Thermal fatigue in a T-junction is of crucial importance issue for the coolant system of nuclear energy plants. The dynamic mode decomposition (DMD) is employed to analyze the snapshot data from simulation results with applying large eddy simulation (LES). The thermal mixing flow in a square T-junction is simulated at the impinging jet (MR = 0.2). The temperature difference of hot and cold fluids is 15 K. The corresponding Reynolds number is about 20000. The results show that the frequency of the velocity modes is not equal to that of the temperature mode. The frequency of the temperature mode 1 is more than 40% higher than that of the velocity mode 1. The main spatial structures of the temperature field and the velocity field are alternately arranged along the trajectory of the branch fluid entering the main duct. The main coherent structure of the velocity field arrives at the bottom wall of x/Dm = 1, whereas for the temperature field, it basically appears in the region of x/Dm = 0.6 – 0.8. The negative structures of the velocity mode 1 induces the positive structures of the temperature mode 1. Also, the coherent structures of Modes 1 and 2 grow along the normal direction during downstream propagation.
Keywords Dynamic mode decomposition, T-junction, Impinging jet, Frequency, Coherent Structure
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