Abstract
In this paper, the ventilation performances of (1) isothermal street canyons of different building-height-to-street-width (aspect) ratios (h/b) and (2) a ground-heated street canyon of h/b=1 at different Richardson numbers (Ri) are examined numerically by solving the Reynolds-averaged Navier-Stokes (RANS) equations with the use of the Renormalization Group (RNG) k-ɛ turbulence model. The mean (\( \overline {ACH} \)) and turbulent (ACH’) air exchange rates (ACH) are calculated by the eddy-viscosity model instead of the turbulence kinetic energy (TKE) used elsewhere. For the isothermal street canyons, the ACH’ is found to account for 90% of the total ACH for 0.5 ≤ h/b ≤ 2. Similar to the previous large-eddy simulation (LES) and k-ɛ turbulence model, the magnitudes and shapes of the roof-level profiles of mean and fluctuating vertical winds are close to each other for different h/b. This suggests that turbulent mixing is important for the ventilation of isothermal street canyons. For the ground-heated street canyon, both the mean wind and turbulence are strengthened as illustrated by the increasing \( \overline {ACH} \) and ACH’ with decreasing Ri. A secondary recirculation is developed at the ground-level windward corner that pushes the primary recirculation upward and enhances and ACH as well.
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