Yes Jason, i meant “phi” not ‘x’.
My main concern is how to deal with the case of a=1, and a’ = -1; I understand your comments on Vx, Vy. Since I’m looking at the simple case of rigid blades, I’m using V_wind and r*Omega instead of Vx, Vy.
Could you please tell me how are these exceptional cases resolved in AeroDyn or FAST?
My understanding is that for a=1, the residual equation used is: - cos(phi) * (Vx/Vy) * (1 - k_prime) not equation22.
But I can’t understand how is the a’ = -1 dealt. Thanks.
Regards,
Kumara
Dear Kumara,
AeroDyn uses 1/(1+a’) = (1-k’), which is equivalent based on Equation (21) in our AIAA SciTech 2015 paper linked above. Likewise, AeroDyn uses 1/(1-a) = (1-k), which is equivalent based on Equation (20).
Please note that if a’=-1, then phi = +/-90 degrees, based on the sign of Vx (see Figure 2). And if a=1, then phi = 0 or 180 based on the sign of Vy. If both a=1 and a’=-1, then phi is undefined, but irrelevant because the dynamic pressure and aerodynamic loads are zero anyway (Equations (23)-(27)).
Best regards,