Point-to-Point Scalar Transfer Efficiencies within a Cross-Ventilated Room Model Sheltered by Urban-Like Block Arrays

Using pressure difference, natural and cross-ventilation can deliver clean outdoor air into an indoor space. Many productive studies have been reported to evaluate the natural and cross-ventilation process, using experimental methods such as wind tunnel experiments, field measurements, and computational fluid dynamics (CFD) methods using RANS and LES. However, most of them have provided predictions of the ventilation rate and flow field as their primary agenda, with little discussion of how well this system contributes to indoor contamination control. Here, isothermal CFD simulations were performed for airflow and scalar concentration fields for cross-ventilation conditions sheltered by buildings. Heterogeneous ventilation efficiencies determined by scalar concentration distributions in the cross-ventilation room model were quantitatively analyzed using three indices: scale for ventilation efficiencies of 6, transfer probability (TP), and travel time (TT). The simultaneous analysis of TP and TT allowed a quantitative discussion of the scalar transfer mechanism from a local point to another in indoor space. On the other hand, although both SVE6 and TT are indices for residual lifetime from a point to the exhaust outlet, a certain difference in the residual lifetime was confirmed due to differences in the analysis process.