Experiments on particle dispersion in a plane wake

Detailed experimental results are presented concerning the effects of vorte x structures on the solid particle dispersion process in a plane wake. Prev ious numerical results have indicated that vortex structures in plane wakes can disperse intermediate Stokes number particles into highly organized pa tterns. The cross stream spatial dispersion values associated with these pa rticles were computed to be several times greater than that associated with fluid elements. The major objective of this study was to obtain direct exp erimental results concerning the time dependent particle dispersion process in a plane wake. The experimental approach used in this work primarily inv olves laser sheet pulsed imaging of glass bead particles in a wake downstre am of a blunt trailing edge. Two sizes of glass beads with nominal diameter s of 10 and 30 mu m were used as particles in an air flow. The associated S tokes numbers of the particles were 0.15 and 1.4. Digital image analysis te chniques were employed to identify and determine particle locations and vel ocities. The results demonstrate that particle dispersion in plane wakes ca n produce highly organized patterns of particle concentrations. The particl es at intermediate Stokes number are focused into sheet-like regions near t he boundaries of the large scale vortex structures. In addition the spatial dispersion of the intermediate Stokes number particles was much larger tha n the smaller Stokes number particles. These experimental results strongly support previous numerical simulation findings. (C) 2000 Elsevier Science L td. All rights reserved.