rotor speed in FAST

I’m trying to run the 5 MW wind turbine at constant rotor speed. I’ve turned off the active pitch control and assigned a constant collective pitch. I’ve also turned off the variable speed control. I’m using a constant wind. I’ve also tried changing the generator model to the simple one (option 0). However, it seems that my rotor speed is still increasing over the course of the 2 minute run. What am I missing?

Dear Chris,

In FAST, the rotor will accelerate or deccelerate if the aerodynamic torque doesn’t balance the reaction torque from the generator/drivetrain. If you wish to have constant rotor seed regardless of this torque balance, simply disable the generator DOF by setting GenDOF to False in FAST’s primary input file.

I hope that helps.

Best regards,