[论文解读] Impact of street canyon morphology on heat and fluid flow-an experimental water tunnel study using simultaneous PIV-LIF technique

Yunpeng Xue, Yongling Zhao+3 more|arXiv (Cornell University)|Jun 8, 2023

Wind and Air Flow Studies参考文献 44被引用 1

一句话总结

本研究利用大型水洞实验，结合同步的粒子图像测速法（PIV）与激光诱导荧光法（LIF），以高分辨率测量了街道峡谷中速度场与温度场，探究了峡谷形态对热量与流体流动的影响。结果表明，峡谷高宽比对通风率（0.02–1.5）与热通量具有决定性影响，局部理查森数能准确描述屋顶处浮力引起的热去除过程。

ABSTRACT

Urban areas are known for their complex atmospheric environments, with the building morphology having a significant impact on local climate patterns, air quality, and overall urban microclimate. Understanding the heat transport and fluid flow in complex urban environments is crucial for improving urban climate resilience, which remains an open frontier in the field of urban studies. To gain a more profound insight into the physical processes occurring in urban areas, particularly within street canyons, we conducted an experimental investigation in a large-scale water tunnel. This study involved the simultaneous examination of heat and flow fields, carried out at high spatial and temporal resolutions, utilizing Laser-induced Fluorescence (LIF) for heat analysis and Particle Image Velocimetry (PIV) for flow analysis. Our results of heat and flow in different street canyons indicate that the flow is significantly influenced by a combination of factors, including canyon configuration, the presence of buoyant force, and the magnitude of the approaching flow. The ventilation rate and heat flux from the street canyon, which are key factors shaping the urban microclimate, are found dominated significantly by the street canyon morphology. For instance, changing the aspect ratio of a street canyon results in a significant change of air ventilation rate, ranging from as low as 0.02 to as high as 1.5 under the same flow conditions. Additionally, canyons with high air ventilation rates exhibit significant heat flux removal at the canyon roof level, which is accurately described by the local Richardson number.

研究动机与目标

• 理解城市街道峡谷形态如何影响复杂城市微气候中的流体流动与热量输送。
• 填补在街道峡谷内浮性流中对速度场与温度场进行高分辨率同步测量的研究空白。
• 量化峡谷高宽比、浮力及来流条件对空气通风率与热通量的影响。
• 验证局部理查森数在描述峡谷屋顶处热通量去除过程中的作用。
• 为改进城市气候建模与可持续城市设计提供实验数据。

提出的方法

• 在大型封闭循环水洞中开展实验，以在受控热力与流动条件下模拟城市街道峡谷流。
• 采用同步的粒子图像测速法（PIV）进行高分辨率二维速度场测量，以及激光诱导荧光法（LIF）进行温度场重建。
• 使用三维参数化城市模型，模拟新加坡的城市形态，以代表真实的建筑布局。
• 改变峡谷高宽比（高宽比），并施加底部加热以产生热浮力力。
• 以高空间与时间分辨率测量流动与热力场，以捕捉复杂的涡旋结构与热分层现象。
• 计算局部理查森数，以关联浮力效应与峡谷屋顶处的热通量。

实验结果

研究问题

• RQ1 在存在热浮力的条件下，街道峡谷高宽比如何影响空气通风率与流场结构？
• RQ2 与中性流条件相比，浮力力在多大程度上改变了街道峡谷中的速度场与温度场？
• RQ3 峡谷形态如何影响屋顶处的热通量去除？这一过程能否通过局部理查森数进行量化？
• RQ4 在三维城市街道峡谷中，流场结构、通风效率与热分层之间存在何种关系？
• RQ5 与点传感器相比，同步PIV-LIF测量在提升热场与流场表征的分辨率与准确性方面有何优势？

主要发现

• 峡谷高宽比显著改变空气通风率，在相同流动条件下，通风率范围从最低0.02到最高1.5不等。
• 高通风率的峡谷在屋顶处表现出强烈的热通量去除，表明热耗散效率高。
• 局部理查森数能有效描述峡谷屋顶处热通量的大小与分布，将浮力效应与热传输联系起来。
• 浮力力显著改变流场结构，包括角落涡与马蹄形涡的形成，尤其在低高宽比峡谷中更为明显。
• 同步PIV-LIF测量揭示了详细且高分辨率的流场与热力场，清晰展现了几何形态、浮力与流动动力学之间的复杂相互作用。
• 本研究证明，形态设计——尤其是高宽比——在控制通风与热去除方面起主导作用，是塑造城市微气候的关键因素。