Measurement of particle preferential concentration in homogeneous isotropic turbulence*

Preferential concentration is a phenomenon where particles in turbulent flow concentrate in regions of low vorticity and high strain rate, forming clusters. This phenomenon is prevalent in nature and various industrial environments. Previous measurement systems for detecting this phenomenon have been based mostly on discrete images. We have developed a new continuous measurement system comprised of a photomultiplier tube (PMT), custom-designed lens tube, and a continuous wave (CW) Nd:YAG laser. A unique calculation method has been devised to estimate the cluster size from the Mie scattering of the particles. Experiments were conducted in a homogeneous isotropic turbulence (HIT) chamber with no mean flow, using particles with Stokes number (St) near unity. As the Stokes number was varied, the new technique showed similar trends in cluster size compared to a conventional camera-based method.