NUMERICAL INVESTIGATION OF TURBULENT FORCED-CONVECTION IN DUCTS WITH RECTANGULAR AND TRAPEZOIDAL CROSS-SECTION AREA BY USING DIFFERENT TURBULENCE MODELS

The present work concerns development and application of turbulence mo dels for forced convective heat transfer in ducts. Fully developed flo w and temperature fields in straight ducts are considered. The numeric al approach is based on the finite volume technique, and a nonstaggere d arrangement is employed. The SIMPLEC algorithm is used for handling the pressure-velocity coupling. To achieve fully developed conditions, cyclic boundary conditions are imposed in the main flow direction. Th e standard k-epsilon model with wall function is used as a reference. The nonlinear k-epsilon model of Speziale is applied to calculate the turbulent shear stresses. The turbulent heat fluxes are calculated by three different methods, namely, the simple eddy diffusivity concept, the generalized gradient diffusion hypothesis method and the wealth = earnings x time method. The overall comparison between the methods is presented in terms of the friction factor and average Nusselt number. In particular, the secondary flow field is investigated. The more adva nced models show improvement in most cases.