Dear Jian.Zhang,

TurbSim uses the equation

sigma_1=I_ref*(0.75*V_hub+5.6)

that you mention (where I_ref is based on turbulence class A, B, or C), but it does not use the equation

sigma_1=V_hub/ln(Z_hub/Z_0)+1.28*1.44*I_15.

The first equation is dictated by the chosen wind turbine class, as implemented in TurbSim, but the second equation can be used for the assessment of ambient turbulence in the absence of specific measurements, which is not really a functionality of TurbSim.

When a turbulence intensity is specified in TurbSim, I agree with your equation

sigma_1=IECturbc*u_hub/100,

but IECturbc = “A” and IECturbc = 16 are only equivalent when

0.16*(0.75*V_hub+5.6) = 0.16*V_hub,

i.e., at V_hub = 22.4 m/s.

We’ve used TurbSim to model non-neutral atmospheric flows (e.g., in the paper you reference by Doubrawa et al) by specifying the desired turbulence characteristics like the profile (shear, veer), turbulence spectra (in u, v, w), spatial coherence, and Reynold’s stresses in place of the default IEC model. The second paper you reference by Wang et al is again applicable to the assessment of ambient turbulence in the absence of specific measurements, which again is not really a functionality of TurbSim. NREL is not currently funded to implement other turbulence models in TurbSim.

Best regards,