Suitability of wall-functions in Large Eddy Simulation for thermal fatigue in a T-junction

Large Eddy Simulations are performed in a T-junction to analyze the suitability of wall-functions in accurately predicting the thermal fluctuations acting on the pipe walls due to turbulent mixing. The WALE sub-grid-scale model used in the LES solver is validated with existing experimental data. In order to reduce the computational costs, Reynolds number scaling is performed while preserving the essential flow features. While the wall-function based simulation showed good agreement with the wall-resolved approach for the bulk velocity and temperature field, the corresponding RMS components were consistently under-estimated close to the wall boundaries. The same was true for the RMS fluctuations of the wall heat-flux. As a consequence, it is suggested that wall-functions should be used with caution, especially for the considered nuclear application.