NASA/TM{1999{209843 Predicting Turbulent Convective Heat Transfer in Three-Dimensional Duct Flows

The performance of an explicit algebraic stress model is assessed in predicting the turbulent ow and forced heat transfer in straight ducts, with square, rectangular, trapezoidal and triangular cross sections, under fully developed conditions over a range of Reynolds numbers. Iso-thermal conditions are imposed on the duct walls, and the turbulent heat uxes are modeled by gradient-di usion type models. At high Reynolds numbers (> 105), wall functions are used for the velocity and temperature elds, while at low Reynolds numbers, damping functions are introduced into the models. Hydraulic parameters such as friction factor and Nusselt number are well predicted, even when damping functions are used, and the present formulation imposes minimal demand on the number of grid points without any convergence or stability problems. Comparison between the models is presented in terms of the hydraulic parameters, friction factor and Nusselt number, as well as in terms of the secondary ow patterns occurring within the ducts.