Large-eddy simulation on thermal-mixing experiment at horizontal T-junction with varied flow temperature

Abstract

In a thermal-mixing pipe-flow close to a mixing tee, where flow streams with different temperatures are mixed, high frequency temperature fluctuations can be created and lead to material damage in the pipe line. Such damage mechanism is denoted as thermal fatigue and constitutes a potential risk to the safety of the piping system in nuclear power plants. At the University of Stuttgart, the Fluid-Structure Interaction (FSI) test facility has been constructed and operated for investigating flow-mixing mechanism causing thermal fatigue at a pipeline T-junction. In previous work, experimental investigation has been performed with high temperature difference between the inlet flow stream (>140 K). It has been found the temperature difference is one of the crucial factors on the damage potential due to thermal fatigue.In this work, numerical simulations have been performed on the previous experiments with the varied flow temperature. Wall-resolved Large-Eddy Simulation (LES) method has been applied in the simulations. Distributions of flow parameters have been reproduced for understanding of mixing behavior at high temperature difference. The simulation results provide a good illustration on the flow region and agree well with the experimental data. Moreover, the new mixing phenomenon, tangential oscillation of thermal stratification, has been identified from the analysis on the previous experimental data. Additional methods have been applied in this work for reproducing this phenomenon. The simulation results have confirmed that the tangential oscillation has been initiated in the thermal-mixing process. The characteristic frequency of this phenomenon can be found in the frequency spectra of the temperature monitor data at several different monitor positions.