Large-eddy simulation of thermal stratification in a straight branch of a tee junction with or without leakage

Thermal stratification can result in thermal fatigue in the piping system of a nuclear power plant. This work focuses on a fundamental description of the thermal stratification caused by turbulent penetration and buoyancy effects using large-eddy simulations (LES) in a tee junction with a straight branch pipe. In the absence of leakage, the LES results are good agreement with the available experimental data, which validates LES as a method for predicting the thermal stratification in this system. Subsequently, the flow and heat transfer was numerically predicted using LES when leakage occurred in the straight branch pipe. The numerical results show that the thermal stratification was quickly dissipated with increasing leakage ratio. Although higher leakage ratios have a larger power spectrum density (PSD) of the temperature than smaller leakage ratios, the thermal stratification period is shorter for larger leakage ratios. It can be concluded that thermal stratification will last a long time in a straight pipe when the leakage is sufficiently small to maintain the thermal equilibrium between heat added from the main pipe and heat released to the environment, and the momentum balance between turbulence and buoyancy.

► Thermal stratification can cause thermal fatigue in a straight branch.
► It is caused by turbulent penetration and buoyancy effects.
► LES results were be in good agreement with the experimental data.
► Thermal stratification will last a long time as leakage sufficiently small.