A Particle Image Velocimetry (PIV) image processing technique has been developed which can be applied to solid-liquid two-phase turbulent flows. The main principle of the technique is to utilize a two-dimensional median filter to generate separate images of the two phases, thus eliminating the errors induced by the distinct motion of the dispersed component. The accuracy and validity of the technique have been studied in the present research for different filter widths, f, and for 4 groups of different sized dispersed particles ranging from an effective image diameter of dp=2.9 pixels to 13 pixels in combination with tracer particles with an effective image size of dt∼2.4 pixels. The results have shown that the errors introduced by the filter are negligible, and mainly arise in regions of large velocity gradients that are sensitive to the slight loss of information incurred by the processing. The filter width f also affects the algorithm’s ability to correctly separate and identify the dispersed phase particles from the two-phase images, with the main result that above a critical particle image size ratio, dp/dt≈3.0, the particle size had no significant influence on the number of particles identified, or the accuracy of the displacement calculation. Sample results of particle-fluid interaction and cross-correlation terms which can be obtained from the method are also presented. [S0098-2202(00)01104-4]

Issue Section:
Technical Papers
Keywords:
two-phase flow, velocity measurement, image processing, turbulence, flow measurement, median filters
Topics:
Displacement, Filters, Particulate matter, Errors, Fluids, Turbulence, Two-phase flow
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