力学与湍流重点实验室学术报告（报告人：Prof. James Wallace）
发布时间: 2009-07-13 09:12:00
SEMINAR SERIES
北京大学工学院 ![]()
力学与空天技术系
湍流与复杂系统国家重点实验室
题目：Scalar dispersion in an idealized urban street canyon within a turbulent boundary layer
报告人 Prof. James Wallace
Department of Mechanical Engineering at the University of Maryland
报告内容摘要：
Measurements have been made of the scalar dispersion of smoke released from a two-dimensional slot in the wall perpendicular to a boundary layer flow and located parallel to and midway between two square obstacles placed on the wall. The Reynolds number of the boundary layer at the slot location without the obstacles in place is $R_{\theta} \approx 980$. Two optical systems with CCD cameras facing each other have been used to measure simultaneously the velocity and scalar concentration fields, respectively, with PIV and Mie scattering diffusion. The data provides detailed information about the velocity field, momentum and scalar fluxes and scalar concentration for this environmentally relevant geometry. The results of the velocity field and scalar concentration and flux measurements in the streamwise plane are reported for spacings between the obstacles of 1-8 obstacle heights. The mean flow measurements reveal the increased complexity of the canyon flow with increasing obstacle spacing. A primary vortex, with negative spanwise vorticity occurs for all obstacle spacings and is driven by the flow above. The circulation region of this vortex extends above the level of the top of the obstacles. For spacings of $2h$ and greater, a secondary vortex with positive vorticity appears in the upstream corner of the canyon, and a tertiary vortex with negative spanwise vorticity begins to appear in the downstream corner of the canyon for $6h$. The spatial distribution of the level of turbulence within and around the canyon, as indicated by the contours of two-dimensional turbulent kinetic energy $\f{1}{2}\ol{(u^2$ + $v^2$)$, and of the Reynolds shear stress are related to the spatial distribution of the scalar concentration and scalar flux distributions.
报告人简介：
Dr. James Wallace，Professor in the Department of Mechanical Engineering at the University of Maryland at College Park. He received his B.S. and M.S. degrees in 1962 and 1964 from the Georgia Institute of Technology and his D. Phil. in Engineering Science from Oxford University in 1969. He was on the research staff of the Max-Planck-Institut für Strömungsforschung (fluid flow research,) in Göttingen, Germany from 1969 until he joined the faculty of the University of Maryland in 1975. In addition to his research and teaching, he has held several academic administrative positions at Maryland. From 1985 - 87 he was the Assistant Provost of the Division of Mathematics, Physical Science and Engineering. From 1993 - 1998 he served as Associate Chairman for Graduate Studies in the Department of Mechanical Engineering. He currently is the Board Chair of the Burgers Program for Fluid Dynamics. He also helped found and directed two Science, Technology and Society programs at Maryland and has directed the Gemstone Program for undergraduate honors team research since 2001.
主持人：陈十一 教授
时 间：7月23日（周四）上午10:00
地 点：力学楼434会议室
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