problem about the turbulence intensity of the wind


To test a model of the wind turbine, I need to generate wind with different conditions.

The turbulence intensity of the wind depends on the wind speed (according to Normal Turbulence Model, IEC 61400-1 ed3). For example for 10 m/s it should be 7.875. So I generated the wind with using the following TurbSim input file:


[code]---------Runtime Options-----------------------------------
516423515 RandSeed1 - First random seed (-2147483648 to 2147483647)
RanLux RandSeed2 - Second random seed (-2147483648 to 2147483647) for intrinsic pRNG, or an alternative pRNG: “RanLux” or “RNSNLW”
False WrBHHTP - Output hub-height turbulence parameters in binary form? (Generates RootName.bin)
False WrFHHTP - Output hub-height turbulence parameters in formatted form? (Generates RootName.dat)
False WrADHH - Output hub-height time-series data in AeroDyn form? (Generates RootName.hh)
True WrADFF - Output full-field time-series data in TurbSim/AeroDyn form? (Generates RootName.bts)
False WrBLFF - Output full-field time-series data in BLADED/AeroDyn form? (Generates RootName.wnd)
True WrADTWR - Output tower time-series data? (Generates RootName.twr)
False WrFMTFF - Output full-field time-series data in formatted (readable) form? (Generates RootName.u, RootName.v, RootName.w)
False WrACT - Output coherent turbulence time steps in AeroDyn form? (Generates RootName.cts)
True Clockwise - Clockwise rotation looking downwind? (used only for full-field binary files - not necessary for AeroDyn)
0 ScaleIEC - Scale IEC turbulence models to exact target standard deviation? [0=no additional scaling; 1=use hub scale uniformly; 2=use individual scales]

--------Turbine/Model Specifications-----------------------
35 NumGrid_Z - Vertical grid-point matrix dimension
35 NumGrid_Y - Horizontal grid-point matrix dimension
0.05 TimeStep - Time step [seconds]
650.0 AnalysisTime - Length of analysis time series [seconds]
650.0 UsableTime - Usable length of output time series [seconds] (program will add GridWidth/MeanHHWS seconds) [bjj: was 630]
80.03 HubHt - Hub height [m] (should be > 0.5GridHeight)
125.0 GridHeight - Grid height [m]
125.0 GridWidth - Grid width [m] (should be >= 2
0 VFlowAng - Vertical mean flow (uptilt) angle [degrees]
0 HFlowAng - Horizontal mean flow (skew) angle [degrees]

--------Meteorological Boundary Conditions-------------------
IECKAI TurbModel - Turbulence model (“IECKAI”=Kaimal, “IECVKM”=von Karman, “GP_LLJ”, “NWTCUP”, “SMOOTH”, “WF_UPW”, “WF_07D”, “WF_14D”, or “NONE”)
“3” IECstandard - Number of IEC 61400-x standard (x=1,2, or 3 with optional 61400-1 edition number (i.e. “1-Ed2”) )
7.8750 IECturbc - IEC turbulence characteristic (“A”, “B”, “C” or the turbulence intensity in percent) (“KHTEST” option with NWTCUP, not used for other models)
NTM IEC_WindType - IEC turbulence type (“NTM”=normal, “xETM”=extreme turbulence, “xEWM1”=extreme 1-year wind, “xEWM50”=extreme 50-year wind, where x=wind turbine class 1, 2, or 3)
default ETMc - IEC Extreme turbulence model “c” parameter [m/s]
PL WindProfileType - Wind profile type (“JET”=Low-level jet,“LOG”=Logarithmic,“PL”=Power law, or “default”, or “USR”=User-defined)
80.03 RefHt - Height of the reference wind speed [m]
10 URef - Mean (total) wind speed at the reference height [m/s]
default ZJetMax - Jet height [m] (used only for JET wind profile, valid 70-490 m)
0.14 PLExp - Power law exponent [-] (or “default”)
default Z0 - Surface roughness length [m] (or “default”)

--------Non-IEC Meteorological Boundary Conditions------------
default Latitude - Site latitude [degrees] (or “default”)
0.05 RICH_NO - Gradient Richardson number
default UStar - Friction or shear velocity [m/s] (or “default”)
default ZI - Mixing layer depth [m] (or “default”)
default PC_UW - Hub mean u’w’ Reynolds stress [(m/s)^2] (or “default”)
default PC_UV - Hub mean u’v’ Reynolds stress [(m/s)^2] (or “default”)
default PC_VW - Hub mean v’w’ Reynolds stress [(m/s)^2] (or “default”)
default IncDec1 - u-component coherence parameters (e.g. “10.0 0.3e-3” in quotes) (or “default”)
default IncDec2 - v-component coherence parameters (e.g. “10.0 0.3e-3” in quotes) (or “default”)
default IncDec3 - w-component coherence parameters (e.g. “10.0 0.3e-3” in quotes) (or “default”)
default CohExp - Coherence exponent (or “default”)[/code]

I used 650s for the generation, and I want to use 600s for the evaluation (50s as the transient). However after the simulation is done, the calculated intensity becomes 7.2911 instead of 7.875 (using 600 seconds - also 7.203 using 650 seconds).
How can I fix this problem?

Thank you so much for your time in advance.


Dear Iman,

The numerical implementation of TurbSim will not yield results that have the exact TI specified, unless the ScaleIEC switch in the input file is set to 1 or 2. See the description of input ScaleIEC in the TurbSim User’s Guide for more information:

Best regards,