兩層樓建築物橫流型自然通風模式的CFD研究：植栽風擋設置距離與孔隙率的效應比較

CFD Study on Cross Natural Ventilation of a Two-Storey Building: Comparison of Effects of Hedgy Windbreaks with Different Placing Distances and Porosit

本研究對配置於低層建築物前迎風面的植栽風擋進行量化的探討，藉由計算流體力學的分析方法，來預測風擋設置距離與孔隙率變化所導致之建築物周圍與室內流體運動的改變，以了解植栽風擋對低層建築物橫流型通風的影響。研究結果顯示，植栽風擋會影響經過的氣流結構，進而改變了風擋後建築物室內外的通風型態。本研究歸納出三種典型的氣流模式，分別為「穿越流」、「停滯流」，以及「循環流」。就通風目的而言，風擋的孔隙率過低將會導致空氣循環、停滯，甚至產生零通氣量的現象，而植栽圍籬太靠近建築物則無法為二樓室內空間提供有效的遮擋強風效果。

The effects of placing hedgy windbreaks ahead of a building on the airflow in and around the building are examined numerically. A CFD simulation is carried out to predict the fluid flow characteristics around the porous hedge and the building resulted from different placing distances and hedge porosities. Results show that the porous hedge could modify the flow structures behind the hedge, and thus alter the cross ventilation in the building. Three typical flow patterns behind the porous hedge are identified: the penetrating flow, the stagnant flow and the recirculating flow in the study. It is further found that there exists a critical hedge porosity below which the cross ventilation in the building is inverse. From the viewpoint of ventilation, it is suggested to avoiding using hedgy windbreaks with hedge porosities near critical value. It is also found that the porous hedge will not effectively reduce airflow speed in the second floor when placing close to the building.