Dear Nacer,
Here are my answers to your questions:
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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.
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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).
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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: Where to find airfoil data - #3 by Marshall.Buhl. I’m not aware that NREL currently supports a database of publicly available wind turbine airfoils.
Best regards,