we use the NREL 5 MW reference turbine data for our turbine parameterizations in an LES code.
We have complex parameterizations like actuator line model and enhanced actuator disk model (similiar calculations as in actuator line model, however not for discrete blade lines but for each point across the rotor disk). In these models we consider the 5° shaft tilt. But we also have a standard actuator disk model. Here, we specify a thrust curve (see attachment) which is based on Fig. 9-1 in the report or rather the thrust values given in this topic: NREL 5-MW reference turbine. C_T is calculated as: C_T = 2*thrust / ( rho * pi * r^2 * u^2 ) with rho = 1.225 kg/m3, r = 63 m, thrust and u the corresponding values from Fig. 9-1.
In the current code, the C_T values > 1 are set to 0.9999 to enable a calculation of the axial induction factor for determining the reference velocity. In the future we plan to include a Glauert correction.
I have some questions:
Can you confirm these C_T values, are they reasonable and do you have similar values? And could you provide a more detailed table - for example I added values determined by eye from the graphic curve in the region where C_T drops very fast (11.3 and 11.7 m/s), with a linear interpolation between 11 and 12 m/s we would make a significant error.
Do we have to account for the shaft tilt of 5° when we want the thrust to act on the mean flow? In other words: Do we need a tilt correction (which we apply in the actuator line model) - or is this already included in the thrust curve of Fig. 9-1?
When we include the Glauert correction, this is only valid for C_T < 2 (although even with values near 2, the axial induction factor approaches 1 and the thrust would go to infinity) - so what to do with the C_T > 2 for u < 3.7 m/s?
NREL_5MW_C_T_new.txt (276 Bytes)