Analysis of thermal mixing characteristics in different T-junction configurations

Abstract

High frequency temperature fluctuations in the near wall region of turbulent thermal mixing processes of hot and cold fluid streams in T-junctions cause unexpected fatigue cracking of piping systems. For the prediction of these frequencies of temperature fluctuations in the flow, the Large-Eddy Simulation (LES) method is most approciate. In this paper, we present a detailed study of thermal mixing processes in different T-junction configurations. Numerical results of the horizontal T-junction configuration are validated with experimental data obtained from the Fluid-Structure-Interaction (FSI) test facility at the University of Stuttgart. In the main and branch pipe water streams flow with a temperature difference of 65 K. Furthermore, in all investigated cases a constant mass flow rate ratio (main/branch) of 4:1 is maintained, respectively. Herein we discuss in detail the impact of the entrance orientation of the cold branch pipe, the thermal stratification, the turbulent thermal mixing and the temperature fluctuations along the downstream. Our study consider additionally the second-order statistics of the flow and spectral analysis of fluid temperature fluctuations from the near-wall region. The flow simulations are coupled with the heat conduction in the solid material in order to take account of the thermal fluid-structure interaction.