A common practice, adopted by several building energy simulation (BES) tools, is the use of surface averaged wind pressure coefficients (Cp) instead of local Cp values with high resolution in space. The aim of this paper is to assess the uncertainty related to the use of surface averaged data, for the case of a cubic building with two openings. The focus is on wind-driven ventilation and infiltration, while buoyancy is not taken into account. The study is performed using published empirical data on pressure coefficients obtained from wind tunnel tests. The method developed to calculate the uncertainty is based on comparison of: the flow rate calculated using the averaged values (φAV), and the one calculated using local values (φLOC). The study considers a large number of combinations for the opening positions in the facade. For each pair of openings (i), the values of φLOC_i and φAV_i are calculated. Based on the ratio between φLOC_i and φAV_i the relative error (ri) is calculated. The relative error is presented statistically, providing probability density graphs and upper and lower bounds for the confidence interval (CI) of 95%. For this CI, the conclusion is that 0.24 φAV < φLOC < 4.87 φAV.
This chapter focuses on modelling aspects of some important moisture phenomena in whole building simulations. The term ‘whole building’ refers to the outside environment of buildings (microclimate), the building envelope and the indoor environment of buildings. In particular, this chapter treats computational modelling of moisture buffering in rooms, computational modelling of wind-driven rain and computational modelling of convective heat and moisture transfer at exterior building surfaces. The chapter is primarily oriented to the deterioration of building materials due to high variations of relative humidity or wind-driven rain. However, the methodology and computational models can be extended to analyse the effect of moisture on other issues like energy consumption in buildings, hygrothermal comfort, indoor air quality and the reduction of active cooling in urban heat islands by means of evaporative cooling.
Abstract Aerodynamic drag is the main resistive force in cycling at high speeds and on flat terrain, so reducing it is critical to improving cyclist performance. Aerodynamic comparisons have been made in the past between different types of wheels, and disk wheels were often the best performers. However, to the best of our knowledge, there are no studies in the available literature on how modifications to the disk wheel geometry can improve its performance. Therefore, this paper studies and compares the aerodynamics of disk wheels with flat side disks and with curved side disks (lenticular). Moreover, semilenticular front wheels with an asymmetrical shape are introduced. All but one of the simulated (semi-)lenticular wheels perform better than the flat disk wheels at all yaw angles, e.g., the maximum CD reduction was 5.5%, 10.9%, and 87.5% at 0 deg, 4 deg, and 8 deg yaw angle, respectively. Semilenticular wheels provide a lower CD at medium and large yaw angles compared to corresponding symmetric lenticular wheels. Moreover, the large influence of the ratio of tire width to wheel width on the aerodynamic drag of cycling wheels is confirmed. These results will help riders in their wheel choice and will help manufacturers to design future disk wheels.
Wind flow in urban areas is strongly affected by the urban geometry. In the last decades most of the geometries used to reproduce urban areas, both in wind-tunnel (WT) tests and Computational Fluid Dynamics (CFD) simulations, were simplified compared to reality in order to limit experimental effort and computational costs. However, it is unclear to which extent these geometrical simplifications can affect the reliability of the numerical and experimental results. The goal of this paper is to quantify the deviations caused by geometrical simplifications. The case under study is the district of Livorno city (Italy), called "Quartiere La Venezia". The 3D steady Reynolds-averaged Navier-Stokes (RANS) simulations are solved, first for a single block of the district, then for the whole district. The CFD simulations are validated with WT tests at scale 1:300. Comparisons are made of mean wind velocity profiles between WT tests and CFD simulations, and the agreement is quantified using four validation metrics (FB, NMSE, R and FAC1.3). The results show that the most detailed geometry provides improved performance, especially for wind direction α = 240° (22% difference in terms of FAC1.3).
Information on wind conditions in harbors and wind loads on ships is important for safe maneuvering and mooring of ships. The wind conditions in harbors are very complex and characterized by a multitude of internal atmospheric boundary layers due to the large variations in terrain roughness. This paper presents the development of data to support a software application for assessment of wind conditions in the Port of Rotterdam. An extensive measurement campaign using ultrasonic anemometers was performed in the harbor during a period of 6 months. These measurements were compared with the numerical simulations with Computational Fluid Dynamics (CFD) on a high-resolution grid. This comparison showed a good agreement for such a complex heterogeneous terrain. 89% of the simulated amplification factors (?=Ump/Ump1) were within the range of the mean measured amplification factors ± two times the standard deviation. These data will be used in the near future to support a software application for the harbor authorities and tugboat pilots to allow improved safety, maneuverability and mooring of container ships.
Wind comfort around a high-rise building in a complex urban environment is studied by combining Computational Fluid Dynamics (CFD) with the Dutch wind nuisance standard NEN 8100. The CFD simulations are performed with the 3D steady Reynolds-averaged Navier-Stokes (RANS) equations and the realizable k-ε model. Simulations are conducted according to best practice guidelines in CFD and are compared with on-site measurements at three street positions. The study shows that the highrise building is the main cause of the wind nuisance at its base, as it catches the oncoming wind and deviates it to pedestrian level. Therefore, as a remedial measure, different sizes of canopies attached to the tower on both the south-southwest and the east-southeast side are studied.
This paper briefly discusses the need of high-resolution whole-building numerical modelling in the context of climate change. High-resolution whole-building numerical modelling can be used for detailed analysis of the potential consequences of climate change on buildings and to evaluate remedial measures. This discussion is certainly not intended to be complete. Rather it is intended to provide some views on climate change and built environment from a computational building physics perspective. After this brief discussion, a case study of application and validation of a high-resolution sub-model is presented, in which Computational Fluid Dynamics (CFD) is used to calculate wind-driven rain (WDR) deposition on a monumental tower building in the Netherlands.
Knowledge of the pressure distributions on building surfaces is essential for a complete understanding of infiltration, wind-induced ventilation and wind loads. Earlier studies have shown the influence of different facade appurtenances like balconies on the wind-induced pressure on building facades. However, a detailed investigation of the impact of facade appurtenances on the pressure distribution on building facade has not yet been performed. This is especially the case for high-rise buildings. This paper, therefore, presents a detailed study on mean wind pressure distributions on the windward facade of a high-rise building with and without facade appurtenances at wind direction of 0°. The realizable k-ɛ turbulence model in 3D steady Reynolds-Averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) is used for predicting. The evaluation is based on validation with wind-tunnel measurements. The results show that the presence of balconies can significantly influence the Cp distributions on the windward facade. This influence greatly depends on the size and geometry of balconies.
