LARGE EDDY SIMULATION OF TURBULENT FLOW IN A SQUARE DUCT - NUMERICAL INVESTIGATION INTO THE FLOW OF DENSITY AND VISCOSITY CHANGES

Large Eddy Simulation (LES) with a Finite Difference Method is presented for a fully developed turbulent flow in a square duct. Furthermore the present method is applied to investigation into a microbubble injected flow. The 3rd order up-wind finite difference is employed to dissipate numerical errors which arise from the convection term. Other partial differential operations in space are approximated with the 4th order central finite differences. A regular grid system is adopted and all velocity components and pressure are defined at the same grid points. Turbulence-driven secondary motion is reasonably simulated without a special anisotropic model. The microbubble and water mixture is treated as a homogeneous fluid with spatially varying properties. The local density and molecular viscosity of the mixture are represented as a function of the rate of bubble concentration in boundary layer. The turbulent structure depending upon the bubble injection in the boundary layer is studied.