TWO-PHASE PIV FOR PARTICLE-LADEN FLOWS

The present study has developed a specialized Particle Image Velocimetry (PIV) image processing technique which can be applied to solid-liquid two-phase turbulent flows. The main principle of the technique is to utilize a 2-D median filter to separate images of the two phases, thus eliminating the errors induced by the distinct motion of the dispersed component. The main influence of the median filter on the accuracy of the displacement calculation is due to the filter width f. This has been studied in the present research by using 6 groups of different sized dispersed particles ranging from d_p = 45 μm to 300 μm in combination with tracer particles with an effective image size of d_t ~ 15 μm. The results have shown that the errors introduced by the filter are negligible, and mainly arise from the regions of large velocity gradients which 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. The number of correctly identified dispersed phase particles was found to increase with the particle size, and decrease with the filter width. Above a critical size d_p/d_t ~ 5.0, the particle size had no significant influence on the number of particles identified, or the accuracy of the displacement calculation. The results also indicated that the optimal filter width required to balance the separation of phases and the accuracy of calculation wasf/d_t ~ 2.5.