Hello everyone, I’d like to share an observation that could be interesting for others as well.
I used FAST.Farm to determine the wake trajectory of a 5 MW NREL turbine with 30 deg. yaw (8 m/s wind & TI= 10 % via Turbsim), as seen in the first figure below (wake deflection vs downstream distance). Since the flow is turbulent, I averaged 1 hour simulation data, which started after a 20 min ramp-up period (for the initial wake development).
To make sure that 20 min is enough (or too much), I prepared the second figure below. In the 2nd figure, every point is an average of 1 h data, starting at different points of time. It seems like 15 min of ramp-up time would be needed, in order to get a fully developed wake, before one starts to evaluate statistics.
As a final note, when I increased the input value of f_c (cutoff frequency of the low-pass time-filter, default = 0.0007) the required ramp-up time decreases drastically. 3 or 4 min ramp-up would be sufficient, with f_c = 0.07 or 0.007, respectively. The time-averaged wake position and its standard deviation are affected very little (probably negligible).
Regards,
