The small-scale structure of the fluctuating passive scalar field in a turbulent boundary layer

PROPOSAL编号：CTS-0303406 PROPOSAL类型：调查员INITIATEDPRINCIPAL调查员：Donald R.WEBSTERINSTUTION：佐治亚理工学院。湍流边界层中脉动被动标量场的小尺度结构湍流中被动标量的混合和输运是许多自然和工程环境中发生的重要过程。常见的例子包括水体中的污染物排放、大气中的化学羽流和反应堆中的化学混合。尽管几十年来的研究旨在了解湍流传输的动力学，但标量场继续挑战准确的理论预测。由于缺乏一个通用的理论来预测湍流传输的统计性质，最终需要进行实验测试来预测和优化许多实际情况下的混合效率。这一过程效率低，成本高，因此，标量波动的普遍理论仍然是非常可取的。本文对切变湍流的研究有以下目的：(1)考察标量方差耗散率的动力学；(2)研究多点相关器作为描述小尺度湍流结构及其与传统结构函数的关系的工具的行为和用处。此外，我们还建议研究结构函数的各向同性和各向异性分量及其各自的标度行为。将对明渠湍流边界层中的化学羽流进行实验。平面激光诱导荧光(PLIF)技术将用于记录高施密特数浓度场的时间序列。这些测量解析了标量场的Batchelor长度标度。将考察三个雷诺数和三个平均标量梯度之间的变化。所提出的实验结果将影响模拟策略和我们对湍流剪切流中小尺度和大尺度行为之间的耦合的基本理解。一名研究生(博士水平)和一名本科生将接受高级实验技术和基础湍流研究方面的培训。佐治亚理工学院在代表不足的群体的研究生教育方面处于全国领先地位，将尽一切努力吸引这样的学生加入这个项目。

ABSTRACTPROPOSAL NO.: CTS-0303406PROPOSAL TYPE: INVESTIGATOR INITIATEDPRINCIPAL INVESTIGATORS: DONALD R. WEBSTERINSTITUTION: GEORGIA TECH. THE SMALL-SCALE STRUCTURE OF FLUCTUATING PASSIVE SCALAR FIELD IN A TURBULENT BOUNDARY LAYERMixing and transport of passive scalars in turbulent flows are important processes occurring in many natural and engineered environments. Common examples include contaminant discharges in water bodies, chemical plumes in the atmosphere, and chemical mixing in reactors. Despite decades of research aimed at understanding the dynamics of turbulent transport, scalar fields continue to defy accurate theoretical predictions. The lack of a general theory to predict the statistical nature of turbulent transport ultimately requires experimental tests to predict and optimize mixing efficiency for many practical situations. This procedure is inefficient and costly, thus a universal theory for turbulent fluctuations of scalar quantities continues to be highly desirable. This study of a turbulent shear flow has the following objectives: (1) examine the dynamics of the scalar variance dissipation rate, and (2) study the behavior and usefulness of multi-point correlators as a tool to represent small-scale turbulence structure and its relation to the traditional structure functions. We additionally propose to examine the isotropic and anisotropic components of structure functions and their respective scaling behavior. Experiments will be performed for a chemical plume in a turbulent boundary layer of an open channel flow. The planar laser induced fluorescence (PLIF) technique will be used to record time series of the high Schmidt number concentration fields. The measurements resolve the Batchelor length scale of the scalar field. Variation among three Reynolds numbers and three mean scalar gradient cases will be examined. The proposed experimental results will impact both modeling strategies and our fundamental understanding of the coupling between small-scale and large-scale behavior in turbulent shear flows. One graduate student (Ph.D. level) and one undergraduate student will be trained in advanced experimental techniques and fundamental turbulence research. Georgia Tech is a national leader in graduate education of underrepresented groups, and every effort will be made to attract such a student to this project..