Blade Element Method

[Nacer.Boumezbeur]

Hi Sir
i am working with my BEM matlab Code , and i have to be sure about three points before going further:

1. I noticed that always the relative velocity over the radius of the blade is linear. is it always the case?
2. for blade optimization the optimun value of axial induction factor is 1/3 , is there any optimal value for tangiential induction factor?
3. i am looking for big data base for all airfoils aoa vs cl,cd , if you can recommand me the best .

thank you

[Jason.Jonkman]

Dear Nacer,

Here are my answers to your questions:

1) The relative velocity may be dominated by the rotor rotation, omega x r, which is linear with radius (r), but there are other factors that can impact the relative velocity, including shear, yaw, turbulence, turbine vibrations, etc.

2) An axial induction of 1/3 is Betz optimal for ideal conditions. The tangential induction is associated with wake rotation, and the ideal (from Betz theory) would be 0. For a high TSR rotor, I would expect small values of the tangential induction (close to zero).

3) The following forum post from many years ago has links to several publicly available airfoil data tables, but some of the links are broken nowadays: viewtopic.php?f=7&t=856&p=4262. I'm not aware that NREL currently supports a database of publicly available wind turbine airfoils.

Best regards,