Consistency of mean wind speed in pedestrian wind environment analyses: Mathematical consideration and a case study using large-eddy simulation

When analyzing pedestrian wind environments, the evaluated mean wind speed sometimes varies in its definition depending on the method used, such as in wind tunnel experiments (WTEs) and in computational fluid dynamics (CFD) simulations. First, this study defined three types of mean wind speed (mean-vector speed, mean speed, and effective speed) and investigated their interrelations mathematically. Second, discrepancies between the three mean wind speeds were predicted quantitatively by conducting a large-eddy simulation of flow around a single building model in an urban boundary layer. Near the ground surface, the differences between the mean wind speeds became larger in the recirculation flow near the building's windward corners and in its wake. However, in the region where the maximum wind speeds occurred, all the mean wind speeds were similar. Finally, we presented a method to estimate mean speed, which is commonly evaluated in WTEs, using information that can be obtained from CFD using turbulence models based on Reynolds-averaged Navier-Stokes equations. By modeling the probability distribution of the instantaneous velocity in a multivariate Gaussian distribution, we demonstrated its ability to estimate mean speed with high accuracy.