Buildings are always found to be in the vicinity of other buildings, especially in urban areas. This causes effluents released from stacks located on one of the buildings to re-enter the same or an ...adjacent building, generating potential health problems to the occupants of the building. Earlier, Computational Fluid Dynamics (CFD) has been used in simulating pollutant transport for isolated buildings, with only few studies examining the effects of adjacent buildings. In this paper three cases that include an isolated low-rise building (source), a taller building placed upwind of the source and a case with taller buildings placed upwind and downwind of the source were considered. CFD simulations using the Realizable
k–
ε model for different turbulent Schmidt numbers (
Sc
t
) and wind tunnel experiments were performed for these cases.
ASHRAE, 2007 was also used to assess plume dispersion for the isolated building. It was found that a strong dependence of
Sc
t
on CFD simulations of pollutant transport exists for the isolated building configuration. However, variations of
Sc
t
have less impact on assessing pollutant dispersion in the presence of adjacent buildings. The
ASHRAE, 2007 model predicted very low dilutions for the isolated building, making it necessary to re-visit its formulations.
This article provides an overview of the application of computational fluid dynamics (CFD) in building performance simulation for the outdoor environment, focused on four topics: (1) pedestrian wind ...environment around buildings, (2) wind-driven rain on building facades, (3) convective heat transfer coefficients at exterior building surfaces and (4) air pollutant dispersion around buildings. For each topic, its background, the need for CFD, an overview of some past CFD studies, a discussion about accuracy and some perspectives for practical application are provided. This article indicates that for all four topics, CFD offers considerable advantages compared with wind tunnel modelling or (semi-)empirical formulae because it can provide detailed whole-flow field data under fully controlled conditions and without similarity constraints. The main limitations are the deficiencies of steady Reynolds-averaged Navier-Stokes modelling, the increased complexity and computational expense of large eddy simulation and the requirement of systematic and time-consuming CFD solution verification and validation studies.
This paper investigates the downwash effect of a rooftop structure (RTS) representing a typical RTS on plume dispersion. The effect of wind direction, exhaust speed, stack location, stack height, and ...RTS crosswind width on the severity of the downwash effect on the plume is assessed. Wind tunnel experiments were conducted to obtain plume centerline concentrations on the roof of typical low-rise and high-rise buildings. Measurements were obtained downwind of an RTS with height
h = 4 m, along-wind length
l = 8 m for 3 crosswind widths
w = 10 m, 20 m and 30 m. Flow visualization was also conducted to obtain a qualitative assessment of the flow downwind of the RTS. The downwash produced by the RTS caused a significant increase in roof level concentration depending on building height, stack location, stack height, exhaust speed, wind direction and RTS crosswind width. An attempt is made to provide design guidance for determining stack height required to avoid the downwash effect for an exhaust placed downwind of the RTS.
► Downwash due to a rooftop structure (RTS) on plume increased re-entrainment. ► Downwash effect depends on stack, RTS and building characteristics. ► Downwash effect decreases with increase in stack height and exhaust speed. ► Downwash leads to enhanced dilution and plume bending. ► Downwash effect of RTS is negligible for tall buildings.
Outdoor air pollution is a major current environmental problem. The precise prediction of pollutant concentration distributions in the built environment is necessary for building design and urban ...environmental assessment. Near-field pollutant dispersion, involving the interaction of a plume and the flow field perturbed by building obstacles, is an element of outdoor air pollution that is particularly complex to predict. Modeling methodologies have been discussed in a wide range of research fields for many years. The modeling approaches are categorized into field measurements, laboratory (wind and water tunnel) experiments, (semi-) empirical models, and computational fluid dynamics (CFD) models. Each of these approaches has advantages and disadvantages. It is therefore important to use due consideration for the underlying theory and limitations when applying these modeling approaches. This paper considers some of the most common questions confronting researchers and practitioners in the modeling of near-field pollutant dispersion in the built environment.
•Common questions in the modeling of pollutant dispersion around buildings are considered.•Near-field pollutant dispersion involves the interaction of plumes and wind flows.•Modeling approaches include field and laboratory experiments, empirical and CFD models.•It is important to consider the underlying theory and limitations prior to modeling.
This study performs computational fluid dynamics simulations for flow and dispersion fields around an isolated cubic building model with tracer gases being exhausted from an exit behind the building. ...The tracer gases have three different buoyancies according to the difference in density with ambient air and, therefore, behave as neutral, light, and heavy gases. The performance of steady Reynolds-averaged Navier–Stokes (RANS) simulations with the Boussinesq approximation is examined herein by comparing the simulation results with the experimental results for different plume buoyancies. The steady RANS computations can generally reproduce the impact of plume buoyancy on the mean concentration in the experimental results even if the model performance for heavy gases is better than that for light gases and worse than that for neutral gases. This tendency is closely related to the prediction accuracy of the mean velocity and turbulent kinetic energy behind the building, which is restricted by the steady RANS simulations. The study also confirmed that the buoyancy modeling in the ε equation shows a negligible influence on the results.
