Turbulence-induced preferential concentration of solid particles in microgravity conditions

A box of near-isotropic, particle-laden turbulence was flown aboard NASA's reduced gravity aircraft in order to measure the turbulence-induced preferential concentration of solid particles in microgravity. Three particle sets of Stokes numbers based on the fluid Kolmogorov time scale of approximately 0.5, 5, and 50 were tested for relative amounts of preferential concentration. Eight fans in each corner of a Lexan box generated fluid turbulence. Particle concentrations were measured using an imaging system consisting of a camera viewing perpendicular to a white light sheet. Post-processing of video images found largest concentration gradients for the intermediate-sized particles of Stokes number 5, closely followed by the Stokes number 0.5 particles. The experimental results agreed well with the trends seen in direct numerical simulations. The quantitative effects of turbulence modulation by the presence of particles were not measured in the experiment, but were most likely present.