CFD investigation on the effects of wind and thermal wall-flow on pollutant transmission in a high-rise building

Abstract

The solar radiation can heat the building outer surface, and then cause the upward natural convection flows adjacent to the wall. This phenomenon is especially obvious on a windless sunny day. The near wall thermal plume can drive gaseous pollutants released from lower floors to upper floors. Combined with the effect of ambient approaching wind, the transmission routes will be very complicated. The paper aims to investigate the airflow patterns and pollutant transmission within a building under the effects of wind and thermal forces. A hypothetical twenty-storey slab-shape high-rise building in Shanghai with single-sided natural ventilation is set as the research object in the present study. The intensity of solar radiation on a typical day during transition season is theoretically analysed. The temperature difference between the heated building envelope and the ambient air is calculated by a simplified heat balance model. Finally, the tracer gas method is employed in the numerical simulation to analyse the influence of the wind and wall thermal plume flow on the inter-flat pollutant transmission characteristics. The results show that, the temperature difference between sunward and shady side wall is about 10 K at noon on the designate day. When the source is set as a point with steady intensity and the buoyancy is stronger than or approximately equivalent to the wind, the reentry ratio of the flat immediately above the source can be around 25%.

Investigation of interunit dispersion in 2D street canyons: A scaled outdoor experiment

“…The symbol (○) indicates the mean value of each data group, and the symbol ( � ) at the top and bottom of the whiskers indicates the maximum and minimum values. ACH * is the dimensionless ventilation rate calculated by ACH * ¼ ACH U ⋅ V AW [27], where U represents the average background wind velocity, V represents the volume of each room, A W represents the window area. Noted that, the estimated ACH * of three tests during phase II (BL2, BL3 and BL4) has been adjusted to subtract the ventilation rate caused by the buoyancy effect (ACH B ) summarized in Table 4.…”

“…CFD simulations were also commonly used to investigate the interunit transmission. A series of numerical studies were conducted to further understand the influential factors of interunit dispersion, including the effects of buoyancy-dominated forces [15,[20][21][22], balconies [10,23,24], surrounding interfering buildings [25,26], and heated walls [27]. Different turbulence models were considered in the airflow and dispersion simulations, including a mean process with an advanced Reynolds-Averaged Navier-Stokes (RANS) model [10,23,25,26] and transient process with an Large-Eddy Simulation (LES) model [24,28].…”

Numerical investigation of gaseous pollutant cross-transmission for single-sided natural ventilation driven by buoyancy and wind

“…The impacts of time-dependent dynamics caused by the fluctuating ambient wind on heat and mass transfer were not considered. In addition, it has been reported by Mu et al [23] that the ACH calculations were slightly higher than the tracer gas decay method, while the results approximated those predicted by empirical models [23]. Nevertheless, the calculation of ACH based on the steady flow field from the RANS-based model was still widely used, in view of the desirable computing efficiency and detailed information that can be provided [18,23,52].…”

“…Compared with large eddy simulation and detached eddy simulation models, the RANS-based modeling approach significantly reduces the required computational power and resources [34,37]. Several studies have successfully employed RANS models to predict indoor and outdoor airflows in windward and leeward conditions [23,39]. The baseline k-ω turbulence model, which is a two-equation eddy-viscosity model, was also found to yield satisfactory accuracy and stability when modeling an indoor airflow [40].…”

“…The results indicated that low-speed winds induced pollutants to enter upper floors, whereas high-speed winds formed an air curtain near the building facade and restricted pollutant transmission between floors. Furthermore, Mu et al [23] used CFD to simulate the effects of solar radiation on the facade of a high-rise building and determined the impact of the facade's direction (sun-side or shade-side) on the re-entry of pollutants into the upper floors.…”