TurbSim User's Guide: Version 1.06.00 - NREL

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Cohi,j( f )iiSij( f )( ) ( )= , (49)S f S fwhere f is the frequency, S ii is the power spectral density as defined in the Spectral Modelssection, and S ij is the cross-spectral density. This coherence adds correlation between the samewind components at two spatially separated points (e.g., u i -u j correlation, not u-v correlation).The coherence functions that are implemented in TurbSim are described below.Coherence for IEC Spectral ModelsThe coherence function for the u-component of the IEC spectral models is defined as⎛2⎜ ⎛ fr⎞⎛Cohi, jexp a0.12 r ⎞= ⎜− +⎜u⎟ ⎜ L ⎟c⎜ ⎝⎝ ⎠hub ⎠⎝jj2⎞⎟⎟, (50)⎟⎠where f is the frequency, r is the distance between points i and j on the grid, a is the coherencedecrement, u is the mean hub-height wind speed, and Lhubc is a coherence scale parameter. ForIEC 61400-1 2 nd ed. [23], the parameters a and L c area = 8.8Lc( HubHt)= 2.45min 30m, ,(51)where the function min ( ) is the minimum of 30 meters and HubHt. For IEC 61400-1 3 rd ed.[20], the parameters area = 12Lc( HubHt)= 5.67 min 60m, .(52)The IEC 61400-1 standard does not specify coherence for the v or w wind-speed components. InTurbSim, the coherence for the v and w components of the IEC spectral models is implementedusing the identityCohi,j⎧1= ⎨⎩0i =i ≠j. (53)jCoherence for Non-IEC Spectral ModelsThe coherence function for all three of the wind components, K = u, v, w, for the non-IECspectral models is defined as⎛Cohi, j= exp⎜− aKK+ bKrm⎜⎝ um⎠⎝2CohExpr⎛ fr⎞( z ) ⎜⎟( )2⎞⎟, (54)⎟⎠40
where r is the distance between points i and j, z m is the mean height of the two points, and u m isthe mean of the wind speeds of the two points (over the entire simulation). The variables a and bare the input coherence decrement and offset parameter, respectively, which are defined by thevalues of the IncDec1, IncDec2, and IncDec3 input parameters (for each of the components).Their default values are discussed in the Input File section of this document and are plotted inFigure 13 through Figure 15.This coherence model is based on the form suggested by Thresher et al. [34] and implemented inrthe IEC coherence model. The ( )mCohExpz term has been added to allow users to implementSolari’s coherence definition [35]. Note that if b = 0 and CohExp = 0, this equation also becomesthe Davenport coherence model [36].Wind (Velocity) ProfilesTurbSim offers users a choice of mean wind (velocity) profiles. The velocity profiles determinethe mean u-component velocity at each height for the length of the simulation. By definition, themean v- and w-component velocities are zero. Wind-direction profiles determine the meanhorizontal wind direction at each height. A wind-direction profile is calculated with the low-leveljet wind-speed profile, but direction profiles are not calculated with the other velocity profiles.When computing the mean velocity profile, TurbSim uses the inputs URef and RefHt as thereference point to calculate the mean velocity at HubHt, u . The velocities at other heights thenhubare calculated using u and HubHt as the reference point. Figure 23 shows an example of fourhubdifferent types of mean velocity profiles that were generated using default boundary conditionsand RICH_NO = 0.05 with the GP_LLJ model. For each of the velocity profiles plotted in thefigure, URef = 12 m/s and RefHt = HubHt = 90 m.Power-Law Wind ProfileThe power-law mean velocity profile uses the PLExp input parameter to calculate the averagewind speed at height z using the equation⎛ z ⎞= ⎜z ⎟⎝ ref ⎠( ) u( zref)u zPLExp, (55)where u( z ) is the mean wind speed at z and z ref is a reference height above ground where themean wind speed u( zref ) is known.Logarithmic Wind ProfileThe diabatic (logarithmic) wind profile calculates the average wind speed at height z using theequation( ) = u( zref)u zlnlnz( Z0 )z( )refZ0−ψm, (56)−ψm41
Page 4 and 5: AcknowledgementsTurbSim was written
Page 6 and 7: Table of ContentsAcknowledgements .
Page 8 and 9: List of FiguresFigure 1. TurbSim si
Page 10 and 11: Figure G-6. Unstable velocity spect
Page 12 and 13: Buhl added the ability to generate
Page 14 and 15: “CertTest.bat” and set the envi
Page 16 and 17: TurbSim assumes that parameters are
Page 18 and 19: parameter RICH_NO) is greater than
Page 20 and 21: UsableTime: Usable Time Series Leng
Page 22 and 23: however, because AeroDyn—in its i
Page 24 and 25: Figure 8. Coherent turbulent kineti
Page 26 and 27: Figure 9. Default jet wind speed fo
Page 28 and 29: ⎛1000⎞θ = T ⎜ ⎟⎝ p ⎠0.
Page 30 and 31: The three α variables are coeffici
Page 32 and 33: IncDec2: Spatial Coherence for the
Page 34 and 35: Table 8. Valid CTEventFile EntriesI
Page 36 and 37: files a “.bin” extension. At ea
Page 38 and 39: generated for the FF Bladed-style
Page 40 and 41: Spectral ModelsTurbSim uses a modif
Page 42 and 43: K( )S f = UStar2s1, K⎛ z ⎞⎛φ
Page 44 and 45: NWTCUP: The NREL National Wind Tech
Page 46 and 47: Figure 20. GPLLJ-model stable/neutr
Page 48 and 49: (NumPeaks K = 2, K = u, v, w) and e
Page 52 and 53: where u( z ) is the mean wind speed
Page 54 and 55: atmosphere. To obtain more events w
Page 56 and 57: See Appendix H in this document for
Page 58 and 59: • The statistics calculated in th
Page 60 and 61: References[1] Laino, D. J.; Hansen,
Page 62 and 63: [28] Olesen, H.R.; Larsen, S.E.; H
Page 64 and 65: Appendix B: TurbSim Quick-Start Gui
Page 66 and 67: Appendix C: Flow ChartsTurbSim Inpu
Page 68 and 69: TurbSim InputFileTurbine/Model Spec
Page 70 and 71: TurbSim InputFileMeteorologicalBoun
Page 72 and 73: TurbSim Input FileDefault Input Val
Page 74 and 75: Appendix D: Full-Field TurbSim Bina
Page 76 and 77: Appendix E: Full-Field Bladed-Style
Page 78 and 79: Appendix F: Tower Data Binary File
Page 80 and 81: Appendix G: Velocity Spectra Compar
Page 82 and 83: Default UStar (m/s)SMOOTH 0.644NWTC
Page 84 and 85: Default UStar (m/s)SMOOTH 0.656NWTC
Page 86 and 87: Appendix H: Sample AeroDyn Coherent

TurbSim User's Guide: Version 1.06.00 - NREL

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