# Direction of the incoming wind

Hello every body,

I am modeling an upwind turbine, with zero yaw angle. Wind is blowing to the rotor such that it makes a 90 degree angle with the rotor plane.
In the hub-height wind file for AeroDyn the third column is related to the direction of the horizontal wind, Based on the AeroDyn user’s guide I concluded that in my turbine’s condition, this angle must be set to 180 degrees.

Best Regards
Sara

Dear Sara,

The x-axis of the inertia frame in FAST (the xi-axis) is the nominal (zero-degree) wind direction for both upwind and downwind rotors. For upwind rotors with zero yaw angle, the xi-axis is directed from the rotor to the tower; vice-versa for downwind rotors.

If you don’t want any yaw error, set both the wind direction and yaw angle to zero degrees (both for upwind and downwind rotors).

If the wind direction is 180 degrees, and the yaw angle is zero, than the yaw error will be 180 degrees.

I hope that clarifies things.

Best regards,

Dear Jason,

I set the wind direction equal to zero and I got “NAN” for CLift,CDrag, and the aerodynamic forces (read from the AeroDyn output file), I did not have this problem when I had set the wind direction equal to 180 degrees. I appreciate it if you could help me find out what the problem is.

Best Regards
Sara

Dear Sara,

I’m sorry, but I don’t know what is causing the problem. You are going to have to play around with the model input settings to identify the problem. Here are a few questions to help with the debugging process:

*Do your airfoil tables cover the complete 360 degrees of angle of attack (-180 to 180 degrees)?
*Have you tried running a simulation without dynamic stall enabled (StallMod = STEADY)?
*Do you get other errors or warnings when running the simulation, e.g., a warning regarding a small angle assumption violation?

Best regards,