Location of pitch axis for airfoil twist in HARP_OPT

Wind & Water Rotor Aerodynamics
1

Hi everybody,

First of thanks to NREL for developing Harp_Opt code.
I modeled a 3 m hydrokinetic turbine rotor and get the twist, and chord distributions.
My questions are that;
Where is the exact location of blade pitch axis in Harp_Opt? (There are different approaches such as 25, 30 or 33 % of chord)

On the other hand, what is the exact meaning of pre-twist angle. Is it the angle between tangential velocity vector(direction of motion) and the airfoil chord line? Or it is the angle between the tangential velocity vector and the relative velocity vector?

Consequently, how can I export the axial and radial induction factors for each blade element , for different free stream velocities in Harp_Opt?

Best Regards.

2

Hello Abdullah,

The blade element momentum theory used by HARP_Opt does not account for the pitch axis. The angle between the chord line and the plane of rotation is known as the pre-twist angle. WT_Perf is included with HARP_Opt, and you can use it to run further analysis on designs produced by HARP_Opt. The induction factors (and many additional variables) are written in the “blade element data” file with the *.bed extension.

Hope this answers your questions.

Kind Regards,
Danny