I’m working on the IEA 15 MW RWT to develop my MSc thesis.
At the moment I’m trying to validate the results I obtained with BEMT with a higher fidelity method (OLAF).
For this reason I am currently trying tosimulate the wind turbine with fixed foundations. The wind turbine is modelled as rigid. SubDyn, HydrDyn, ServoDyn and MoorDyn modules are not activated. The wind is uniform and steady, with constant rated value (10.59 m/s).
My concern arises since the RtAeroPwrs that I obtain with OLAF and BEMT differ significantly. In particular, the RtAeroPwr for OLAF is also way higher than rated power.
For OLAF input file, initially I tried following the recommendations on the OpenFAST online documentation. After that I tried modifying the DeltaPsi parameter (suggested as 6° in the documentation) and all the parameters which, according to the documentation, can be defined from it (i.e. DTfvw, nNWPanel, WakeLength, FreeWakeLength). I could not achieve a result closer to BEMT anyway.
Afterwards I tried modifying nNWPanels, FreeWakeLength and WakeLenght parameters, leaving DTfvw untouched: the idea is to increase the near wake region. I could reach steady values closer to BEMT one, but still with more than 8% difference.
I’m attaching a plot where different simulations are compared over time (with Power on the y-axis). It shows BEMT compared with many different OLAF simulations (differences in setting are written in the legend). The recommended values would be nNWPanel=120; FreeWakeLenght=180; WakeLength=600, and are the ones leading to the red dotted line (the farthest from BEMT value).
I was wondering if you knew why the results are so different – or if you could advise on how to achieve a better match.
Thank you very much,