Shelter behind two-dimensional solid and porous fences

Abstract

Using a pulsed-wire anemometer, extensive measurements have been made in the wakes of two-dimensional solid and porous fences immersed in the constant-stress region of a simulated rural atmospheric boundary-layer. The porosity (ratio of open to total area) of the perforated fences ranged from 0.0 to 0.5 and each porosity was modelled using three forms of openings, i.e. vertical slats, horizontal slats and circular holes. Comparative measurements made using the more conventional hot-wire anemometer are given. The results show the superiority of the pulsed-wire anemometer in correctly measuring the highly turbulent and sometimes recirculating wake flows. This indicates that previously reported experiments may be in considerable error. Results from the present experiment are given in the form of dimensionless mean and turbulence velocity profiles. In addition, contour plots of shelter parameters behind the fences are given for comfort and shelter analyses. Downstream of the re-attachment region, velocity deficits and excess shear and normal stress perturbations (quantities useful in shelter analyses) are plotted in a self-preserving form and simple equations that fit the experimental points are given. Power spectra measured in the presence of the solid fence are given and the structure of the turbulent wake deduced from these is discussed.