Dispersion of solid particles in compressible mixing layers

Flow visualization and subsequent digital image processing were used to investigate the dispersion of solid particles in compressible free shear layers with convective Mach numbers of 0.51 and 0.86. A sheet of light formed using a Nd: YAG pulsed laser was used to illuminate the dispersed particles of nominal diameters 5, 17, and 62 mu m. An intensified CCD camera captured images of the flowfield and subsequent digital image processing was used to locate particles in the images. Visual and statistical results for the M sub(c) = 0.51 case showed dispersion trends similar to those in incompressible cases where particle dispersion depends largely on the ratio of particle time scale to fluid time scale (Stokes number). In particular, high levels of dispersion occurred for a range of Stokes numbers. However, results showed that three-dimensionality and disorganization of large scale structures in the higher compressibility case (M sub(c) = 0.86) drastically reduced their entrainment and dispersion capabilities. Selective dispersion of particles was not observed for the range of Stokes numbers studied in the M sub(c) = 0.86 case.