Hello!

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 6.3.1.3 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 > 0.5*GridHeight)
125.0 GridHeight - Grid height [m]
125.0 GridWidth - Grid width [m] (should be >= 2*(RotorRadius+ShaftLength))

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.

Yours,