LAUSR

Abstract This paper presents wall-resolved Large-Eddy Simulations (LES) of thermal mixing mechanisms both in horizontal and vertical T-junctions. The mass flow rate ratio ( m m / m b ) of the mixing fluids is 3 and the temperature difference ( T m - T b ) is 180 K. The numerical results are validated with experimental data from the horizontal T-junction (warm horizontal main pipe flow and a cold branch pipe flow coming from the side) from Zhou et al. [32] and with yet unpublished measurement data of the vertical T-junction (warm horizontal main pipe flow and a cold branch pipe flow coming from above) of the Fluid-Structure Interaction (FSI) facility. In particular, we study the influence of the inflowing cold water stream in various T-junction configurations on the mixing mechanism. Additionally, this paper also contains a close investigation of temperature fluctuations in the mixing zone and a spectral analysis of the fluid temperature signal at chosen positions close to the piping material. On the whole, the predicted LES results are generally in good agreement with the corresponding experimental data for both configurations. Conforming to our simulations, a stable stratification in the horizontal configuration may be transformed into an unstable stratified flow behavior in the vertical configuration, that enhances the thermal mixing and heat transfer.