Abstract:

ESDU 86035 provides complementary data on integral length scales to those in ESDU 85020 and 86010, which are principally concerned with terrain uniform for at least 50 km (31 miles) upwind of the site. In practice there are often terrain roughness changes near the site which have an important effect on the length scales. For example, the change from open country to a site 1 km into a built-up area will reduce length scales by about 30 per cent below 30 m (100 ft) and by about 50 per cent at greater heights. A method of taking account of such roughness changes is described in ESDU 85020 but is not convenient for hand calculation. ESDU 86035 gives tables of values of the longitudinal length scale for the longitudinal (along-wind) turbulence velocity component (from which the other eight length scales are readily obtained) for combinations of terrain changes of most interest and for a range of wind speeds. The data relate to uniform terrain and to terrain with one or two roughness changes.