Abstract:

ESDU 91043 presents methods for estimating speed-up factors for mean wind speeds over hills, embankments, escarpments and valleys. The methods treat all regions of a hill, including shelter regions near the foot and account for the local profile. Three-dimensional effects and wind inclination to the ridge line can be taken into account. Interference effects from other nearby topography can be assessed, and guidance is provided for the effects of flow separation on steep topography. Two methods are given: a simple graphical approach that is accurate for simple embankments but is less accurate for rounded hills because it only accounts for the overall shape, and a more precise method that accounts for the detailed shape of the hill. Irregularly-shaped hills with bulges and depressions, and multiple hills, are treated by the method of superposition, that is, each irregularity is treated as a separate isolated hill or valley and the contribution to speed-up added to the other contributions for an overall solution. The methods were derived from data obtained using solutions of the Navier-Stokes equations, calibrated against both full-scale and wind-tunnel measurements.