Numerical simulation for heat and fluid characteristics of square duct with discrete rib turbulators

Abstract

Attachment of rib turbulators to flow passages is one of the popular means of heat transfer enhancement. Typical use of the rib turbulators is found for example in the serpentine cooling air channel for the internal cooling of the gas turbine blades. Many studies therefore have been carried out for the heat transfer in ribbed channels and various types of ribs have been tested. A standard case of full-span ribs attached perpendicularly to the flow direction has been the first target and its friction and heat transfer characteristics have been reported in the references [1–3]. Further studies were made for other cases of attaching oblique ribs and V-shaped ribs to the channel wall. In these cases, secondary flow is incurred in the channel and enhances the fluid mixing between the near wall and core regions in the duct, eventually resulting in the enhancement of local heat transfer at the channel walls [4–6]. Discrete ribs also drew attention with which heat transfer enhancement due to the incurred secondary flow is achieved paying smaller pressure loss penalty [7– 10]. In relation with the existence of the spanwise gaps, secondary flows are generated downstream their spanwise edges. Generation of the secondary flows in addition to the flow separation and reattachment makes the phenomenon quite complicated with the discrete ribs. Detailed studies of the flow structure and characteristics of the related heat transfer are required but such studies have scarcely been made so far. In the present article, some results of the three-dimensional numerical computation conducted for flow and thermal fields over two types of array of ribs attached to a channel wall will be presented. One is of fullspan ribs and the other is of discrete ribs, where both arrays are attached in a position perpendicular to the flow direction. The discussion will be given to the effects of three-dimensionality and unsteadiness of the flow and thermal fields for twofold purposes, one to test the applicability of numerical study to the type of flow under concern and another to provide hints to experimental works to be made in future.