Power Coefficient

Wind & Water Controls
1

Dear Dr. Jonkman,
In wind turbines, is it possible that CP (Power Coefficient) becomes negative sometimes in region 3?
Thanks,
Best regards,
Sina

2

Dear Sina,

I would normally except the time-averaged value of Cp to remain positive in Region 3, but I could imagine situations where the instantaneous value of Cp goes negative temporarily.

Best regards,

3

Dear Dr. Jonkman,

Thanks for your prompt response. In what situations CP is negative? For instance, is it possible when we have a sudden drop in the wind speed creating a negative torque and finally a negative power coefficient, i.e the wind turbine behaves like a motor (propeller)?

Thanks,
Best regards,
Sina

4

Dear Sina,

I’m not sure, but the instantaneous values of Cp certain fluctuate when simulating in turbulence. Again, I wouldn’t look at that much, focusing instead on the time-averaged Cp values.

Best regards,