Rotor tilt provided at runtime

[misi9170]

This discussion is concerned with whether we should allow users to provide turbine tilt angles at runtime (for example, in the calculate_wake method of FlorisInterface) in a manner similar to how yaw angles are provided, or whether tilt angles should be part of the turbine definition only (the status quo).

Generally speaking, turbine tilt angles are not controllable in the way that yaw angles are, and the current implementation of rotor tilt allows (uncontrollable) specification of the tilt angle in the turbine yaml using:

• ref_tilt_cp_ct (presumably, the design tilt angle of the turbine rotor)
• floating_tilt_table (for floating turbines, specifies the tilt angle at different wind speeds)

However, there may be users who would like to quickly vary the tilt angles external to the turbine definition file. Allowing methods on FlorisInterface to accept tilt angles in a manner similar to yaw angles would provide this. Code to do part of this job is already in place in calculate_wake(), but has been commented out (#651) because it is not complete. This code would need to be propagated to other methods on FlorisInterface if we decide to move forward with allowing tilt angles to be specified at runtime.

If we decide to allow users to specify tilt angles at run time, we will need to decide how to reconcile the provided tilt angle with the value provided from the floating_tilt_table, if the turbine is floating. Presumably, the provided tilt angle should override the value from the floating tilt table, but this would need to be implemented and verified. Further, we would need to decide whether a user-provided tilt angle is taken as a delta from ref_tilt_cp_ct or as an absolute value---this was not an issue for the yaw angle, as we implicitly assumed that the reference yaw angle is 0 (or at least, 0 mean).

[misi9170]

@bayc @paulf81 Hoping to get your thoughts here when you have the time. If we decide to provide this sort of functionality, it would be after the imminent release.