Abstract Wind-driven dynamic force and buoyancy force are two main driving forces in urban ventilation. As a novelty, this paper performs scaled outdoor measurements to examine the relative role of these two driving forces by non-dimensional buoyancy parameter B within two-dimensional (2D) street canyons in SOMUCH (Scaled Outdoor Measurement of Urban Climate and Health). Four aspect ratios (building height/street width, H/W = 1, 2, 3, 6; H = 1.2 m) were considered to mimic different morphologies. The temperature difference between east and west walls ( Δ T e a s t − w e s t ) was emphasized to reveal the flow characteristics affected by such thermal effects. The results show that the wall temperature varies with street-wall orientation. Δ T e a s t − w e s t becomes negative in the morning but positive in the afternoon, and maximum | Δ T e a s t − w e s t | could reach 12.7 °C. Street aspect ratio largely determines the thermal structure and flow characteristics inside street canyons. As aspect ratio increases, Δ T e a s t − w e s t and normalized horizontal velocity U 0.25 H / U 2 H (i.e. ratio of horizontal velocity at height of z = 0.25H to that at z = 2H) decrease. Besides, two flow regimes are observed: For H/W = 1, 2, 3, U 0.25 H / U 2 H is approximately constant (i.e. 0.26, 0.17, 0.12) when B Bc (i.e. buoyancy force cannot be negligible), U 0.25 H / U 2 H rises non-linearly with B, and such increase is faster as H/W = 2, 3 than H/W = 1. It indicates that narrower streets attain more evident impact of buoyancy effect on street ventilation. Overall, this study directly investigates the influence of solar heating on turbulent flow and provides high-quality experimental data for validation of further numerical simulations.

中文翻译：

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将重新提交至 2020 年建筑与环境 长宽比和太阳能加热对二维街道峡谷中流动和通风的影响，通过缩放室外实验

摘要 风驱动动力和浮力是城市通风的两个主要驱动力。作为一个新颖之处，本文通过 SOMUCH（城市气候和健康的缩放室外测量）中二维 (2D) 街道峡谷内的无量纲浮力参数 B 进行了缩放室外测量，以检查这两种驱动力的相对作用。四种纵横比（建筑高度/街道宽度，H/W = 1, 2, 3, 6；H = 1.2 m）被认为是模拟不同的形态。东西壁之间的温差（ΔT东-西）被强调以揭示受这种热效应影响的流动特性。结果表明，墙温随街墙方向而变化。Δ T 东 - 西在上午变为负值，而在下午变为正值，和最大| Δ T 东 - 西 | 最高可达 12.7 °C。街道纵横比在很大程度上决定了街道峡谷内的热结构和流动特性。随着纵横比的增加，ΔT东-西和归一化的水平速度U 0.25 H / U 2 H（即z = 0.25H高度处的水平速度与z = 2H处的水平速度之比）减小。此外，观察到两种流态：对于 H/W = 1, 2, 3, U 0.25 H / U 2 H 近似恒定（即 0.26, 0.17, 0.12），当 B Bc（即浮力不可忽略）时，U 0.25 H / U 2 H随B呈非线性上升，H/W = 2, 3上升速度比H/W = 1快。说明街道越窄，浮力效应对街道通风的影响越明显。全面的，