On RANS-based models for prediction of turbulent flow and heat transfer in ribbed ducts

Abstract

Rib roughness introduced in flow passages is a popular method of enhancing heat transfer in the cooling/heating passages, e.g., in turbine blades, combustors, and compact heat exchangers. It is essential to accurately predict the enhancement of heat transfer generated by the ribs to ensure good design decisions. The enhancement might be predicted by experiments and/or numerical methods. This study is focused on numerical methods, based on computational fluid dynamics (CFD). One of the main difficulties in CFD is the reliable modelling of the underlying physics of the turbulence. One way to handle this problem could be numerically solve the Reynolds-averaged Navier-Stokes equations (RANS), the energy equation and proper models for the turbulence field. This chapter describes some recent advances and efforts to validate and apply RANS-based models for prediction of turbulent flow and heat transfer in ribbed ducts, relevant to gas-turbine cooling and heat exchange in some compact heat exchangers. The evaluated turbulence models include a basic low-Reynolds-number (low-Re) k −� model (AKN), and two promising higher-order models: namely, the explicit algebraic stress model (EASM), and the k − � − v 2 models. All these models are validated with available 2D and 3D experimental heat transfer and fluid-flow data. Some conclusions are reached on their suitable application. In addition, computation is also conducted to clarify the contradiction existing on which pointing direction is preferable for V-shaped ribs. The results of different rib angles (45 o and 90 o ) and Reynolds number (14,000-30,000) are compared to determine the suitability of different rib orientations. Detailed velocity and thermal field results have been used to explain the effects of the inclined ribs and the