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Input files for tidal stream turbine case

Posted: Wed Jun 10, 2020 5:06 am
by Callum.Guy
Hi

I'm a PhD student at Edinburgh looking to complete a simple steady simulation of a 1/20th scale tidal turbine with no turbulent inflow (to best represent tank test conditions which were performed with the inclusion of a flow straightner). I have set up an standalone AeroDyn case using downloaded input files from the OpenFAST manual (https://openfast.readthedocs.io/en/mast ... d-appendix) and I have edited them based on the files found at the end of the NREL report "Predicting Cavitation on Marine and Hydrokinetic Turbine Blades with AeroDyn V15.04" (https://www.nrel.gov/docs/fy17osti/68398.pdf). However, I am getting a quite considerable under prediction of Cp and Ct (see attached images). I would be grateful if anyone with experience of using AeroDyn for a tidal application could offer some advice on any parameters that are particularly sensative or potentially offer some example case files. Any help would be really appreciated.

Cheers
Callum

Just a little extra info on my modelling method:

1) Calculate local Reynolds numbers at each blade station
2) Use XFOIL to obtain Cl/Cd data for each Reynolds number (0.01 ~ 0.15 [E+6])
3) Extrapolate Cl/Cd tables using AirfoilPrep
4) Input required data into AeroDyn Case files
5) Simulate

Re: Input files for tidal stream turbine case

Posted: Wed Jun 10, 2020 4:19 pm
by Jason.Jonkman
Hi Callum,

I'm not an expert on tidal stream turbine analysis, but the accuracy of AeroDyn's BEM method is tied to the accuracy of the airfoil data input. Your approach to obtaining the airfoil data sounds OK, but there could be inaccuracies, e.g., due to the 3D and/or rotational augmentation effects. Does using the rotational augmentation correction to the airfoil data built within AirfoilPrep result in improved prediction of Cp and Ct?

Best regards,

Re: Input files for tidal stream turbine case

Posted: Thu Jun 11, 2020 4:50 am
by Callum.Guy
Hi Jason,

thanks for getting back to me. In answer to your question no I haven't converted my Cl/Cd table into the 3D version, I assume this is done with the 3DStall sheet? The issue I'm having is that I have 23 blade stations and 7 TSRs to simulate. Within the 3DStall sheet you specify r/R and RPM so I would need to generate 161 seperate tables. I have tried to use the python script for automation but I am running into issues as described here:

https://github.com/WISDEM/AirfoilPreppy/issues/18

Any advice would be appreciated.

Cheers
Callum

Re: Input files for tidal stream turbine case

Posted: Thu Jun 11, 2020 6:37 am
by Jason.Jonkman
Dear Callum,

Regarding AirfoilPreppy, I'm familiar with it, but I do not have any hands-on experience using it. Hopefully Andrew Ning (the developer of AirfoilPreppy) can address your issue on github.

Yes, I was referring to the 3DStall sheet. Before running 161 times, you could first simplify the problem to see how sensitive the effect is. I would typically use the rated TSR (perhaps TSR = 4 for your rotor) and simplify to only using a few (say 5) unique airfoil data tables. If the results are sensitive to the 3D corrections, you could then further refine the solution with more airfoil tables.

Best regards,