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•Steady RANS simulations for dispersion with plume buoyancies were performed.•The model performance was examined by comparing the results with experimental results.•CFD generally reproduced the impact of plume buoyancies on the mean concentration.•The model performance was affected by the prediction accuracy of the flow field.
Prediction accuracy of flow and dispersion around a cubic building with a flush vent located on its roof was examined using various
k–
ɛ models, and numerical results were compared with wind-tunnel ...data. Four types of turbulence models, i.e., the standard
k–
ɛ model, the RNG
k–
ɛ model, the
k–
ɛ model with Launder and Kato modification and the Realizable
k–
ɛ model were compared in this study. The standard
k–
ɛ model provided inadequate results for the concentration field, because it could not reproduce the basic flow structure, such as the reverse flow on the roof. However, revised
k–
ɛ models provided concentrations in better agreement with the experimental data. The effect of an oblique wind angle and vent locations on the prediction accuracy was also investigated. It was confirmed that the prediction accuracy of the velocity field strongly affected that of the concentration field. The RNG model showed general agreement with the experiment, and was the best of the turbulence models tested. However, it becomes clear that the results for all CFD models show poor prediction accuracy of concentration distribution at the side and leeward surfaces of the building since they all underestimate the concentration diffusion on these regions. The concentrations predicted by all CFD models were less diffusive than those of the experiment.
Computational Wind Engineering is expanding rapidly in the last decade and is expected to be introduced as a design tool for wind-induced loads in future code provisions and standards worldwide. The ...paper discusses the current CWE shortcomings of the state-of-the-art and proposes a methodology that targets to close the current research gaps, from a practical point of view. Monitoring wind tunnel experiments, significant deviations of instantaneous velocity profiles due to high turbulence intensity are expected to be critical for design pressures. This inspired the novel modeling technique - named Dynamic Terrain - that reformulates the turbulence characteristics and assumes that each instantaneous profile is produced by changing the corresponding terrain conditions. Successively derived profiles from the wind tunnel are introduced as inlet conditions in coarse LES computational domain and propagate inside the domain to interact with the building. The incident flow is successfully modelled, in terms of mean, turbulence intensity and spectral content. Mean, standard deviations and peak pressure coefficients correlate well with experimental results and the procedure is advantageous compared to similar computational techniques. The target accuracy is achieved, benefits and limitations of the method are discussed, and conclusions based on experimental and computational observations are drawn.
•Computational evaluation of design wind loads on low rise buildings based on the novel Dynamic Terrain approach•Inflow turbulence modelling with accurate spectral content, mean and turbulence intensity profiles of the incident flow.•Validation of mean, std and peak pressures of experiments from three wind tunnel facilities for open and suburban terrains.•Good agreement of roof peak Cp values of a low-rise building, with straightforward and simple methods.
The paper outlines a set of experimental criteria implemented to examine the influence of geometric scale on wind-induced pressures on roof-mounted solar panels tested in a simulated atmospheric ...boundary layer. The results of this research contribute significantly to the understanding of the obstacles hindering the reliable evaluation of wind loads on solar panels, bearing in mind that the size of wind tunnel models of such structures is a key stumbling block to conducting experiments and getting reliable results. The effect of such shortcomings in the codification process is examined. Three models of geometric ratios 1:50, 1:100 and 1:200 were designed, manufactured and tested in the atmospheric boundary layer wind tunnel of Concordia University. The results show that the geometric test scaling is an important parameter in simulating solar panel models in atmospheric boundary layer wind tunnels, particularly when considering design wind loads.
•Experiments studied the sensitivity of disregarding the geometric test scaling in wind tunnel testing of solar panels.•Relaxing the geometric test scaling of the test solar array models yields discrepancies in mean and peak force coefficients.•Extreme negative and positive net pressure coefficients may vary by a factor of 2 or higher for some critical locations.
The design of rooftop solar panels for wind loads requires provisions to be sufficiently comprehensive to reflect the wind effects on PV module/panel cover plate, individual PV panels, PV panels ...arrays, and their supporting systems. Unfortunately, the focus of the literature studies and the provisions of the current wind codes and standards is on the net pressure coefficients that can be used in the design of PV panel supporting systems. Particularly, current wind codes and standards of practice do not provide design pressure coefficients for elements on cover plates of rooftop PV panels. In this contribution and along with the intention to examine the characteristics of the wind-induced surface pressures, this paper investigates the surface wind loads of a rooftop solar array of eight panels. The tests were carried out in open-terrain exposure at a geometric test scale of 1:50. In preliminary experiments, additional tests were conducted on two more geometric scales, namely 1:100 and 1:200, to assess the effects of the geometric test scale on the experimental pressure coefficients that would be deemed as design loading for the credibility and integrity of the wind tunnel setup established for codification-oriented studies. The experimental results illustrate that applying the design net pressure coefficients of the current wind codes and standards for the design of PV cover plates will lead to significantly undervalued wind loads. On the other hand, it is found that the external pressure coefficients assigned by ASCE/SEI for gable roofs of low-rise buildings with a slope between 7° and 20° are adaptable for the design of elements on cover plates of rooftop PV panels.
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