Pedestrian-level wind conditions around buildings:review of wind-tunnel and CFD techniques and their accuracy for wind comfort assessment

Information on pedestrian-level wind (PLW) speed for wind comfort assessment can be obtained by wind-tunnel measurements or Computational Fluid Dynamics (CFD) simulations. Wind-tunnel measurements for PLW are routinely performed with low-cost techniques such as hot-wire or hot-film anemometers, Irwin probes or sand erosion, while Laser-Doppler Anemometry (LDA) and Particle-Image Velocimetry (PIV) are less often used because they are more expensive. CFD simulations are routinely performed by the relatively low-cost steady Reynolds-Averaged Navier-Stokes (RANS) approach. Large-Eddy Simulation (LES) is less often used because of its larger complexity and cost. This paper reviews wind-tunnel and CFD techniques to determine PLW speeds expressed generally in terms of amplification factors defined as the ratio of local mean wind speed to mean wind speed at the same position without buildings present. Some comparative studies systematically indicate that the low-cost wind-tunnel techniques and steady RANS simulations can provide accurate results (+/-10%) at high amplification factors (> 1) while their accuracy can deteriorate at lower amplification factors (< 1). This does not necessarily compromise the accuracy of PLW comfort assessment, because the higher amplification factors provide the largest contribution to the discomfort exceedance probability in the comfort criterion. Although LDA, PIV and LES are inherently more accurate techniques, this paper supports the continued use of faster and more inexpensive techniques for PLW studies. Extrapolating a previous saying, we argue that pedestrian-level wind comfort is one of the few topics in wind engineering where nature is kind to us concerning turbulent flows