Publications

Information on pedestrian-level wind (PLW) speed for wind comfort assessment can be obtained with wind-tunnel measurements or Computational Fluid Dynamics (CFD). Wind-tunnel measurements for PLW are routinely performed with low-cost techniques such as hot-wire or hot-film anemometers, Irwin probes or sand erosion, while Laser-Doppler Anemometry (LDA) and Particle-Image Velocimetry (PIV) are less often used because they are more expensive. CFD simulations are routinely performed by the relatively low-cost steady Reynolds-Averaged Navier-Stokes (RANS) approach. Large-Eddy Simulation (LES) is less often used because of its larger complexity and cost. This paper first briefly addressed wind-tunnel and CFD techniques to determine PLW speed, and some comparative studies that systematically indicate that the low-cost wind-tunnel techniques and steady RANS simulations can provide accurate results (?10%) in high wind speed regions while their accuracy strongly deteriorates in low wind speed regions. Next, it is argued that this does not necessarily compromise the accuracy of PLW comfort assessment, because the higher wind speed regions provide the largest contribution to the discomfort exceedance probability in the comfort criterion. Although LDA, PIV and LES are inherently and potentially more accurate techniques, this paper supports the continued use of faster and cheaper techniques for PLW comfort assessment.

Wind-driven rain is one of the most important boundary conditions for numerical Heat-Air-Moisture (HAM) transfer models. Due to the complexity of WDR however, the current HAM models generally incorporate it in a very simplified way. Recent research has shown that CFD can provide accurate estimates of WDR on building facades. Therefore, in this paper, a combined CFD-HAM approach is presented. It is applied for a simplified wall model. It is shown that the accuracy of the HAM-simulation results is to a large extent determined by the time resolution of the meteorological input data and by the data-averaging technique used for these data. Some guidelines for accurate HAM analyses with WDR are provided.

Computational Fluid Dynamics (CFD) allows researchers and practitioners to analyze cyclist aerodynamics and identify areas for improvement. Despite the numerous CFD simulations of cyclist aerodynamics in the scientific literature, the extent to which user choices in the large number of computational parameters affect the simulation results remains largely unexplored. This paper aims to establish a set of best practice guidelines for CFD simulations of an isolated cyclist in time trial position through a systematic and comprehensive sensitivity analysis. It includes the computational grid in terms of surface, near-wall, and far-field volume grids and the turbulence modeling. The study reveals a high sensitivity of the computed drag area to the surface grid resolution and y+ value, while the impact of the growth rate and the grid resolution in the wake is relatively smaller. The results emphasize the importance of complete reporting of grid characteristics and the need for grid-sensitivity analyses, and provide prioritization of the key parameters for such analyses. Satisfactory agreement with wind tunnel measurements is achieved using Scale-adaptive simulations (SAS) and steady RANS with the Transition SST (T-SST) or SST k-ω turbulence model for closure. This work intends to contribute to accurate and reliable CFD simulations of cycling aerodynamics.

Urban microclimate studies are gaining popularity due to rapid urbanization. Many studies documented that urban microclimate can affect building energy performance, human morbidity and mortality and thermal comfort. Historically, urban microclimate studies were conducted with observational methods such as field measurements. In the last decades, with the advances in computational resources, numerical simulation approaches have become increasingly popular. Nowadays, especially simulations with Computational Fluid Dynamics (CFD) is frequently used to assess urban microclimate. CFD can resolve the transfer of heat and mass and their interaction with individual obstacles such as buildings. Considering the rapid increase in CFD studies of urban microclimate, this paper provides a review of research reported in journal publications on this topic till the end of 2015. The studies are categorized based on the following characteristics: morphology of the urban area (generic versus real) and methodology (with or without validation study). In addition, the studies are categorized by specifying the considered urban settings/locations, simulation equations and models, target parameters and keywords. This review documents the increasing popularity of the research area over the years. Based on the data obtained concerning the urban location, target parameters and keywords, the historical development of the studies is discussed and future perspectives are provided. According to the results, early CFD microclimate studies were conducted for model development and later studies considered CFD approach as a predictive methodology. Later, with the established simulation setups, research efforts shifted to case studies. Recently, an increasing amount of studies focus on urban scale adaptation measures. The review hints a possible change in this trend as the results from CFD simulations can be linked up with different aspects (e.g. economy) and with different scales (e.g. buildings), and thus, CFD can play an important role in transferring urban climate knowledge into engineering and design practice.

An overview of research on rainwater runoff from building facades is presented. Observations, on-site measurements, laboratory measurements and modelling efforts are discussed. While observations are many, on-site experiments and modelling efforts are few and have been almost exclusively made at plain facades without details. To the knowledge of the authors, current hygrothermal models do not yet contain runoff models. Implementation of runoff models is an important requirement for the upcoming 2D and 3D generations of HAM models.<br/><br/>\nUn survol de résultats de recherche sur l'écoulement de l'eau de pluie sur les façades de bâtiment est présenté.\nNous discutons des travaux d'observation, de mesure en laboratoire, et par simulation sur ordinateur. Alors\nque les observations in situ sont nombreuses, il y a peu de travaux expérimentaux ou de modélisation, et ce\nseulement pour des façades tout à fait planes. Aussi, à notre connaissance, les outils actuels de modélisation\nhygrothermique ne tiennent pas compte de l’écoulement de l'eau de pluie. Le développement et\nl'implémentation de modèles d'écoulement de l'eau de pluie est une spécification cruciale pour les prochaines\ngénérations de modèles hygrothermiques, en deux ou trois dimensions.