Xt, yt, zt frame

Dear @Jason.Jonkman,

Hope you are doing well.

—> the frame xt, yt, zt, is the frame located at the tower base right ?
The orientation of xt is always along the wind direction right ? i.e., the direction of xt changes with the yaw of the nacelle right ?

—> In ElastoDyn, RotSpeed is positive means that the rotor turns clockwise i.e. the vector RotSpeed is directed along positive xt axis right ?

—> Also in ElastoDyn, the vector nacelle yaw is directed along positive zt axis right ?

—> If I disable the nacelle yaw degree of freedom, and the nacelle yaw angle is set to 20 degrees. If i want to have a wind which faces the rotor plane, what should i do ? Should i set the HFlowAng to +20 deg ? And could you please clarify, along which axis the vectors HFlowAng and VFlowAng are directed ?

Best Regards,

Here are my responses:

• I agree that xt/yt/zt coordinate system in ElastoDyn is located at the tower base, but this coordinate system is fixed within the base of the tower and does not change with nacelle yaw angle or wind direction. If there is nonzero motion of the tower base through the ElastoDyn platform degrees of freedom, than the tower base coordinate system will no longer be aligned with the global coordinate system.
• I agree that a positive rotor speed means clockwise rotation when looking downwind. This would only be about xt if the platform motion, tower deflection, nacelle yaw angle, and shaft tilt are all zero.
• The nacelle-yaw angle in ElastoDyn is only around positive zt when the tower is not deflected. when the tower is deflected, than the nacelle will yaw around an axis directed along the tower at the tower top.
• InflowWind uses a different convention than ElastoDyn, so, to align the wind direction with a nacelle-yaw angle of +20 degrees, would require that the set the PropagationDir to -20 degrees in InflowWind. Of course, for these to be fully aligned, with the rotor plane, would again require that platform motion, tower deflection, and shaft tilt be zero.

Best regards,

1 Like

Dear @Jason.Jonkman ,

Thank you for your reply ! It is now more clear to me !!!

However, i was wondering what is the difference between PropagationDir in InflowWind and the options HFlowAng and VFlowAng in Turbsim ?

Best Regards,