Modal analysis of particle laden turbulent flow in a square duct

Inertial particles in a turbulent flow have been shown to profoundly affect the morphology and intensity of coherent flow structures. Proper orthogonal decomposition (POD) is used in the present work to study the influence of particles on coherent flow structures by comparing unladen and laden flow results from two-way coupled DNS simulations with Lagrangian point-particle models. We exploit information on the contribution of most energetic structures to the overall turbulent kinetic energy (TKE) provided by POD to analyze turbulent modulation by particles. The study uses data from a fully developed turbulent flow in a square duct at a bulk Reynolds number of 20,000 with particle mass fraction ratios ranging from 0 to 1. The spatial modes identified by the POD show morphological differences with increasing particle loading. Selected terms from the turbulent kinetic energy budget and spectral analyses are used to help interpret the POD results. POD of the fluctuating particle concentration and velocity fields projected onto the velocity fluctuations modes allows analyzing correlations between the most energetic particle and flow structures.