PURPOSE@ SCOPE AND APPLICABILITY OF THIS ITEM Turbulence data are required for engineering calculations of gust speeds (see ESDU 830456) and mean and fluctuating loading. In particular@ spectral densities are required as input data for methods used in assessing dynamic response. The definition of the properties described in this Item and other background information are given in Reference 3. The purpose of this Item@ which supersedes ESDU 74031@ is to provide the statistical properties of turbulence in the atmospheric boundary layer at a single point in space. The properties of turbulence at two points in space are dealt with in Reference 4. In this Item the properties considered are: (i) intensities and Reynolds stresses@ (ii) probability densities@ (iii) spectral densities and integral length scales of turbulence. The statistical properties presented are derived from world-wide measurements in the atmospheric boundary layer and@ within the uncertainties of the data@ can be taken to apply for neutral atmosphere* conditions which include strong winds (V10 gt; 10 m/s). The data are mainly based on measured values for homogeneous terrain (e.g. open country or forests) but some measurements are available for built-up areas and these indicate that@ within the scatter of the data@ the present model is applicable for heights greater than about 10 m above the general level of ground obstructions. When the upwind fetch of uniform terrain is less than about 30 km the effect of roughness changes should be considered (see Section 8). For very hilly or mountainous terrain the spectral data in Section 6 do not apply. In such cases secondary peaks in the normalised spectra (nSii/?? 2) may occur at low frequencies (see@ for example@ Derivation 27). Some additional data for complex terrain are provided in Derivation 44. The principal difference between the data presented in this Item and previous data (for example in ESDU 74031 which this Item supersedes) is that this Item recognises that the characteristic properties of turbulence (variances and length scales) are dependent on wind speed (except in a layer close to ground level). The reason for this is that the present data are based on similarity theory which shows that as the reference wind speed increases@ the boundary layer depth increases and the typical size and intensity of turbulence within the boundary layer are then scaled accordingly. Sections 3 to 7 present the data for uniform terrain (equilibrium boundary layer) conditions. Section 8 provides guidance on the effect of step changes in terrain roughness upwind of the site. Section 9 discusses the uncertainty of the data. The Appendices contain the equations from which the graphical data are obtained and gives the background to their derivation and to the methods given in the main part of the Item. The full methods on which this Data Item is based have been programmed into the software package@ ESDUpac A9232@ described in ESDU 92032. * See Items 820265 for a further explanation of this term and its applicability to the strong wind condition.
ESDU 85020 F-1993 history
1993ESDU 85020 F-1993 CHARACTERISTICS OF ATMOSPHERIC TURBULENCE NEAR THE GROUND. Part II: single point data for strong winds (neutral atmosphere)