TurbSim User's Guide: Version 1.06.00 - NREL

⎛1000⎞θ = T ⎜ ⎟⎝ p ⎠0.286. (12)The RICH_NO parameter is used to calculate the velocity spectra and the JET and LOG windprofiles, scale coherent structures, and determine default values for many input parameters.Enter zero for neutral conditions, a negative value for unstable conditions, or a positive numberfor stable atmospheric conditions. The GP_LLJ and NWTCUP models limit this input to−1 ≤ RICH _ NO ≤ 1. If KHTEST is specified for parameter IECturbc, the RICH_NO parameteris overwritten to 0.02. The RICH_NO parameter does not accept the value “default.” TheRICH_NO parameter is not used for the TIDAL spectral model.UStar: Rotor-Disk Average Friction Velocity [m/s]The parameter UStar is the friction or shear velocity, u*, averaged over the rotor disk:UStar = u*= ∑ uw ' ' ,1npnpi=1i(13)where the prime quantities indicate the fluctuating (zero-mean) longitudinal (u) and vertical (w)wind components at n p measurement points on the rotor disk. The GP_LLJ model, which scalesthe velocity spectra with local friction velocities ( u *values varying with height), assumes thatUStar is the average friction velocity of three points on the u*profile: one at the hub, one at thetop of the rotor, and one at the bottom of the rotor.UStar is used to scale the velocity spectra of non-IEC spectral models, to scale the JET and H2Lmean velocity profiles, and to calculate the default values of many input parameters. Enter UStarin units of meters per second or enter “default” to have TurbSim calculate an appropriate value.The default value for the TIDAL model is UStar = 0.05 URef. For non-hydro spectral models(i.e., all but TIDAL), the default value is calculated using the diabatic u*0(near the surface),which is predicted by Panofsky and Dutton’s modified logarithmic profile [24] usingu*0=ln0.4URefRefHt( ) −Ψ ( _0MRICH NOZ), (14)where ΨMis a function that depends on the RICH_NO stability parameter. The relationshipbetween RICH_NO and u*0, normalized by URef, at RefHt = 80 m is plotted in Figure 11. Therelationship between u*0and the default Ustar is shown in Figure 12.If “default” is entered for the reference wind speed, Uref, the string “default” cannot be enteredfor the UStar parameter, because the default values for the two parameters are interdependent.18