ESDU 86035:2011

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.