Urban microclimate analysis of a real compact urban area: CFD and on-site measurements

Because of the rapid trend toward urbanization around 54% of the world’s population currently live in urban areas (UNFPA, 2007). The urbanized population is projected to increase and reach up to 66% by 2050 (United Nations, 2014). In addition, due to climatic changes phenomena like the Urban Heat Island (UHI) effect and heat waves are becoming more severe, with dramatic consequences for the urban population (Toparlar et al., 2015; Montazeri et al., 2017). Considering this trend, problems related to urban overpopulation are expected to get more intense in the next years, hence in this perspective, the analysis of microclimatic conditions in urban areas is getting more significant. Through the detailed literature review, it appears that most of the studies focusing on the analysis of microclimatic conditions use observational approaches such as on-site measurements, since this method provides information about the real complexity of the microclimatic conditions in urban areas, without any similarity issues. While computational power is radically increasing, the use of numerical simulation approaches is getting more popular. Most of the numerical studies use the Energy Balance Model which is based on the law of energy conservation. However, the use of Computational Fluid Dynamics (CFD) is considered advantageous since it can provide information of both temperature and velocity fields, and can be used in higher resolution scales. In this perspective, this study analyzes microclimatic conditions in a real compact urban area, with the use of CFD simulations, and results are compared with on-site measurements of the same area. The real compact inhomogeneous urban area under study is located in Nicosia old town, in Cyprus. High-resolution Computational Fluid Dynamics (CFD) simulations are performed based on the 3D unsteady Reynolds-Averaged Navier-Stokes equations to assess the air temperature and wind speed distributions. The on-site measurements took place as a part of the European funded project with code name TOPEUM (Neophytou et al., 2011), with collected data of air and surface temperature. The results show that CFD can predict air temperatures in compact real urban areas, with an average deviation of 6.8%, and surface temperatures with average deviation of approximately 6 to 7%. Based on the results, conclusions are going to be made regarding thermal comfort in the case study area.