A wind tunnel study on three-dimensional buoyant flows in street canyons with different roof shapes and building lengths

Abstract

Higher temperatures are measured in urban areas compared to surrounding rural areas due to the urban heat island effect. One of the most efficient ways of removing heat from urban areas is wind-driven ventilation. Building configurations have a strong impact on the wind flow patterns and therefore on the heat removal from urban areas. Buoyancy can promote heat removal by inducing three-dimensional flow structures. This prevents the formation of standing vortices in street canyons, which are formed for forced convective flow regimes and trap heat inside the street canyons. A wind tunnel study is conducted for street canyons in an urban area. The wind tunnel floor is heated to different temperatures to induce buoyancy. The flow structures are measured with PIV (Particle Image Velocimetry) on horizontal and vertical planes within the street canyon and the air temperatures are measured with an approach based on infrared thermography. The flows entering the street canyon through the lateral sides are measured on a horizontal PIV plane. These lateral flows can be found for buoyancy driven flows and are important, since they prevent the formation of standing vortices. To improve the heat removal in forced convective flows, different roof shapes and heights are studied and the lengths of the street canyon buildings are varied. The results show that lateral flows can be found for street canyons with non-uniform building heights and that the air temperatures are decreased in such street canyons due to the improved ventilation.