The ventilative cooling potential of a perforated ceiling in combination with attic ventilation during the night in naturally ventilated residential buildings in tropical climate is investigated. 3D steady Reynolds-averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) simulations were carried out with the RNG k-ε turbulence model under non-isothermal conditions for two different single zone realistic building models, C1 (building without perforated ceiling and attic ventilation) and C2 (with perforated ceiling (40% porosity) and attic ventilation). The simulations were conducted for nighttime conditions in Indonesia (Makassar), as obtained from measured weather data, to represent real-life conditions as much as possible. The CFD simulations were performed for the wind direction perpendicular to the building facade with the window openings. The heat removal effectiveness (HRE) and air changes per hour (ACH) were assessed for both building configurations. The results show that building C2 facilitates a faster removal of heat from the occupied zone compared to building C1. This leads to a reduction of indoor air temperature that is lower by 0.8 °C for case C2 compared to case C1. Moreover, C2 displays higher values for both HRE (1.25 vs. 1.00) and ACH (34.1 h -1 vs. 27.9 h -1 ).
This paper briefly presents some of the headlines of an extensive comparison study of three different calculation models for wind-driven rain (WDR) on building facades. The three models are the semi-empirical model in the European Standard Draft for WDR assessment (ESD; [1]), the semi-empirical model by Straube and Burnett (SB; [2]) and the CFD model by Choi [3] extended by Blocken and Carmeliet [4]. These three models are applied to determine the WDR coefficient on the windward facade of a low-rise cubic building, a wide low-rise building, a wide high-rise building and a tower building, under steady-state conditions of wind and rain. In each case, the reference wind direction is perpendicular to the windward facade. CFD validation was performed earlier based on wind tunnel measurements and full-scale on-site WDR measurements. The CFD simulations of the WDR coefficient are considered as the reference case, and the performance of the two semi-empirical models is evaluated by comparison with these CFD results. The full study will be reported in the journal Wind and Structures [5,6].
In the present paper the cross-ventilation of an isolated building immersed in a neutral atmospheric boundary layer (ABL) with openings on the windward and leeward facades is investigated by means of numerical simulations at wind tunnel scale. Specifically, the large eddy simulation (LES) approach is employed, with a wall shear stress model at the bottom of the computational domain in order to take into account ground roughness. Three different inflow methods, i.e. a precursor method, the vortex method and the spectral synthesizer, are employed to generate the turbulent velocity profiles at the inlet of the computational domain. The numerical simulations are validated through wind tunnel test data available in literature and a statistical analysis is performed using common validation metrics. Results show that the choice of the inflow generator has a qualitative and quantitative influence on the predicted flow field and time-averaged concentration. Specifically, the precursor method and the vortex method provide similar results in terms of mean streamwise velocity, whereas the spectral synthesizer differs from the other two inflow generators in terms of predicted flow features (most notably a higher inclination of the ventilation jet). Slightly larger differences are observed for turbulence kinetic energy and time-averaged concentration, which are most accurately predicted by the precursor method. Nevertheless, despite the higher computational cost (+33%) of the precursor method, the performance difference with especially the vortex method is limited. In addition, both precursor method and vortex method outperform the spectral synthesizer for both turbulence kinetic energy and time-averaged concentration in most metrics. In conclusion, the vortex method can be considered the most cost-effective among the inflow generators employed for the case examined.
Large eddy simulation (LES) is widely used to investigate the aerodynamics and convective heat transfer (CHT) at the surfaces of sharp-edged bluff bodies for a wide range of Reynolds (Re) numbers. Due to the heavy computational costs associated with implicit filtering in LES at high Reynolds number flows (Re ≥ 105), wall-modeled (WM) rather than wall-resolved (WR) LES is often adopted. However, the performance of LES-WM for such applications has not yet been systematically investigated. Therefore, this study evaluates the performance of LES-WM and LES-WR for the flow and thermal field at the facades of a low-rise building immersed in an atmospheric boundary layer. Four grids are constructed for LES-WM, each employing different resolution at the building surfaces reaching maximum non-dimensional wall distance y+ = 43, 57, 70, and 95. In addition, the performance of two wall functions, namely the Werner and Wengle and the enhanced wall function is investigated. The results show that the use of LES-WM can result in significant deviations in the predicted near-facade flow pattern and the surface convective heat transfer coefficient (CHTC). Grid resolution significantly impacts the CHTC results and deviations go up to 88% (at the base of the windward facade). Considerable deviations among the employed wall functions are apparent only on the finest grid. In this case, the implementation of the enhanced wall function indicates better performance compared to the non-blended law of the wall (combined with the Werner and Wengle) for CHTC in the regions of the leeward facade where the flow remains attached to the wall. The deviation of the enhanced wall function for surface-averaged CHTC is found to be 10.8% against the wall-resolved LES results, while for the non-blended law of the wall 19.2%.
status: Published
Within a time span of only a few months, the SARS-CoV-2 virus has managed to spread across the world. This virus can spread by close contact, which includes large droplet spray and inhalation of microscopic droplets, and by indirect contact via contaminated objects. While in most countries, supermarkets have remained open, due to the COVID-19 pandemic, authorities have ordered many other shops, restaurants, bars, music theaters and indoor sports centers to be closed. As part of COVID-19 (semi)lock-down exit strategies, many government authorities are now (May-June 2020) allowing a gradual re-opening, where sometimes indoor sport centers are last in line to be permitted to re-open. This technical note discusses the challenges in safely re-opening these facilities and the measures already suggested by others to partly tackle these challenges. It also elaborates three potential additional measures and based on these additional measures, it suggests the concept of a certificate of equivalence that could allow indoor sports centers with such a certificate to re-open safely and more rapidly. It also attempts to stimulate increased preparedness of indoor sports centers that should allow them to remain open safely during potential next waves of SARS-CoV-2 as well as future pandemics. It is concluded that fighting situations such as the COVID-19 pandemic and limiting economic damage requires increased collaboration and research by virologists, epidemiologists, microbiologists, aerosol scientists, building physicists, building services engineers and sports scientists.
