Modeling And Simulation Of Extra-Dissipation In Homogeneous Isotropic Turbulence

There are two main problems in the gas-particles two-phase turbulence flows:particles dispersion and turbulence modulation. It is more difficult to describe the principle of turbulence modulation in gas-particle two-phase flow. When particles appear in the carrier flow,the k-εtwo equations for flow turbulence will produce extra terms, i.e. extra dissipation of kinetic energy and its dissipation rate, and the turbulent kinetic energy will be enhanced or attenuated. Turbulence modulation is one of the crucial problems in two-phase flow,the effect of the particles on the turbulence of the carrier phase is important,the key point is to develop a reasonable extra terms model in gas-particle two-phase flow. Modeling these extra terms can come down to the fluid-particle correlated dissipation rate closure. In this thesis,based on dimensional analysis, we use mass-weighed averaged unified second-order moment (MUSM) method and probability density distribution function (PDF) method separately, to construct the explicit algebraic expressions of fluid-particle correlated dissipation rate and fluid-particle correlated turbulence kinetic energy. In order to consider the influence of particle inertia and fluid-particle relative drift velocity, the inertia effect,the crossing-trajectory effect and the continuity effect are introduced in the turbulent modulation to modify time scale. To test the new models, the DNS result of forced isotropic turbulence (Bovin et al. 1998) and decay isotropic turbulence (Elghobashi 2003) were simulated using them. Both the fluid-particle correlated kinetic and its dissipation rate were simulated and compared with DNS data. It shows that these new model can reflect the time scale change of gas-particle interaction in turbulence modulation.