# Is positive Yaw error clockwise?

Hi

It seems like the industrial standard approach to yaw misalignment is that if the wind is approaching your turbine from a slightly clockwise direction (when viewed from above) to where your turbine is facing then you have a positive yaw error. To correct the error, you would yaw clockwise, in a positive direction.

Sadly this doesn’t tie up with maths, which likes anti clockwise to be positive. I guess following the industrial standard, positive yaw moments would cause negative movements. I’ve had a quick rummage through the FAST manual, and it doesn’t explicitly say which approach is followed (maths vs industrial standard).

Please could you let me know which way is positive when yawing and would you consider adding a top down view of a turbine to the manual in the section where the coordinate systems are described?

Thanks

Alec

Dear Alec,

In FAST, the wind direction output (HorWndDir), nacelle yaw angle input/ouput (NacYaw) and nacelle yaw error output (NacYawErr) are all defined counter-clockwise when looking from above (this is a positive rotation about the z-axis, which points vertically upwards). In AeroDyn, the wind direction input (WindDir) is defined clockwise when looking from above (which is opposite to that of FAST). For example, in Test01 from the FAST CertTest, NacYaw = -15 degrees and WindDir = -HorWindDir = 30 degrees, which equals NacYawErr = -15 degrees.

I hope that helps.

Best regards,

Thanks Jason, yes it does.
Alec

Hi everyone,

I just want to make sure that I understood the explanation concerning FAST’s yaw convention right.
Would you be so kind to confirm that the picture I created is correct?
It’s supposed to show the turbine viewed from above. The black arrows point out the rotation direction of the blades.

Thanks – and kind regards,
Julia

Dear Julia,

Yes, your image is correct.

Best regards,

Dear Jason,

thanks a lot for the quick response!

Best regards,
Julia

RE: FASTV8.16
Are any of the yaw options possible with the newest versions of FAST?
Mark C

Dear Mark,

What yaw options are you referring to?

Regardless, the yaw functionality is virtually unchanged between FAST v8.16 and earlier versions.

Best regards,

forgot to look under elastodyn inputs. thanks. M