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/U₀) 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.