Large-eddy simulations of structure effects of an upstream elbow main pipe on hot and cold fluids mixing in a vertical tee junction

Thermal striping is a possible cause of thermal fatigue in the piping systems used in e.g. nuclear power plants. In the present work, the mixing of a hot and a cold fluid stream in a vertical tee junction with an upstream elbow main pipe is numerically predicted with large-eddy simulation. Two parameters were varied in this study: the ratio of the curvature of the elbow pipe over the diameter of the main pipe, and the dimensionless horizontal distance between the elbow pipe and the branch. The normalized mean and RMS temperature and velocity were numerically examined to investigate how the two above parameters influence the mixing. The numerical results show that the larger elbow curvature ratio and dimensionless distance would weaken the temperature and velocity fluctuations because of a reduction of the secondary flow in the elbow.