Effects of momentum ratio on thermal mixing in a horizontal T-junction under rolling motion conditions

This study investigates the thermal mixing characteristics in a horizontal T-junction with a high temperature difference of 275 K and a high pressure of 10 MPa. Three typical flow regimes of wall jet, deflecting jet, and impinging jet are established to examine the effects of momentum ratio on fluid temperature fields, velocity fields, and wall temperature fluctuations under both steady and rolling motion conditions. Numerical simulations are performed using Large Eddy Simulation (LES) and validated against experimental data obtained from Two-Color Planar Laser-Induced Fluorescence (TC-PLIF) and Particle Image Velocimetry (PIV). The results show that, under steady conditions, as the momentum ratio ( M R ) decreases from 2.73 of wall jet to 0.17 of impinging jet, the temperature uniformity gradually increases, and the mixing coefficient ( UI ) increases from 0.72 to 0.94. Rolling motion induces periodic spatiotemporal evolution of the temperature field due to additional inertial forces, further improving temperature uniformity. The mixing coefficients for wall jet, deflecting jet, and impinging jet conditions under rolling conditions stabilized downstream at 0.80, 0.85, and 0.99, respectively, representing increases of 11.1%, 16.0%, and 5.9% relative to the steady conditions. Temperature and velocity fluctuations are predominantly concentrated in the shear layers and recirculation zones, with their peak positions shifting downward as the momentum ratio decreases. The most intense wall temperature fluctuations occur at the intersecting line of the main and branch pipes, with a maximum value at x/D = −0.17, and decrease with decreasing momentum ratio. In addition, the rolling motion increases the temperature and velocity fluctuations in the T-junction, and the effect of rolling motion decreases with a decrease in the momentum ratio. This work reveals the coupled effects of momentum ratio and rolling motion on the thermal mixing mechanism in the T-junction, providing a theoretical basis for assessing thermal fatigue risks in marine pipeline systems.