[en] The aim of this work is to develop tools and models to study thermal large-eddy simulations of low Prandtl number fluid flows. The goal is to quantify temperature fluctuations near the walls in order to estimate the risk of thermal striping. For low Prandtl number fluid flows, thermal structures are much smaller than dynamic ones; this allows the use of a relatively coarse meshing grid associated to a wall law and a good sub-grid scale model for velocity. To start with, we validated our approach by studying periodic plane channel and analysed the impact of different thermal boundary conditions: isothermal, iso-flux and conjugate heat transfer. Moreover, the periodic channel study permitted the generation of a turbulent inlet for a mixing Tee junction. To keep a good compromise solution between accuracy and computational cost, we estimated the length of the three pipe sections of the mixing Tee. On several configurations of mixing Tees, points with maximal values of temperature fluctuations were localized, and later a spectral analysis was made. (author)