Turbulence modification in particle-laden confined jets -numerical simulation by multiple-scale k-ε model

The interaction between dispersed particles and fluid turbulence for circular confined jets was investigated numerically by a multiple-time-scale particle-laden turbulence model. Two kinds of size classified spherical particles, which were smaller than or greater than the Kolmogorov lengthscale of the flow, were dispersed in the inner tube upstream of the test section. The present modeling divides the energy-containing part of the spectrum into two regions and considers the energy transfer from large turbulent motion to small scales by particles. Numerical simulations were performed by the two-way coupling simulations between the Eulerian k-ε model and the particle Lagrangian simulation. Turbulence attenuation in air was observed in the presence of particles smaller than the Kolmogorov lengthscale of the flow, which can be also predicted by the present multiple-time-scale model. The transfer rate of turbulence energy was reduced by the particle drag, therefore the turbulence energy was attenuated. Particles which were several times the Kolmogorov lengthscale augmented turbulence intensity of water. The particle concentration fluctuations increased the turbulence energy in production range, which induced enhancing the energy transfer rate from production range to transfer range and yielded an increase in the dissipation rate of turbulence kinetic energy. These results are consistent with prior studies in channel flow and wall jet by Sato (1996). The present study ensures the ability of the multiple-time-scale model in which several time scales are required to characterize turbulence modification by particles.