TurbSim User's Guide: Version 1.06.00 - NREL

Figure 9. Default jet wind speed for URef calculation:error bars indicate the range of random variate, N;dotted lines mark the tenth and ninetieth percentilesFigure 10. Default jet height, ZJetMax,without random variates (the randomvariation range is approximately ±50 m)ZJetMax: Height of the Jet [m]The ZJetMax parameter is the height in meters of the low-level jet. Enter the approximate heightat which the low-level jet wind profile reaches its maximum wind speed, or enter the string“default” to have TurbSim calculate a jet height. The default height is a function of parametersRICH_NO and Ustar with a random component based on LLLJP measurements. The defaultheight—without the random component—is plotted in Figure 10. ZJetMax, which must be avalue between 70 m and 490 m, is used to calculate the mean wind speed and direction profiles.It is used only when WindProfileType is “JET.”PLExp: Power-Law Exponent [-]The PLExp parameter is used to compute the mean u-component wind speeds across the rotordisk when WindProfileType is “IEC” or “PL.” It is the exponent used to define the power-lawwind profile,( )u zPLExp⎛ z ⎞= uhub⎜ ⎟⎝HubHt⎠, (9)where z is the height above ground level. The exponent can be positive, negative, or zero (for noshear). Enter the string “default” to have TurbSim use a default value based on the specifiedspectral model, as shown in Table 7. If KHTEST is specified for parameter IECturbc, the PLExpparameter is overwritten to 0.3.Z0: Surface Roughness Length [m]The surface roughness length, Z0, is the last parameter in this section. This length—a measure ofthe roughness of the surface terrain—is the extrapolated height at which the mean wind speedbecomes zero in a neutral atmosphere, assuming a logarithmic vertical wind profile:( )u zz( Z0 )RefHt( Z0 )ln= URef . (10)ln16