Effect of selective modification of turbulence on two-equation models for particle-laden turbulent flows

The effect of selective modification of turbulence by particles on κ-ε models for dilute two-phase flows has been evaluated using data from direct numerical simulation of particle-laden isotropic turbulence. Simulation results were obtained using as many as 64³ grid points and up to 10⁶ particles. The ratio of the particle time constant to large-eddy turbulence time scale varied from 0.14 to 1.50 and particle mass loadings of 0.0, 0.1, 0.5, and 1.0 were used in the simulations. Simulation results demonstrate that the balance between enstrophy production by turbulent vortex stretching and viscous destruction is disrupted by momentum exchange with the particle cloud. Selective modification of the turbulence by lighter particles results in a significant attenuation of enstrophy production by turbulent vortex stretching. The decrease in enstrophy production causes the model constant C_ε2 to increase for large mass loading. Heavy particles are found to act as a sink of enstrophy for all mass loadings used in the simulations. Preferential concentration of lighter particles by turbulence, however, can generate vorticity fluctuations, especially at higher mass loadings. For these cases conventional modeling of the destruction of dissipation by particles term in the ε equation requires that C_ε3 be negative.