Numerical Analysis of Turbulent Flow in a Square Duct with Periodic Rib-Roughened Wall

Abstract

Numerical analysis has been performed for three-dimensional developing turbulent flow in a square duct with rib-roughened walls by using an algebraic Reynolds stress model. This squared sectioned duct with roughened wall has been applied for coolant passage employed in gas turbine blades and heat exchanger in many engineering fields. Roughened wall is composed of many ribs, which is periodically located along the flow on the bottom wall of a square duct. In the numerical calculation, periodic boundary condition has been used for this flow and an algebraic Reynolds stress model is adopted in order to predict preciously Reynolds stresses. Calculated results of mean velocity and Reynolds stresses are compared with the experimental data in order to examine the validity of the presented numerical method and an algebraic Reynolds stress model. It has been pointed out as a characteristic features from the experimental result that secondary flow of the second kind is generated near roughened wall with flowing to roughened wall. The present method could predict its phenomenon correctly and reproduce well mean velocity profile distorted by the secondary flow. Besides, calculated results of Reynolds stresses are in good agreement with the experimental results, especially, shear stress distributions, which are characterized by generating the opposite sign regions, are predicted well as a result of estimating the secondary flow pattern preciously. Since the presented turbulent model is defined as high Reynolds number model, wall function is used for setting boundary conditions of turbulent energy and dissipation. As for this wall function, calculated results suggest that the universal constant of log-law velocity which is assumed in wall function, has to be changed according to the wall condition, that is smooth or rough.