Numerical studies on issues of Re-independence for indoor airflow and pollutant dispersion within an isolated building

This study conducted the numerical models validated by wind-tunnel experiments to investigate the issues of Re-independence of indoor airflow and pollutant dispersion within an isolated building. The window Reynolds number (Re(w)) was specified to characterize the indoor flow and dispersion. The indicators of RRC (ratio of relative change) or DR (K_DR) (difference ratio of dimensionless concentration) ≤ 5% were applied to quantitatively determine the critical Re(w) for indoor flow and turbulent diffusion. The results show that the critical Re (Re(crit)) value is position-dependent, and Re(crit) at the most unfavorable position should be suggested as the optimal value within the whole areas of interest. Thus Re(H,crit) = 27,000 is recommended for the outdoor flows; while Re(w,crit) = 15,000 is determined for the indoor flows due to the lower part below the window showing the most unfavorable. The suggested Re(w,crit) (=15,000) for indoor airflow and cross ventilation is independence of the window size. Moreover, taking K_DR ≤ 5% as the indicator, the suggested Re(w,crit) for ensuring indoor pollutant diffusion enter the Re-independence regime should also be 15,000, indicating that indoor passive diffusion is completely determined by the flow structures. The contours of dimensionless velocity (U/U(0)) and concentration (K) against the increasing Re(w) further confirmed this critical value. This study further reveals the Re-independence issues for indoor flow and dispersion to ensure the reliability of the data obtained by reduced-scale numerical or wind-tunnel models.