# pitching the blade in the negative direction

I have read the 5mw NREL manual and I wanted to know what will happen if I start pitching my blade in the negative direction by 1.5 to 2 degree with wind speed at region 1. I want to know to know if it is possible to do so or the results i might be getting will not be accurate?D oes the model work with a negative pitch angle or not?
thank you
mostafa haggag

Dear Mostafa,

I’m not sure why you’d want to, but you can certainly pitch the blades negative and get “reasonable” results out of FAST. By Region 1 do you mean less than the cut-in wind speed (of 3 m/s for the NREL 5-MW wind turbine)? Very little phenomena happens at such low wind speeds.

Best regards,

I am using wind speed 8m/s steady laminar flow. I am doing a sinusoidal motion with the pitch.I am doing 1.5 degrees in the positive direction and 1.5 degrees in the negative direction. The problem is that the blade start rotating in the opposite direction for a very small amount of time then start moving in the positive direction i was wondering if such thing is even possible or not
thanks

Dear Mostafa,

Are you modeling a condition with the rotor idling with no generator torque?

Best regards,

I am doing this with a 5MW turbine offshore. I am using test20 offshore case made by NREL example files while closing hydro module as i am not checking on it .I am doing this in laminar flow with speed 8m/s
I am testing the loads and the power affects when we start to do a sinusoidal motion on the blade. The problem is as I am pitching the blade in the negative and the in positive( one and a half degree in the positive and one and a half degree in the negatives direction ), the rotor starts to rotate in the opposite direction and then start to go back soi was wondering if this results true? could due to my pitching in the negative leads my blade to rotate in the opposite direction?
in this picture, you can see the red graph is the pitch angle viruses the time and the blue graph is the rotor speed versus the time. The period of the pitch sin wave is 45 seconds.
for lower periods and lower amplitudes, this is not happening.
i was wondering what i may be doing wroungly ?
thanks yu

Dear Mostafa,

My guess is that the generator torque is impacting the behavior of the rotor speed in your case. Again I ask, is the generator torque zero for this case or something else?

Best regards,

the pitch controller is controlled using Simulink and the generator torque control is controlled by the dll fast controller the one I set VSContrl to 5 .
I have attached a graph for generator torque vs time in blue and rotor speed versus time in orange.
i was wondering if such thing could be really happening in real life or not.
the sinusoidal function i am doing is on the 3 blades in phase with each other

Dear Mostafa,

I don’t think the torque-speed curve for the NREL 5-MW turbine was designed to handle negative speeds, so, I wouldn’t use this result. But I’m not sure I know enough about why you are running this simulation to recommend something specific.

Best regards,