PURPOSE AND SCOPE OF THIS DATA ITEM

Values of the characteristic properties of atmospheric turbulence, such as intensity and integral length scales of turbulence, are required in the evaluation of the fluctuating loading induced in a structure by turbulence in the wind. Within the atmospheric boundary layer these properties are controlled by the nature of the underlying terrain and also by the strength of the wind. Items 84011 and 84030 provide tables of wind speed factors and turbulence intensity values for various terrains with or without ground roughness changes upwind of the site.

The purpose of this Item is to provide a complementary set of Tables giving the longitudinal integral length scales of the u-component of turbulence, x_Lu, (to which all other length scales can be related). The Index Tables in Section 4 indicate the range of terrain conditions for which data are presented and these include situations where roughness changes occur upwind of a site. The dependency of length scales on wind speed is important and so a simple correction factor is included for use with the tabulated data which are applicable for a reference wind speed,V_10r, of 20 m/s.

The equations for evaluating length scales of turbulence over terrain with roughness changes are detailed in ESDU 85020¹ (with Amendment E). The data in this Item have been generated using those equations.

The listing of a computer program to calculate local values of all integral length scales (and other wind speed and turbulence properties) is given in ESDU 01008³ for flat or hilly sites in terrain with multiple roughness changes. The relationships between length scales are given in Section 3.1.