Numerical Analysis of Turbulent Heat Transfer in a Square Duct with Different Rib Shapes

Abstract

Numerical analysis has been performed for three-dimensional developed turbulent flow in a square duct with rib-roughened walls. Special attention pays for the prediction of turbulent heat transfer with roughened wall. Roughened wall is composed of small ribs which are located periodically on bottom wall of square duct. In order to clarify the influence of rib cross sectional shape on flow and temperature fields, three kinds of ribs, that are square, triangular and elliptical cross section, is examined from the point of heat transfer. In numerical calculation, algebraic Reynolds stress model is selected for flow field in order to predict anisotropic turbulent flow precisely and zero equation model assuming constant Prandtl number is applied for temperature field to make clear whether such simple model is able to evaluate Nusselt number correctly. Periodic boundary condition has been used for this flow to save computational time. Calculated results of temperature field are compared with the experimental data in order to examine the validity of the presented numerical method. As a result of this calculation, it has been found out that the present method could predict temperature contour lines and Nusselt number qualitatively although agreement is certainly not perfect in all detail. Adding to this, turbulent structure is affected by rib cross section shape, although rib height is small compared with side length of square. Especially, elliptical cross section promotes the production of vertical fluctuating velocity and shear stress which leads to generate the secondary flow of the second kind more actively than the other rib shapes. At the same time, calculated results suggest that heat transfer is enhanced by the elliptical cross section.