Flow and dispersion in coupled outdoor and indoor environments: Issue of Reynolds number independence. (March 2019)

• Record Type: Journal Article
• Authors: Dai, Yuwei; Mak, Cheuk Ming; Ai, Zhengtao
• Is Part Of: Building and environment. Volume 150(2019)
• Page Start: 119
• Page End: 134
• Publication Date: 2019-03
• Subjects: Reynolds number independence criteria -- Coupled outdoor and indoor environment -- Natural ventilation -- Pollutant dispersion -- CFD simulation; Buildings -- Environmental engineering -- Periodicals; Building -- Research -- Periodicals; Constructions -- Technique de l'environnement -- Périodiques; Electronic journals; 696
• DOI: 10.1016/j.buildenv.2019.01.008
• Languages: English
• ISSNs: 0360-1323

Abstract

Abstract: The Reynolds number ( R e ) independence criteria for flow and dispersion around purely outdoor environments has been examined in many previous studies, but little attention has been paid to the coupled outdoor and indoor environments. This study investigated the R e independence criteria of flow and dispersion in coupled outdoor and indoor environments using Computational Fluid Dynamics (CFD) with Large Eddy Simulation (LES) model. Two geometrical arrangements were considered, namely an isolated multi-story building, and an array of multi-story buildings. Four parameters including the non-dimensional air velocity, pollutant concentration, ventilation rate, and re-entry ratio were used to assess the R e independence criteria. The tracer gas decay method was used to predict the ventilation rate and to quantify the re-entry ratio for each room. Using the quantitative indicator, the deviation rate (DR), of the non-dimensional velocity below 5%, two sets of critical values were proposed: R e H based on the building height equal to 4.8 × 10 4 for the outdoor environment, and R e W based on the opening height equal to 1.4 × 10 4 for the indoor environment. The concentration field was more difficult to meet the R e -independent requirement. Using the DR of the non-dimensional concentration below 5%, the critical values were R e H = 7.9 × 10 4 and R e W = 3.0 × 10 4 . If the DR was enlarged to 10%, the R e H and R e W criteria for the concentration field were the same as the velocity fields. For the non-dimensional ventilation rate and re-entry ratio, the critical value for the R e independence was R e W = 1.4 × 10 4 for both the isolated buildings and the building arrays. Highlights: Two sets of criteria for achieving R e -independence proposed for coupled environments. R e -independent issue investigated for both an isolated building and building arrays. Four parameters — air velocity, pollutant concentration, ventilation rate and re-entry ratio —assessed. Tracer gas decay method used to calculate ventilation rate and re-entry ratio. R e –independence achieved for dimensionless ventilation rate and re-entry ratio.