Concentration-Based Decomposition of the Flow around a Confined Cylinder in a UV Disinfection Reactor

Abstract

The proper orthogonal decomposition (POD) is applied to spatial concentration data, obtained using laser-induced fluorescence (LIF), for the flow around a confined circular cylinder (R=4,900) and compared with their corresponding velocity and vorticity fields. The velocity, vorticity, and concentration modes identify the dominating coherent structures, i.e., shear layer rollup, instantaneous recirculation and von Karman vortex shedding. In the velocity and vorticity decomposition, instantaneous recirculation, and von Karman vortex shedding are represented in the highest energy modes. However, in the concentration decomposition, the most energetic modes represent the regions with strong concentration intermittency, i.e., where no dye is present, whereas the coherent structures, which are identified in the highest modes in the velocity and vorticity decomposition, are only found in the less energetic modes. The concentration-based decomposition identifies the shear layer around the cylinder, which is only partially captured by its vorticity-based counterpart.