Fluid dynamic and heat transfer parameters in an urban canyon S. Bottillo ⇑ , A. De Lieto Vollaro, G. Galli, A. Vallati Sapienza University of Rome – DIAEE – Via Eudossiana 18, 00184 Rome, Italy Received 28 June 2013; received in revised form 22 October 2013; accepted 24 October 2013 Available online 22 November 2013 Communicated by: Associate Editor Matheos Santamouris Abstract A microclimatic analysis in a typical urban configuration, has been carried out. Using a CFD method, a N-S oriented urban street canyon, with a given H/W ratio, has been examined. The standard k–e turbulence model has been used to simulate a three-dimensional flow field and to calculate the thermo-fluid dynamics parameters that characterize the street canyon. The aim of this study is to inves- tigate the effect of solar radiation on the flow field and thermal parameters within the canyon. A comparison between transient and sta- tionary simulations has been performed to evaluate the importance of considering the thermal inertia effects in an urban street canyon study. The dynamic characteristics of the 3D flow in the canyon have been compared with other numerical simulations and experimental results. Furthermore a thermo-fluid dynamic analysis of natural convection effects on the heat transfer coefficient and turbulent kinetic energy, has been carried out. Ó 2013 Elsevier Ltd. All rights reserved. Keywords: Urban microclimate; Urban canyon; CFD; Solar radiation 1. Introduction The landscape of dense urban areas can be described by units of street delimited by two continuous rows of build- ings to form a “canyon”. This geometry is often described by a single parameter, the canyon aspect ratio (H/W), which is defined as the ratio of the building height (H) to the width between buildings (W). As to the incoming solar radiation and the heating of canyon surfaces, the orienta- tion of the canyon relative to the solar path is also critical in determining the timing and extent to which surfaces receive direct sunlight. Several studies have been performed on different street canyons (Takebayashi and Moriyama, 2012; Bozonnet et al., 2005; Lei et al., 2012; Xie et al., 2007). An experimental validation of a 3D numerical sim- ulation has been performed by Assimakopoulos et al. (2006); they performed tests using a numerical model on a grid of buildings. By numerical tests characterized by a 2D spatial domain and with assigned surfaces tempera- tures, Lei et al. (2012) studied the impact of ground heating on the flow fields in a street canyons, Xie et al. (2007) stud- ied the effects of fac ßades and ground heating on the pollu- tant dispersion, Saneinejad et al. (2011) investigated on the heat transfer coefficient in a street canyon, simulated as a cavity, using the low-Reynolds number modeling; they found a strong influence of thermal effect on the flow field. Allegrini et al. (2012a) analyzed the convective heat trans- fer at building fac ßades in several urban configurations, using the adaptive wall function approach developed by Defraeye et al. (2011) and Allegrini et al. (2012b); they con- cluded that the AWF provides more accurate heat transfer analysis in urban CFD studies. Offerle et al. (2007) used wind and temperature measurements to examine the ther- mal structure within a street canyon. They found that buoyancy effects were not seen to have as large an impact on the measured flow field as has been shown in the numer- ical experiments. Kovar-Panskus et al. (2002) performed a 0038-092X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.solener.2013.10.031 ⇑ Corresponding author. Tel.: +39 06 44 58 56 64; fax: +39 06 48 80 120. E-mail address: simone.bottillo@uniroma1.it (S. Bottillo). www.elsevier.com/locate/solener Available online at www.sciencedirect.com ScienceDirect Solar Energy 99 (2014) 1–10