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Large eddy simulation (LES) is increasingly recognized as an important approach in the assessment of pedestrian level wind (PLW) conditions, while its numerical performance is sensitive to a few key parameter settings. This study aims to further identify the sensitivities to these main influencing parameters in modeling wind flow around a building array using LES. This is achieved by quantitatively comparing mean wind velocities from the LES predictions and those from a benchmark wind tunnel experiment. The parameters investigated are the mesh resolution, discretization time step and sampling period, vortices’ number of the inlet flow, the upstream distance of the computational domain, and the sub-grid scale (SGS) models. Results are quantified using four validation indices. Specifically, the correlation coefficient R between the predicted results using SGS model with the dynamic Smagorinsky-Lilly method and the experimental results is 0.89, which is higher than those between the experiment results and other three SGS models. Based on the sensitivity tests, it is recommended that the normalized discretization time step be set below 0.09, and that the normalized sampling period and vortices’ number be above 219 and 190, respectively, in the LES simulation of PLW flows around a building array.

Comfortable and healthy outdoor microclimates are beneficial to sustainable urban development. Based on a comprehensive comparison of some currently frequently used thermal comfort indices, including PMV, WBGT, PET, SET*, and UTCI, the differences among these indices are significant in dealing with the fundamental energy balance model, descriptive equations, and application boundary conditions. In order to validate these indices, a subjective questionnaire survey with field measurements was carried out on a university campus in Guangzhou in southern China. Results revealed strong linear relationships between operative temperature and mean radiant temperature (Tmrt), WBGT, PET, SET*, UTCI, as well as PMV. However, the relationships between these thermal comfort indices and the mean thermal sensation vote (MTSV) are not clear for a hot outdoor environment, especially when the operative temperature was above 34 °C. The ranges of the heat stress category and PMV need to be modified for the evaluation of hot outdoor environments.

Local air circulation is influenced by the drag forces exerted by urban vegetation. In this study, tree canopy parameterization in computational fluid dynamics (CFD) with source term modifications is conducted at the tree scale, which builds upon the models previously used in the literature. A simplified three-dimensional model representing tree canopies is resolved and validated against available wind tunnel experiment. The prediction of turbulence kinetic energy (TKE) is shown to be highly sensitive to the model coefficients in the source term of turbulence dissipation rate (TDR). No optimal set of the model coefficients in the TDR source term can be identified. However, C e 4 > C e5 is found to better reproduce the turbulent quantities behind the canopy than C e4 = C e5 . The reduction of C e 5 value from 1.5 to 0.4 yields a higher TDR source term level by one order of magnitude. The prediction of the mean velocity is primarily controlled by the form drag coefficient, which is heavily correlated to all source terms and their components. Results indicate the feasibility of using a more straightforward modification method in the vegetated microclimate simulations by only adding momentum source terms.

This study conducted simultaneous physical measurements and questionnaire surveys to study the outdoor thermal comfort in the subtropical, high-density Hong Kong. With an innovative analysis method, the study reveals that mean radiant temperature (Tmrt), sun and wind desirability, and wind speed (v) were the top three factors influencing the surveyed thermal sensation vote (TSV), which was not well estimated by the Universal Thermal Climate Index (UTCI); and that UTCI underestimated the effects of v and Tmrt at higher air temperatures (Ta) but overestimated the impacts of Ta and relative humidity on TSV of subjects in Hong Kong. Accordingly, a combined sun and wind condition index (SWI) was defined to explore the combined effects of Tmrt and v on thermal comfort. Within the meteorological parameter ranges of 12.0 ≤ Tmrt ≤ 64.0 ℃, 0 26.0 ℃ and Ta ≤ 26.0 ℃, respectively. A v-Tmrt diagram was thus constructed to indicate the comfort zones of sun and wind combinations, which can be used to estimate the comfort levels of outdoor space in the design stage.