Numerical studies on Re-independence and influence region definition for flow and dispersion within street-indoor scale model

Abstract

To reduce modeling errors and save computing resources, the reduced-scale numerical models may sometimes be used. This study conducted the numerical models validated by wind-tunnel tests to investigate Re-independence issue and influence region definition for flow and dispersion within the target street-indoor scales. The window Re (Rew) was specified to characterize the indoor flow and dispersion, and the indicator of DR was applied to quantitatively determine Rew,crit. The ventilation modes (cross ventilation, CV or single-sided ventilation, SSV) and the surrounding building effect on Re-independence of indoor flow and dispersion were examined. Then ACH (air exchange rate) varying with the increasing layer number (n) of surrounding buildings was applied to derive the required size of influence region. Results show that it needs different Rew,crit to ensure the indoor flow structures at different positions to enter the Re-independence regimes, that is, the Rew,crit is a position-dependence quantity. Taking difference ratio (DR) ≤ 5% as the threshold, Rew,crit (=15,000) at the most unfavorable position should be selected as the optimal value to ensure Re-independence of indoor flow and dispersion, and the suggested Rew,crit is independent of ventilation modes and surrounding buildings. The ACH distributions show the required size of influence region to ensure the flow structures within the target street-indoor scales remain unchanged is n = 5. The contours of normalized velocity and pollutant concentration further confirm this required layer number. This study can provide significant guidelines for accurately modeling the flow and dispersion within the coupled indoor-outdoor scales by reduced-scale numerical model.