PSD of the IECKAI model

Hello everyone,

I am trying to verify the Power Spectral Density of the Kaimal Spectrum given in TurbSim 2.0. I have ran 7 different simulations, each having a simulation time of 18 hours and a time step of 0.1 seconds. I assume that there is no coherence and am only interested in the background turbulence. An example of the input file is provided below:

---------TurbSim v2.* Input File------------------------
Example file that can be used with simulations for the NREL 5MW Baseline Turbine; note that UsableTime has been decreased in this file so that the file distributed with the FAST CertTest isn’t as large
---------Runtime Options-----------------------------------
False Echo - Echo input data to .ech (flag)
13428 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”
True WrBHHTP - Output hub-height turbulence parameters in binary form? (Generates RootName.bin)
True 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)
False WrADTWR - Output tower time-series data? (Generates RootName.twr)
False WrHAWCFF - Output full-field time-series data in HAWC form? (Generates RootName-u.bin, RootName-v.bin, RootName-w.bin, RootName.hawc)
True 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)
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-----------------------
41 NumGrid_Z - Vertical grid-point matrix dimension
41 NumGrid_Y - Horizontal grid-point matrix dimension
0.1 TimeStep - Time step [seconds]
64800 AnalysisTime - Length of analysis time series [seconds] (program will add time if necessary: AnalysisTime = MAX(AnalysisTime, UsableTime+GridWidth/MeanHHWS) )
ALL UsableTime - Usable length of output time series [seconds] (program will add GridWidth/MeanHHWS seconds unless UsableTime is “ALL”)
90 HubHt - Hub height [m] (should be > 0.5GridHeight)
170 GridHeight - Grid height [m]
170 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”,“IECVKM”,“GP_LLJ”,“NWTCUP”,“SMOOTH”,“WF_UPW”,“WF_07D”,“WF_14D”,“TIDAL”,“API”,“USRINP”,“TIMESR”, or “NONE”)
“TurbSim_User.spectra” UserFile - Name of the file that contains inputs for user-defined spectra or time series inputs (used only for “USRINP” and “TIMESR” models)
“1-ed3” IECstandard - Number of IEC 61400-x standard (x=1,2, or 3 with optional 61400-1 edition number (i.e. “1-Ed2”) )
“B” IECturbc - IEC turbulence characteristic (“A”, “B”, “C” or the turbulence intensity in percent) (“KHTEST” option with NWTCUP model, 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 - Velocity profile type (“LOG”;“PL”=power law;“JET”;“H2L”=Log law for TIDAL model;“API”;“USR”;“TS”;“IEC”=PL on rotor disk, LOG elsewhere; or “default”)
“TurbSim_User.profiles” ProfileFile - Name of the file that contains input profiles for WindProfileType=“USR” and/or TurbModel=“USRVKM” [-]
90 RefHt - Height of the reference velocity (URef) [m]
14 URef - Mean (total) velocity at the reference height [m/s] (or “default” for JET velocity profile) [must be 1-hr mean for API model; otherwise is the mean over AnalysisTime seconds]
“default” ZJetMax - Jet height [m] (used only for JET velocity profile, valid 70-490 m)
“default” 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^2/s^2] (or “default” or “none”)
“default” PC_UV - Hub mean u’v’ Reynolds stress [m^2/s^2] (or “default” or “none”)
“default” PC_VW - Hub mean v’w’ Reynolds stress [m^2/s^2] (or “default” or “none”)

--------Spatial Coherence Parameters----------------------------
“NONE” SCMod1 - u-component coherence model (“GENERAL”,“IEC”,“API”,“NONE”, or “default”)
“NONE” SCMod2 - v-component coherence model (“GENERAL”,“IEC”,“NONE”, or “default”)
“NONE” SCMod3 - w-component coherence model (“GENERAL”,“IEC”,“NONE”, or “default”)
“default” InCDec1 - u-component coherence parameters for general or IEC models [-, m^-1] (e.g. “10.0 0.3e-3” in quotes) (or “default”)
“default” InCDec2 - v-component coherence parameters for general or IEC models [-, m^-1] (e.g. “10.0 0.3e-3” in quotes) (or “default”)
“default” InCDec3 - w-component coherence parameters for general or IEC models [-, m^-1] (e.g. “10.0 0.3e-3” in quotes) (or “default”)
“default” CohExp - Coherence exponent for general model [-] (or “default”)

--------Coherent Turbulence Scaling Parameters-------------------
“M:\coh_events\eventdata” CTEventPath - Name of the path where event data files are located
“Random” CTEventFile - Type of event files (“LES”, “DNS”, or “RANDOM”)
true Randomize - Randomize the disturbance scale and locations? (true/false)
1 DistScl - Disturbance scale [-] (ratio of event dataset height to rotor disk). (Ignored when Randomize = true.)
0.5 CTLy - Fractional location of tower centerline from right [-] (looking downwind) to left side of the dataset. (Ignored when Randomize = true.)
0.5 CTLz - Fractional location of hub height from the bottom of the dataset. [-] (Ignored when Randomize = true.)
10 CTStartTime - Minimum start time for coherent structures in RootName.cts [seconds]

When I try to plot the average PSDs of the simulations, I end up with the following figure:

Based on the plots, I see that the values of the intensity differ by a factor of 2 between the TurbSim data and the analytical equation provided by TurbSim. For my case in the analytical equation, I have an L_K value of 8.10.760 = 340.2m, umeanhub = 14 m/s, and sigma_u = 2.254 m/s. I was wondering if there is something wrong in the process of trying to retrieve the PSD.

Michael Lingad

Dear @Michael.Lingad,

I’m not sure, but I expect that if you integrate the PSD across frequency, you’d get the standard deviation you expect. Which PSD is returning the correct standard deviation?

Best regards