The change in inertial particle clustering in turbulent flow due to collision-coagulation: A Voronoi analysis

Two-dimensional Voronoi analysis is used to quantify the preferential concentration (clustering) of inertial particles in homogeneous isotropic turbulence. The diameter of particles is one order of magnitude smaller than the Kolmogorov length scale of turbulent flow, and the density of particle is more than one order of magnitude larger than that of the fluid. We study the influence of particle collision-coagulation on particle clustering and how it relates to particle and turbulent parameters (particle Stokes number St, particle diameter d, and turbulent Reynolds number Reλ). The probability density function (PDF) of Voronoi area (of particles) normalized by its average shows different properties due to particle collision-coagulation. The influence of particle collision-coagulation on particle clustering is mainly in the small scale (area) range, with the changes in PDF limited in the large area regime. In the small area regime, the PDF decreases as a result of particle collision-coagulation when compared to the control case with non-colliding particles. This decrease is noticeable in the range of A/A¯≲2×10−2. The decrease in the PDF becomes more significant with increasing particles Stokes number until a turning point at St∼0.5, after which the effect diminishes gradually. The influence of particle collision-coagulation on particle preferential concentration is also related to the particle diameter d. As d increases, the PDF value decreases obviously at small areas. When the particle diameter is made three times larger, the range where PDF decreases extends to A/A¯≲10−1. We also study the influence of turbulent Reynolds number. For Reynolds number in the range of Reλ=84–189, we find that the decrease in the PDF due to particle collision-coagulation is independent of Reλ for particle with St = 0.1 and St = 1.0. In the large area regime, the PDF increases slightly, indicating an increasing void region due to particle collision-coagulation.