Wind tunnel determination of the roughness length as a function of the fetch and the roughness density of three-dimensional roughness elements

Abstract

The roughness length (y0) has been evaluated from wind tunnel tests for various distributions of roughness elements at a number of stages in the growth of the associated boundary layer. Hence the variation of this parameter as a function of both fetch and roughness element density has been established and a semi-empirical expression for y0 derived. It can be deduced from the results that a distance of approximately 1000 roughness element heights is needed in order to achieve near-equilibrium boundary layer flow.