Dear all,

I have a small query regarding the RtAeroPwr variable, and maybe my understanding of Betz’s law.

I have a run the 5MW OC4 case, with a 12mps wind speed, with OF 3.2 and here are my results for the generator power and rotor aerodynamic power :

The mean for this values are 4.19 MW for the generator power and 4.50 MW for the rotor aero power. I don’t understand how the generator can get close to the total available power, as it means it would infringe Betz’law. Or is the rotor aerodynamic power already multiplied by the Betz coefficient ? I did not see a mention of this in the AeroDyn 15 documentation (which I only read briefly).

Best regards,

Maximilien

Dear @Maximilien.Andre,

AeroDyn output `RtAeroPwr`

is the aerodynamic power extracted by the rotor, which already takes into account the Betz limit (and aerodynamic losses relative to the Betz limit such as drag and wake rotation) relative to the aerodynamic power that is available in the wind (0.5*AirDens*SweptArea*V^3). ServoDyn output `GenPwr`

is the electrical power output of the generator, which accounts for other losses between the aerodynamic power and electrical power, e.g., mechanical friction and mechanical-to-electrical conversion efficiency.

Best regards,

Dear Jason,

Thank you for the answer, I have computed the available power with

`df['AvailablePower'] = df['RtArea']*(df["RtVAvgxh"]**2+df["RtVAvgyh"]**2+df["RtVAvgzh"]**2)**(3/2)*rho/2 `

It seems much better like this.

Best,

Maximilien

Dear @Maximilien.Andre,

I’m glad your results make more sense to you know.

Just FYI: For power available, I would look at the wind vector normal to disk rather than the magnitude of the total wind vector at the disk.

Best regards,