Large‐eddy simulation of the cross-ventilation behavior in an array of low‐rise buildings

In this paper, the relation between natural ventilation behavior and building separation within urban canyon geometry is examined to study the indoor ventilation performance with respect to street canyon density. Computational fluid dynamics (CFD) of large‐eddy simulation (LES) with the one equation subgrid‐scale (SGS) model was performed on an array of two‐dimensional (2D) hypothetical low-rise buildings by the open‐source CFD code OpenFOAM. Three LESs of different separation-to-building-width ratios, which covered different flow regimes inside the canyon, were simulated. The CFD results revealed that for dense street canyons, for instance, when the separation-to-building-width ratio was one, the prevalent wind flow could hardly reach the ground level. Reversed flow was dominant near the ground and within the building envelope. As the separation was increased, changes in the flow pattern such as the positions, the sizes and the intensities of the recirculations could be observed. Furthermore, the contribution of turbulence to the total ventilation rate differed by various extents. When the ratio approached one and a half, the mean ventilation flux across the building envelope dropped to around zero. Whereas the turbulent air flux dominated the ventilation that fluctuated around 15% of the roof-level mean flow. The effects of the turbulence scales on natural ventilation were also studied. On the windward side, larger scale fluctuations were observed.