Experiments on particle dispersion in a plane wake

Abstract

Detailed experimental results are presented concerning the effects of vortex structures on the solid particle dispersion process in a plane wake. Previous numerical results have indicated that vortex structures in plane wakes can disperse intermediate Stokes number particles into highly organized patterns. The cross stream spatial dispersion values associated with these particles were computed to be several times greater than that associated with fluid elements. The major objective of this study was to obtain direct experimental results concerning the time dependent particle dispersion process in a plane wake. The experimental approach used in this work primarily involves laser sheet pulsed imaging of glass bead particles in a wake downstream of a blunt trailing edge. Two sizes of glass beads with nominal diameters of 10 and 30 μm were used as particles in an air flow. The associated Stokes numbers of the particles were 0.15 and 1.4. Digital image analysis techniques were employed to identify and determine particle locations and velocities. The results demonstrate that particle dispersion in plane wakes can produce highly organized patterns of particle concentrations. The particles at intermediate Stokes number are focused into sheet-like regions near the boundaries of the large scale vortex structures. In addition the spatial dispersion of the intermediate Stokes number particles was much larger than the smaller Stokes number particles. These experimental results strongly support previous numerical simulation findings.