Plume or bubble? Mixed-convection flow regimes and city-scale circulations
Plume or bubble? Mixed-convection flow regimes and city-scale circulations
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DOI：
10.1017/jfm.2020.360
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发表时间：
2020-06
影响因子：
3.7
通讯作者：
H. Omidvar;E. Bou‐Zeid;Qi Li;J. Mellado;P. Klein
中科院分区：
文献类型：
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作者：
H. Omidvar;E. Bou‐Zeid;Qi Li;J. Mellado;P. Klein
城市周围的大尺度环流受到城市热岛和区域风型的共同调制。根据这些变量，环流分为不同的区域，从平流主导(羽流区域)到对流驱动(气泡区域)。利用量纲分析和大涡模拟，研究了这些不同的环流与城市和农村热通量以及上游风速之间的比例关系。有两个无量纲参数可以控制流动的动力学：(1)乡村和城市的热对流速度之比，以对比它们各自的浮力通量；(2)乡村地区的整体流入速度与对流速度之比。最后，利用从乡村到城市过渡区域的垂直流速，建立了将不同的大尺度环流划分为烟羽、气泡或过渡区域的标准。这些发现对城市通风有影响，因为气泡制度预计会捕获污染物，以及对典型混合对流中的标度分析。
Large-scale circulations around a city are co-modulated by the urban heat island and by regional wind patterns. Depending on these variables, the circulations fall into different regimes ranging from advection-dominated (plume regime) to convection-driven (bubble regime). Using dimensional analysis and large-eddy simulations, this study investigates how these different circulations scale with urban and rural heat fluxes, as well as upstream wind speed. Two dimensionless parameters are shown to control the dynamics of the flow: (1) the ratio of rural to urban thermal convective velocities that contrasts their respective buoyancy fluxes and (2) the ratio of bulk inflow velocity to the convection velocity in the rural area. Finally, the vertical flow velocities transecting the rural to urban transitions are used to develop a criterion for categorizing different large-scale circulations into plume, bubble or transitional regimes. The findings have implications for city ventilation since bubble regimes are expected to trap pollutants, as well as for scaling analysis in canonical mixed-convection flows.