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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.

Highlights • A general design framework is developed for improving low pedestrian level wind environment. • The improvement measures and evaluation criteria in current studies are reviewed and summarized. • A university campus is used as case study to demonstrate the design framework. • The outcomes of this paper can assist policy-makers to establish sustainable urban planning policies., An acceptable pedestrian level wind environment is essential to maintain an enjoyable outdoor space for city residents. Low wind velocity environment can lead to uncomfortable outdoor thermal experience in hot and humid summer, and it is unable to remove the pollutants out of city canyons. However, the average wind velocity at pedestrian level is significantly lowered by closely spaced tall buildings in modern megacities. To improve the low wind velocity environment at pedestrian level in high-density cities, a general framework and detailed guidelines are needed. This study is the first time to develop such a framework, and provide detailed guidelines for improving pedestrian level low wind velocity environment in high-density cities. Additionally, a detailed review and summarisation of evaluation criteria and improvement measures are presented in this paper, which provide additional options for urban planners. To investigate the performance of the framework, the Hong Kong Polytechnic University campus was utilised as a case study. Results showed that pedestrian level wind comfort was greatly improved with the developed framework. The outcomes of this study can assist city planners to improve the low wind velocity environment, and can help policy makers to establish sustainable urban planning policies.

Improvements for the pedestrian level wind environment and outdoor thermal comfort have become increasingly important in urban planning in light of concerns about global warming and urban heat island effects. Therefore, the goal of this study is to determine the optimum wind environment and outdoor thermal comfort for an ideal urban canyon in which the buildings have lift-up designs. A multi-stage optimization method is proposed consisting of three stages for the optimization process, e.g., surrogate model development, multi-objective optimization, and decision-making. An area weighted wind velocity parameter ( M V R ¯ ) and an outdoor thermal comfort parameter ( P E T ¯ ) are chosen as the design objectives, and four design variables are selected. The response surface methodology combining computational fluid dynamics simulation results are used to fit surrogate models. The non-dominated sorting genetic algorithm is employed to find Pareto optimal solutions, and three decision-making strategies are adopted to determine the final optimum design solution in parallel. The optimization process of the ideal urban canyon confirms that the proposed method is highly effective to determine optimum building design in urban areas. The findings in this study are valuable for city-planners and policy-makers to build a sustainable urban living environment.