Fully Coupled Large Eddy Simulation of Conjugate Heat Transfer in a Ribbed Channel with a 0.1 Blockage Ratio

Joon Ahn,Jeong Chul Song,Joon Sik Lee

doi:10.3390/en14082096

Abstract

Large eddy simulations are performed to analyze the conjugate heat transfer of turbulent flow in a ribbed channel with a heat-conducting solid wall. An immersed boundary method (IBM) is used to determine the effect of heat transfer in the solid region on that in the fluid region in a unitary computational domain. To satisfy the continuity of the heat flux at the solid–fluid interface, effective conductivity is introduced. By applying the IBM, it is possible to fully couple the convection on the fluid side and the conduction inside the solid and use a dynamic subgrid scale model in a Cartesian grid. The blockage ratio (e/H) is set at 0.1, which is typical for gas turbine blades. Through conjugate heat transfer analysis, it is confirmed that the heat transfer peak in front of the rib occurs because of the impinging of the reattached flow and not the influence of the thermal boundary condition. When the rib turbulator acts as a fin, its efficiency and effectiveness are predicted to be 98.9% and 8.32, respectively. When considering conjugate heat transfer, the total heat transfer rate is reduced by 3% compared with that of the isothermal wall. The typical Biot number at the internal cooling passage of a gas turbine is <0.1, and the use of the rib height as the characteristic length better represents the heat transfer of the rib.

Highlights

One way to ensure that a gas turbine engine is highly efficient is to increase the turbine inlet temperature
In this study, immersed boundary method (IBM)-based LES was performed for conjugate heat transfer inside a ribbed channel
The main results obtained through the simulation can be summarized as follows: (1) The heat transfer peak that occurs in front of the rib is not caused by unheated ribs but rather by impinging cold fluid

Summary

Introduction

One way to ensure that a gas turbine engine is highly efficient is to increase the turbine inlet temperature. Fedrizi et al [14] investigated the problem of thermal boundary conditions by performing conjugate heat transfer experiments on triangular channels with angled ribs. LES predicted the experimental results well on the channel wall; the local heat transfer distribution at the front and rear sides of the rib indicated some variation [17,18]. In this study, LES that included conjugate heat transfer was performed on a gas turbine rib generator with a typical blockage ratio of 0.1. We examined whether the rib height or blade thickness was appropriate as the characteristic length of Bi. In addition, we introduced the immersed boundary method (IBM) to perform a fully coupled conjugate heat transfer analysis. We present the thermal performance of the rib as a fin in the ribbed channel and discuss the appropriate characteristic length defining the Biot number

Numerical Methods

Time-Averaged Flow Fields and Heat Transfer Coefficient

Turbulence Statistics and Instantaneous Thermal Fields

Conclusions