable, which cannot be well automated.

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

Majjari.Chaitanya
Posts: 24
Joined: Wed Apr 20, 2016 4:18 am
Organization: Fraunhoffer Gesellschaft
Location: Germany

Re: Airfoil Prep - 3D corrections

Postby Majjari.Chaitanya » Tue Dec 06, 2016 6:22 am

Respected MR. Jason Jonkman,

Thank you for your reply. I have made the statement "single angle of attack", as I though that the Rotor rpm and the wind speed are used to find the particular angle of attack. At present, I'm working on the implementaion and positioning of the 3D corrections in OneModelica library load simulation tool. If I want to implement these 3D correction models, I need the information of the angle of attack and realtive velocity, which I get after BEM. So, I'm curious to know if it is correct to apply these 3D corrections after BEM. I could not find a source which says the order at which these corrections has to be implemented.
I have found a paper "Valery L. Okulov, Jens N.Sorensen, David H.Wood. (2015). “The rotor theories by Professor Joukowsky: Vortex theories”. In: Progress of Aerospace Sciences, pp. 13. (https://scholar.google.com/scholar?q=Th ... _sdt=0%2C5)", which says 3D corrections has to be implemented before passing the airfoil coefficients to BEM.
I have also found a source "Weinzierl G. A BEM based simulation-tool for wind turbine blades with active flow control elements, 2011, Diploma Thesis.", 3D corrections should not be applied along with BEM.
I have considered the following 3D corrections models for the moment:
1) Snel
2) Lindenburg
3) Du and Selig
4) Charviaropoulus & Hansen
Among the different models I have considered, only Snel can be applied before BEM as it just require the information of chord and radius. All the other models cannot be implemented beofre knowing the outputs from BEM model.
I'm very curious to know, how some BEM tools apply these 3d corrections internally and at what point do they apply them.

Regards,
Chaitanya

Jason.Jonkman
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Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
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Re: Airfoil Prep - 3D corrections

Postby Jason.Jonkman » Tue Dec 06, 2016 7:07 am

Dear Chaitanya,

The rotor speed, radius and wind speed are entered in the 3DStall sheet in order to calculate a (modified) tip-speed ratio, not an angle of attack. I'm not an expert on any of these models, but the Du and Selig model can (and should be) applied before applying BEM.

Perhaps your question is if the correction depends on the tip speed ratio, how can the correction be applied in a pre-processing step if the tip-speed ratio changes throughout a simulation? We at NREL typically use average (or rated) conditions to apply the correction, but one could always perform a sensitivity analysis to determine if the results are strongly dependent on applying the correction at a specific tip-speed ratio and adopt the airfoil data for the specific conditions of the simultation.

I cannot comment on how BEM tools that apply the corrections internally function, as NREL-developed tools don't function this way.

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


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