Investigation of Re -independence of turbulent flow and pollutant dispersion in urban street canyon using numerical wind tunnel (NWT) models

Abstract

Abstract This paper numerically and experimentally studied the Reynolds number independence (Re-independence) of turbulent flow and pollutant dispersion in urban areas. The concept of numerical wind tunnel (NWT) is proposed and validated by prototype wind-tunnel experimental measurements. A new physical quantity: the ratio of relative change, RRC, is proposed to investigate the Re-independence quantitatively. For the given street canyon, numerically predicted variations of RRC vs. building Reynolds number (ReH) from three k–ɛ turbulence models agree well with each other, and the variation trend shows that there exist two flow regimes in the range of ReH studied: flow in low ReH region is strongly affected by ReH, while that in higher ReH region is weakly affected by ReH, giving a strong support to the concept of Re-independence of turbulent flow. A criterion of RRC less than 5% is suggested to determine the value of the critical Reynolds number. For the street canyon studied, such determined critical building Reynolds number (ReH,crit) is 3.3 × 104. Examinations of dimensionless velocity contours, local velocity vectors, and concentration contours demonstrate the feasibility of the suggested critical Reynolds number.