Effect of local and upwind stratification on flow and dispersion inside and above a bi-dimensional street canyon
Effect of local and upwind stratification on flow and dispersion inside and above a bi-dimensional street canyon
复制标题
DOI：
10.1016/j.buildenv.2019.04.013
复制
发表时间：
2018-11
影响因子：
7.4
通讯作者：
Davide Marucci;M. Carpentieri
中科院分区：
文献类型：
--
作者：
Davide Marucci;M. Carpentieri
本文在风洞中结合壁面温差加热实验研究了稳定分层边界层对二维街道峡谷内流动和弥散的影响。采用激光多普勒风速仪、快速火焰离子化检测器和冷丝风速仪对速度、浓度、温度和通量进行了测量，在等温条件下观察到单涡模式，背风壁加热时也保持单涡模式，但涡速度有相当大的增加。相反，加热迎风壁会产生一个反向旋转的涡流，导致伞内的速度降低。稳定的分层也有助于降低速度，但仅在峡谷的下半部分。湍流动能的最大值被观察到的树冠上方，而在里面，他们集中靠近迎风壁，即使当背风一个被加热。在所有情况下，一个稳定的层结产生了显着的和普遍的湍流减少。迎风加热被发现产生较大的温度增量内的冠层，而在背风的情况下，热量立即腾空冠层上方。一个稳定的接近流降低了温度和热通量。被动示踪剂是从位于地面水平的街道峡谷中心的点源释放的。迎风壁面加热破坏了主涡环流，使迎风面污染物浓度增加，从而影响了烟羽的截面形状。传入的稳定分层的应用程序创建了一个普遍的增量的冠层内的污染物，浓度的两倍大。湍流污染物通量被发现显着只有在屋顶水平和接近源。另一方面，在迎风壁加热的情况下，平均通量的减少，使湍流分量相关的其他locations.The目前的工作突出了边界层分层和局部加热的重要性，都能够在微尺度范围内的流量和污染物字段创建显着的修改。
The effects of a stably-stratified boundary layer on flow and dispersion in a bi-dimensional street canyon with unity aspect ratio have been investigated experimentally in a wind tunnel in combination with differential wall heating. Laser-Doppler anemometry together with a fast flame ionisation detector and cold-wire anemometry were employed to sample velocities, concentration, temperatures and fluxes.A single-vortex pattern was observed in the isothermal case, preserved also when leeward wall was heated, but with a considerable increment of the vortex speed. Heating the windward wall, instead, was found to generate a counter-rotating vortex, resulting in the reduction of velocity within the canopy. The stable stratification also contributes reducing the speed, but only in the lower half of the canyon. The largest values of turbulent kinetic energy were observed above the canopy, while inside they were concentrated close to the windward wall, even when the leeward one was heated. An incoming stable stratification produced a significant and generalised turbulence reduction in all the cases. Windward heating was found to produce larger temperature increments within the canopy, while in the leeward case heat was immediately vacated above the canopy. A stable approaching flow reduced both the temperature and the heat fluxes.A passive tracer was released from a point source located at ground level at the centre of the street canyon. The resulting plume cross-section pattern was mostly affected by the windward wall heating, which produced an increment of the pollutant concentration on the windward side by breaking the main vortex circulation. The application of an incoming stable stratification created a generalised increment of pollutant within the canopy, with concentrations twice as large. Turbulent pollutant fluxes were found significant only at roof level and close to the source. On the other hand, in the windward wall-heated case the reduction of the mean flux renders the turbulent component relevant in other locations as well.The present work highlights the importance of boundary layer stratification and local heating, both capable of creating significant modifications in the flow and pollutant fields at microscale range.