Aerodyn gives an error message when I specify a wind direction (DELTA) of 180 deg (it cannot determine the wind direction in that case). The simulation runs fine with DELTA=179 deg.
Now I know that for turbulent (FF) wind files it is recommended to simulate yaw errors by means of specifying yaw angles rather than wind directions (HFlowAng). Must I also do that for HH-wind files or can I safely use yaw angle=0 and wind dir = DELTA = 179 deg?
You can safely specify the wind direction to be nonzero within AeroDyn’s hub-height wind files.
In the current version of AeroDyn, we suggest setting the wind direction of turbulent wind files to zero because the “planes” used to define the turbulent wind are assumed to translate along the positive x-axis of the inertia frame, regardless of the wind direction. However, it is on our development to-do list to add an option for the user to specify the wind direction of turbulent wind files. We plan to add this feature to FAST v8 later this summer.
I have never tried to run with a 180-deg wind direction in the HH files, so it could be that there’s a problem with it. I wonder if 540 degrees would work. Otherwise, I suggest trying 179.99. Either that, or yaw the turbine 180 and use a 0-deg wind direction like you would do with FF files. My guess is that this is an issue only for exactly 180-deg wind direction.