about OLAF

[robytian]

Dear all, In addition to BEM theory, there are other methods to calculate the aerodynamic load of wind turbines. Dr. David used his lift line free vortex wake method to model the blades and directly calculated the aerodynamic load of wind turbines from the perspective of vorticity. The OLAF module in FAST uses the method of combining BEM with vortex . Can Dr. David's method and the method of combining OLAF module with BEM currently used in FAST be used for floating wind turbine calculation?

[ebranlard]

Dear @robytian

OLAF uses a vorticity-based lifting-line approach and it is distinct from BEM. There are however different ways to solve for the circulation on the lifting-line, and OLAF currently uses a polar-based approach, which is generally more accurate than solving for the circulation with a no-flow-through approach due to the wide range of polars and angle of attacks used by wind turbines. I'm not familiar with the method of David, but it sounds similar to what OLAF uses, maybe it uses a different method to solve for the circulation? Maybe you can attach link/references for the method you are mentioning?

You may also look at the theory of OLAF here: https://openfast.readthedocs.io/en/dev/source/user/aerodyn-olaf/OLAFTheory.html

I hope that helps,

Emmanuel

[robytian]

Dear ebranlard： I forgot to reply to you，David Marten is the founder of the Qblade software and uses the same method which is a combination of lift lines and free vortex wake, but I think there are some small differences with OLAF, although both are Lagrangian vortex methods, there are some differences in the processing steps of the vortex elements and the calculation methods of the wake field. Here is his PhD thesis and the qblade theory manual. https://www.researchgate.net/publication/344901299_QBlade_A_Modern_Tool_for_the_Aeroelastic_Simulation_of_Wind_Turbines https://docs.qblade.org/src/theory/aerodynamics/lifting_line/lifting_line.html

Also, I would like to ask if the OLAF module can be used as a aerodynamic calculation in the floating turbine example? Since I see that the OLAF module is currently in a separate case folder, if I want to replace the BEM in Aerodyn15 in OC4 with OLAF, how should I do it?

[ebranlard]

Dear @robytian Thank for your reply and clarifying, who Dr David was :) I probably don't have the time to dive into the thesis but I am definitely curious about what the differences in implementation can be.

OLAF can definitely be used for offshore simulations. As you mentioned, it's mostly a matter of switching WakeMod from 1 or 2 to 3, and setting up an OLAF input file.

You can have a look at the following resources to help setup your OLAF input file:

• OLAF guidelines
• Some discussions in this thread

[robytian]

Dear ebranlard

Hi，I want to develop the lift line method and the bound circulation solving algorithm based on lift coefficient separately. Where are the codes of these two parts? In other words, I want to model the blade as a lift line, and then solve and update the bound vortex circulation by Garrel's method. Which part of the source code given by FAST should I refer to?

Best regards，

[ebranlard]

Dear @robytian, You'll find the polar-based lifting line algorithm here: https://github.com/OpenFAST/openfast/blob/dev/modules/aerodyn/src/FVW_Wings.f90#L308

with some documentation here: https://openfast.readthedocs.io/en/dev/source/user/aerodyn-olaf/OLAFTheory.html#lifting-line-representation

Let me know if you have any questions,

Emmanuel