Direct Measurement of Turbulence Structures in a Standard Jar Test Tank Using PIV System

by Chen-Yu Cheng, (S.M.ASCE),
Joseph F. Atkinson, (A.M.ASCE),
Marcus I. Bursik,

Document Type: Proceeding Paper

Abstract: Particle image velocimetry (PIV) is applied to the measurement of instantaneous two-dimensional velocity fields in a standard 2-liter jar test tank for several different impeller speeds. General flow patterns were obtained for the whole tank, which showed an apparent secondary flow, as well as more detailed measurements taken at different locations within the jar. Each of these latter measurements involved detailed analyses of viewing areas slightly greater than 1 cm² and these data were used to estimate the spatial variation of turbulence integral length scale and dissipation rate. These, in turn, are used to calculate local values for the velocity gradient, G. The data were analyzed using spatial filters to reveal the turbulence structures, both in terms of fluctuating velocity and vorticity fields. The results demonstrate strong spatial variations of the flow characteristics in the jar. In some areas, for instance near the impeller, strong vortex motion is seen, while at other locations a laminar flow-like pattern is observed. The result show contradiction to current practice which assume that the flow in the tank is homogeneous.

Subject Headings: Flow measurement | Turbulence | Particle velocity | Flow patterns | Data analysis | Spatial data | Imaging techniques

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