The impact of urban parameters on the ventilation in idealized urban model with fixed area

Abstract

With population growing rapidly, the lack of land is becoming serious. In order to make full use of land, more and more buildings are built in a limited area and the building height is higher and higher. However, the change of the building height and building density has the significant impact on the efficiency of the urban ventilation. This papers investigates canyon ventilation under neutral atmosphere condition with same building area density (λp = 0.25) and fixe ground area (300mX300m) but various frontal building area density (λf = 0.075∼0.425), plot ratio (λr = 2.52∼4.00). The roof air change rate per hour (ACHroof) induced by turbulence and the horizontal air change rate per hour (ACHhorizontal) induced by mean flow, calculated by the CFD simulation by standard k-ϵ model, is adopt to quantify the vertical and horizontal air exchange, respectively. The results show that: 1) with the increase of the frontal building area density (λf ), ACHroof increases logarithmically and ACHhorizontal decays exponentially. With the increase of λf, the resistance of buildings to airflow increases gradually, this is why the ACHhorizontal decreases exponentially, the remaining air flow is discharged through the roof, so ACHroof increases logarithmically, but the sum of ACHhorizontal and ACHroof is constant, equal to 10.2h -1. 3) ACHhorizontal is negatively correlated with plot ratio, while ACHroof is positively correlated with plot ratio. This is because plot ratio represents the building density, drag force increases with building density. This study can be used to guide urban planning and improve urban ventilation environment.