MS Defense: Shiyan Chen
Laboratory and Field Investigation of Buoyant Plume Structure and Ground Level Concentration
Department of Mechanical Engineering
Advisor: Professor Marko Princevac
Abstract: Atmospheric surface layer (ASL) is a part of the atmosphere that is strongly affected by Earth's surface. Biosphere is located within ASL, which is where most human activities take place, where animals and vegetation live. In recent years, increasing concern over urban centered air pollution lead to studies on the prediction and assessment of the dispersion of toxic material in the urban environment. Many of them are of a fluid mechanical nature. In the urban ASL, the pollutant dispersion behavior is still not fully resolved since 1) anthropogenic sources of pollutants which are difficult to model are concentrated in urban areas; and 2) the conventional ASL scaling theories are challenged by significantly increased urban roughness and horizontal inhomogeneity. Therefore, air quality studies are especially acute in areas of increasing urbanization. This thesis is motivated by this need, and both field measurement and laboratory simulation are conducted to address this issue.
First, qualitative dye visualizations were performed in the laboratory. The experiments were conducted in a neutrally stratified boundary layer and the aim of the study was to evaluate the influence of ambient flow velocity, obstacle array sizes, plume buoyancy and exhaust stack velocity on the plume dispersion.
Next, the tracer study was conducted in July 2008 in which a tracer gas was released from a distributed generation (DG) station in Palm Springs, California. Total of seven, three day-time and four night-time dispersion experiments were conducted.
Thirdly, a laboratory Particle Image Velocimetry (PIV) and Planar laser Induced Fluorescence (PLIF) combo technique is utilized to investigate the urban pollutant dispersion from an elevated buoyant source in a scaled down model. The laboratory parameters were designed using five scaling laws and the plume rise and plume structure, the plume dispersion, along with the ground level concentration (GLC) of the plume have been observed and determined from scaled data. Plume structure and plume rise were successfully measured using standard PLIF technique. Several alternative methods were used to investigate ground level concentrations. The laboratory results are compared with the field data and Gaussian plume dispersion model.