Abstract
Air pollution remains a major health concern in urban areas, where building density and layout strongly influence airflow and natural ventilation. While many studies focus on pollutant concentrations and emission sources, fewer examine how building geometry affects the formation of low-velocity zones. This study investigates the influence of building shape and arrangement on ventilation efficiency using two-dimensional numerical modelling. The incompressible Navier–Stokes equations are solved in Python using the projection method on uniform finite-difference grids. Before analysing the main residential layouts, a test case was performed for two identical domains. In the second domain, the square buildings were rotated by 45°. The results showed that building orientation changes both peak velocity and the extent of low-velocity regions. Three residential configurations were then examined. Case 1 included L-shaped and rectangular buildings on a 501×501 grid, Case 2 contained only rectangular buildings on the same grid, and Case 3 included diamond-shaped and square buildings on a 301×301 grid. Case 2 showed the smallest low-velocity area (11.1%) and the highest mean air velocity (1.101 m/s), corresponding to a 45% reduction in low-velocity area and a 48% increase in mean velocity compared with Case 1 (20.2%, 0.745 m/s). In Case 3, the diagonal orientation caused local flow acceleration, but the low-velocity fraction remained high at 20.6%. Overall, the results show that building arrangement has a strong effect on horizontal airflow distribution. They also indicate that peak velocity alone is not sufficient to assess ventilation quality. The proposed two-dimensional approach can therefore be used as an initial screening tool for comparing alternative residential layouts before more detailed three-dimensional simulations are carried out.