EFFECT OF SELECTIVE MODIFICATION OF TURBULENCE ON 2-EQUATION MODELS FOR PARTICLE-LADEN TURBULENT FLOWS

The effect of selective modification of turbulence by particles on K-e psilon models for dilute two-phase flows has been evaluated using data from direct numerical simulation of particle-laden isotropic turbulen ce. Simulation results were obtained using as many as 64(3) grid point s and up to 10(6) particles. The ratio of the particle time constant t o large-eddy turbulence time scale varied from 0.14 to 1.50 and partic le mass loadings of 0.0, 0.1, 0.5, and 1.0 were used in the simulation s. Simulation results demonstrate that the balance between enstrophy p roduction by turbulent vortex stretching and viscous destruction is di srupted by momentum exchange with the particle cloud. Selective modifi cation of the turbulence by lighter particles results in a significant attenuation of enstrophy production by turbulent vortex stretching. T he decrease in enstrophy production causes the model constant C-epsilo n 2 to increase for large mass loading. Heavy particles are found to a ct as a sink of enstrophy for all mass loadings used in the simulation s. Preferential concentration of lighter particles by turbulence, howe ver, can generate vorticity fluctuations, especially al higher mass lo adings. For these cases conventional modeling of the destruction of di ssipation by particles term in the epsilon equation requires that C-ep silon 3 be negative.