Modeling the neutrally stable atmospheric boundary layer for laboratory scale studies of the built environment

The properties of the atmospheric boundary layer (ABL) influence a range of physical phenomena in urban areas such as wind loading on buildings, wind-driven ventilation flows, pollution dispersion, and the lift off and transport of loose debris. In order to accurately model the ABL velocity profile at laboratory scale, it is important to establish the shear velocity u∗, surface roughness z0, and zero plane displacement d in either a wind tunnel or water flume. Current techniques for establishing these parameters are based on either an analysis of the boundary layer surface geometry or iterative curve fitting techniques that use mean velocity and/or turbulent kinetic energy profiles, occasionally combined with empirical correlations for z0. A new curve fitting method for calculating these logarithmic velocity profile parameters is presented. This new method calculates u∗, z0, and d directly from time-averaged velocity profile data in just two steps without any iteration. A comparison is presented between the results of the new method and other available methods applied to a range of velocity profile measurements in air and water. The comparison shows that, although the new method requires less data and fewer steps, it calculates u∗ and z0 with greater accuracy than existing techniques, and d with equivalent accuracy to existing techniques.

► New method for estimating surface roughness in lab boundary layer flows.
► New curve fitting technique is simple and non-iterative.
► Method is compared to a range of complex geometric and curve fitting techniques.