# Steady state response of the NREL 5 MW wind turbine rotor under uniform wind conditions

Dear all,

First of all, thank you very much for the opportunity to be a member of this forum.

I want to calculate the steady state response of the rotor of the NREL 5 MW wind turbine under steady and uniform wind conditions (almost the same as that performed for the land-based turbine in nrel.gov/docs/fy09osti/38060.pdf except that I neglect the tower and nacelle effect) using the standalone AeroDyn software based on BEM method. In this regard, I have used the data available in the just mentioned PDF in order to validate my results, including the thrust, torque and power coefficients (although a small difference between the results is expected as I am ignoring the tower and nacelle effects, together with the structural deflections).

Accordingly, I have the following two questions, which I would be so grateful if someone could answer:

1. Is it possible to calculate the steady rotor rotational speed through performing a steady state simulation of an initially stationary rotor where a uniform wind is blown upon it? If yes, what changes are needed to be done in the input/driver files?

2. To perform an initial validation of my results, I have used the normalized values of RotThrust, RotPwr and RotTorq given in the above-mentioned PDF. However, I have noticed that the normalization of the RotThrust using the maximum thrust force available in the wind (1/2air densitywind speed^2rotor sweep area) results in the thrust coefficient values larger than one for wind speeds smaller than roughly 7 m/s (you can see the normalized values in the excel file attached). Could you please check if I am using a correct equation (1/2air densitywind speed^2rotor sweep area) for the normalization of the thrust force or there is something that I am not taking into account?
Thrust.xlsx (11.7 KB)

Dear Mojtaba,

Here are my answers to your questions:

1. Standalone AeroDyn does not have the ability to calculate steady-state rotational speeds for a given fixed wind speed and generator torque. Such an analysis, however, can be done in FAST / OpenFAST.
2. Your equation for Ct looks reasonable, assuming that there is no skewed inflow (from e.g. shaft tilt or yaw error, which would reduce the wind passing through the rotor) and no rotor precone (which would reduce the rotor swept area). Regardless, it is possible for the thrust coefficient to exceed unity in certain situations.

Best regards,

Jason,

Thank you for your response.

Respectfully,
Mojtaba.