Influence of Atmospheric Boundary Layer Depth on the Ventilation Performance over Idealized Urban Surfaces

The aerodynamic resistance and the ventilation performance are measured by friction factor f and air exchange rate ACH, respectively. Preliminary results show that the friction factor decreases with increasing UBL depth, that in turn affects the ACH subsequently. In particular, the turbulent component of ACH (ACH”) is linearly proportional to the square root of friction factor. This finding is in line with our previous studies in which a monotonic behaviour between ACH” and (square root of) friction factor is exhibited regardless the geometry of building elements. In view of the consistent results obtained, it is hypothesised that the aerodynamic resistance (measured by friction factor) could be used as a single parameter of urban area ventilation performance. Additional CFD tests are undertaken based on a broad range of aspect ratio and UBL depth.