Time-resolved measurement and simulation of local scale turbulent urban flow
Time-resolved measurement and simulation of local scale turbulent urban flow
复制标题
局部尺度城市湍流的时间分辨测量与模拟
DOI：
10.3929/ethz-a-010657618
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发表时间：
2016
影响因子：
2.6
通讯作者：
M. Immer
中科院分区：
文献类型：
--
作者：
M. Immer
随着城市化的持续发展和人口规模的不断增加，对城市微气候的了解变得更加重要。城市微气候是建筑物之间和建筑物上方的特定气候条件，包括风速、气温、湿度和污染物浓度。这些条件可能因城市形态而异。当地的小气候对建筑能源需求、行人风舒适度和居民健康有影响。本研究旨在提高对局部尺度城市流场的理解。具体来说，研究了街道峡谷上方流动中存在的湍流对街道峡谷顶部剪切层行为的影响。由于湍流的不稳定性质，采用了时间分辨技术。使用时间分辨立体粒子图像测速 (PIV) 系统在 ETHZ/EMPA 大气边界层 (ABL) 风洞中进行风洞测量，并使用时间分辨大涡模拟 (LES) 在 EMPA 和 ETHZ 的高性能计算 (HPC) 设施上进行流动模拟。风洞实验通过使用专门构建的风洞装置，模拟了单位纵横比街道峡谷几何形状的大范围湍流条件。使用分层地板设置和产生湍流的尖顶和障碍物来改变湍流程度。时间分辨立体 PIV 数据用于对选定的腔体流动进行详细研究。使用 Q 准则的涡核时空可视化叠加在扫掠和喷射事件上。这为剪切层动力学以及与外部湍流的相互作用提供了有用的见解。研究发现，中度湍流的情况具有剪切层，通过开尔文-亥姆霍兹不稳定性产生涡流，而高湍流的情况则显示出由扫掠事件引起的上游边缘的涡流脱落。对高度湍流情况的时间相关分析表明，间歇性的大规模扫掠事件会渗透到空腔中。使用 LES 进行流动模拟，以研究单位纵横比街道峡谷的湍流。对于入口边界con-
With continuing urbanization and increasing population size, the understanding of the urban microclimate becomes more important. The urban microclimate is the specific climatic conditions found between and above buildings, meaning wind speed, air temperature, humidity and pollutant concentrations. These conditions can vary locally based on the urban morphology. The local microclimate has an influence on the building energy demand, pedestrian wind comfort and health of the inhabitants. This research aimed to improve the understanding of the local scale urban flow field. Specifically, the influence of turbulence present in the flow above street canyons on the behaviour of shear layers at the street canyon top was studied. Due to the instationary nature of turbulent flows, time resolved techniques were employed. Wind tunnel measurements were conducted in the ETHZ/EMPA Atmospheric Boundary Layer (ABL) wind tunnel using a time resolved stereoscopic Particle Image Velocimetry (PIV) system and flow simulations were conducted on the High Performance Computing (HPC) facilities of EMPA and ETHZ using time resolved Large Eddy Simulation (LES). The wind tunnel experiment simulated a large range of turbulent flow conditions for a unit aspect ratio street canyon geometry, by using a purpose-build wind tunnel setup. A split-floor setup and turbulence generating spires and barriers were used to vary the degree of turbulence. Time resolved stereo-PIV data was used for a detailed investigation of selected cavity flows. Spatio-temporal visualizations of vortex cores using the Q criterion were superimposed on sweep and ejections events. This provided useful insights on the dynamics of shear layers and the interaction with external turbulence. It was found that moderately turbulent cases feature shear layers that produce vortices through Kelvin-Helmholtz instabilities and cases with high turbulence showed vortex shedding at the upstream edge, caused by sweep events. The time dependent analysis of the highly turbulent case showed intermittent, large scale sweep events that penetrate into the cavity. Flow simulations with LES were conducted to investigate the turbulent flow of a unit aspect ratio street canyon. For the inlet boundary con-
影响因子：
5
作者：
Letzel, Marcus Oliver;Krane, Martina;Raasch, Siegfried
通讯作者：
Raasch, Siegfried