T. Stathopoulos

Application of computational fluid dynamics in building performance simulation for the outdoor environment: an overview

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.

Computational wind engineering : Past achievements and future challenges

The paper reviews the current state of the art in computational wind engineering, particularly as it relates to applications of numerical flow modelling for the evaluation of wind effects on buildings and their environment. The variability of computational results is presented and compared with that of wind tunnel measurements. Concerns are expressed regarding the current application of the numerical approach in the design practice in cases for which the computational results may not be adequate. Future challenges regarding the improvement of computational wind engineering methodologies are discussed and the importance of identifying resolution and numerical errors is emphasized.

Microclimate and Downtown Open Space Activity

Microclimatic conditions in business district open spaces tend to be more extreme than prevailing weather conditions. Although the buildings are chiefly responsible for this inclemency, their shapes and arrangement could also potentially be used to moderate or enhance prevailing conditions. To provide better guidance in design, we need to know how humans respond to microclimatic conditions. In particular, we need to know first how sunlight, temperature, humidity, and wind combine in sensations of outdoor human comfort, and second, how important microclimatic factors are in behavior. This article reports on a study of revealed preferences for certain local climatic conditions, measured in terms of presence levels and activities in seven closely spaced corporate plazas and public squares in a built-up, downtown area. The observations were conducted over a 5-month period. The measured microclimatic conditions accounted for most of the variance in activity levels and types. Temperature was the single most important variable. Although great variation in level of use among spaces cannot be explained solely in terms of microclimatic differences, use within spaces varies chiefly as a function of microclimate.

Wind-induced interference effects on buildings - a review of the state-of-the-art

The evaluation of wind loads on buildings is carried out mainly by using codes and standards, whose specifications are generally based on wind tunnel tests performed on isolated structures in an open terrain. However, it has been shown by several researchers that wind loads on buildings in realistic environments may be considerably different from those measured on isolated buildings. Neighbouring structures may either decrease or increase the flow-induced forces on a building, depending mainly on the geometry and arrangement of these structures, their orientation with respect to the direction of flow and upstream terrain conditions. Therefore, this effect, commonly known as interference, must be properly assessed by designers and planners. This paper reviews and analyzes over six decades of work pertaining to interference effects. In addition to highlighting the seriousness of the problem, the analysis has found inconsistencies in the results and incoherence among various studies. A few attempts to provide general recommendations have not been successful, due to the complex nature of the problem and the large variation among various studies. It is, therefore, imperative to tackle the problem of interference in a systematic manner in order to propose a generalized set of guidelines that will be of practical use to building designers and planners.

Wind Driven Flow through Openings – A Review of Discharge Coefficients

Abstract This paper reviews the current literature on discharge coefficients (CD) of openings and compares different studies for wind-driven cross-ventilation. Considerable variation of discharge coefficients with opening porosity, configuration (shape and location in the façade), wind angle and Reynolds number is shown. Consequently, the use of a constant CD value such as that given in textbooks or other sources might be an invalid simplification. Scaling, upstream flow conditions, internal partitions and the assumptions of turbulent flow, sealed body and energy dissipation made for the application of the orifice equation should be considered in wind tunnel experiments of cross-ventilation.

Computer simulation of wind environmental conditions around buildings

Mean wind environmental conditions around buildings necessary for the assessment of pedestrian comfort, dispersion of pollutants, as well as snow and dust transport have been evaluated numerically. Modified Navier-Stokes equations and k-e turbulence models used in the simulation are discretized by the control volume method. The SIMPLE algorithm is applied to fulfill the condition of continuity. A non-uniform staggered grid arrangement containing 235,000 nodes is utilized for the three-dimensional numerical modelling. A typical Montreal location near the downtown campus of Concordia University has been selected as a test case for the computation. Validation of the computed results has been carried out by using data from experiments conducted in the boundary layer wind-tunnel of the Centre for Building Studies at Concordia University. Computed and measured data indicate that the most significant features of the wind environmental conditions around buildings can be predicted with reasonable accuracy. The advantages and drawbacks of computer simulation are discussed in the paper.

An experimental approach to the economical measurement of spatially-averaged wind loads

Abstract A pneumatic manifolding technique is suggested as an economical means for evaluating time-varying spatially-averaged pressure loads on tributary areas of design interest on building models. Results of some exploratory experiments are presented which show that mean and r.m.s. pressures can be determined accurately by such manifolds. Furthermore, the frequency response of the devices tested is virtually flat over the range for which the frequency response of the component tubes is flat, and shows little non-linearity. A pseudo-amplification of high frequency information takes place due to the finite grid of pressure taps; however, in practice this is shown to occur above much of the response range of interest, and to be correctable analytically.

Numerical evaluation of wind-induced dispersion of pollutants around a building

Abstract Wind flow perturbations, recirculations and turbulence generated by buildings often dominate air pollutant distributions around buildings; this may be a great concern for engineers, architects and health professionals. The paper refers to an attempt to evaluate the air pollutant distribution around a building by solving the concentration equation based on the previously simulated wind flow field. The paper shows the application of the hybrid scheme for the evaluation of pollutant concentration around a rectangular building for two different sources under conditions of neutral atmospheric stratification. Results have been compared to the available experimental data from previous studies in boundary layer wind tunnels. Data agree well far downwind of the building but agree less satisfactorily close to the wall and within the wake zone.

Wind environmental conditions in passages between buildings

Experimental measurements have been carried out in a boundary layer wind tunnel to determine wind velocity and turbulence conditions in a passage between two rectangular buildings. The experiments were done under simulated open country terrain conditions for a wide range of wind azimuths. Geometrical parameters included the height of two buildings and the passage width. Results show that the most critical wind velocity conditions occur for buildings of different heights and at a point near the passage entrance for a wind direction skewed by 30° from the passage centre line. Turbulence conditions, however, are found more critical for wind perpendicular to the passage centre line. Also, the larger the passage width, the lower the velocity amplifications and the higher the turbulence intensities in the passage. The paper demonstrates that different K parameters for the inclusion of wind gustiness in an equivalent effective wind speed make little difference in the comfort criteria evaluation.

Wind loads on low-rise buildings: a review of the state of the art

Abstract This paper refers to the most recent research on wind loads on low-rise buildings. Novel measurement techniques and methodologies are reviewed, and selected experimental results from various studies are presented. Particular emphasis is given to works aimed at the formulation of codified data, i.e. results appropriate for incorporation into design standards and codes of practice. Only either full-scale studies or those done under conditions simulating the earths atmospheric boundary layer have been considered. Comparisons between full-scale and laboratory results are discussed. Areas requiring additional research and analysis are identified.