Abstract:

The purpose of ESDU 01008 is to provide detailed information on the use of, and background to, the Excel Visual Basic module E0108. This module, which runs in Excel 97 or later, can be used to estimate the variation of wind speed and turbulence properties with height in the atmospheric boundary layer. The module brings together the relevant methods for estimating the effects of terrain roughness changes, gust averaging time and topography (hills, valleys, etc.) described in other ESDU Data Items. The spreadsheet presentation facilitates repeat runs with changes to the input. The facility is also available to reduce or correct measured wind properties (such as those from a local met. station) to values corresponding to standard conditions such as flat, uniform open country terrain, or to obtain corresponding values for some other terrain.

The program will calculate wind properties as a function of height over the site including hourly-mean wind speed and maximum gust speed, together with properties of the longitudinal (u) and lateral (v and w) components of turbulence (intensities, integral length scales and spectral densities). The program takes into account the following local conditions.

Ground roughness at the site and variations in ground roughness upwind of the site including lateral variations in a terrain patch and the variation of sea-surface roughness with wind speed.

Topographic effects on wind speed due to the location of the site in a hilly region, including ridges, embankments, escarpments or cliffs, or in a valley; topographic effects on turbulence properties for flow over hills with no flow separation.

A major feature of the program is its ability to deal with sites in complex terrain where the site is located within a range of hills. The general effect of topography is based on the two-dimensional computational method of Deaves but extended to include three-dimensional effects. The program incorporates a means of dealing with steep topography where flow separations occur and also a simplified model for estimating the distortion of spectra and turbulence variances over a hill.