Towards developing an idealised city model with realistic aerodynamic features

E. Reda; R. Zulkifli; Z. Harun

doi:10.15282/jmes.11.4.2017.2.0268

Authors

E. Reda Department of Mechanical Engineering, Alexandria University, Alexandria, Egypt
R. Zulkifli Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, UKM Bangi, 43600, Selangor, Malaysia
Z. Harun Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, UKM Bangi, 43600, Selangor, Malaysia

DOI:

https://doi.org/10.15282/jmes.11.4.2017.2.0268

Keywords:

CFD, LES, Air flow, Actual city, Idealised model, Uneven building layout

Abstract

Many concerns related to natural ventilation in urban areas have been deduced from experimental or computational fluid dynamics simulations on idealised models. However, it is not definite that the flow through these idealised models presents similar characteristics to actual urban areas. The objective of this research is to suggest an approach to close the gap between idealised models and genuine cities; i.e., predict actual urban flow characteristics from the ready data of idealised models. The flow was simulated by large-eddy simulation through both the actual city model and a group of idealised models of different structures but the same average dimensions and buildingpacking-density as the actual city. The numerical setup was validated by comparison with wind tunnel measurements from the literature. It was found that an equivalent to the average velocity profile throughout an idealised model can be achieved by a mix of the “five-point spatial average” and the “four-point spatial average”. The vertical profiles of mean and turbulent windward velocities of the idealised models manifest a general similarity to those of the actual model. On the other hand, the cross-wind and wall-normal components show large discrepancies. In all cases, the idealised models exhibit very narrow atmospheric surface layer heights compared to the actual model. IM-RAN (which represents a structure of semi-random configuration) displayed the closest results to the actual model but condensed in half the actual model surface layer height. A correction formula was devised to close the gap between the two models. The results confirm the ability to utilise idealised models to deliver recommendations regarding urban environment planning; though, attention should be paid to the selection of the idealised model and corrections may be needed.

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