Experimental study of particle-turbulence interaction in homogeneous turbulence

We study the clustering and settling of inertial particles in a novel experimental facility designed to produce a large region of homogeneous turbulence. Using two-dimensional particle-imaging velocimetry (PIV) and particle-tracking velocimetry (PTV), we explore particle-turbulence coupling through the full range of scales from Kolmogorov up to the integral length scale. We find particle clusters using Voronoï tesselation. These clusters are self similar, as indicated by their fractal nature and the power-law decay of their area distribution. The size of these clusters extends to the limits of our field of view, 30 cm in length, indicating the multiscale physics involved in preferential concentration. We also find that particles with Stokes number near one have the highest increase in settling velocity, up to almost three times the still-fluid value. We find further evidence that this is due to preferential sweeping, and that the effect is stronger for clustered particles. Finally, we present some evidence of inertial particles increasing the turbulent kinetic energy of the fluid phase, even for relatively modest volume fractions.