Direct numerical simulation of particle clustering and turbulence modulation: an Eulerian approach

Abstract

We present a new Eulerian framework for the computation of turbulent compressible multiphase channel flows, specifically to assess turbulence modulation by dispersed particulate matter in dilute concentrations but with significant mass loadings. By combining a modified low-dissipation numerical scheme for the carrier gas phase and a quadrature-based moment method for the solid particle phase, turbulent statistics of the fluid phase and fluctuations of the particle phase may be obtained as both are resolved as coupled fields. Using direct numerical simulations, we demonstrate how this method effectively resolves the turbulent statistics, kinetic energy, skin friction drag, particle mass flow rate and interphase drag for moderate-Reynolds-number channel flows for the first time. Validation of our approach to the turbulent particle-free flow and the turbulent particle-laden flow proves the applicability of the carrier flow low-dissipation scheme to simulate relatively low-Mach-number compressible flows and of the quadrature-based moment method to simulate the particle phase as an Eulerian field. This study also rationalises the computed interphase drag modulation and total Reynolds shear stress results using a simplified analytical approach, revealing how the particle migration towards the wall can affect the drag between the two phases at different Stokes numbers and particle loadings. Furthermore, we show the effect of near-wall particle accumulation on the particle mass flow rate. Using our Eulerian approach, we also explore the complex interplay between the particles and turbulent fluctuations by capturing the preferential clustering of particles in turbulence streaks. This interplay leads to turbulence modulations similar to recent observations reported in prior computational works using Lagrangian simulations.