Study on the flow mixing of hot and cold fluids in the T-junction under rolling motion condition

The present study numerically investigates the flow mixing characteristics in the T-junction with momentum ratio (M_R) of 0.95 under rolling motion condition. The effects of different inflow rates of 0.47–1.9 kg·s⁻¹ and the synergistic effects between velocity and temperature are discussed. The results show that the rolling motion significantly changes the upstream instantaneous velocity field, especially that near the wall, which induces the variations of the instantaneous M_R and the mixing length of the temperature field. The rolling motion increases the range of the velocity fluctuation while decreasing that of the temperature fluctuation. Under rolling motion condition, increasing the inflow rates decreases the range of the velocity fluctuations and inhibits the variation of M_R. This weakens the flow mixing of main and branch fluids thereby increasing the range of the temperature fluctuations. In addition, it is found that the synergistic effects between velocity and temperature occur at the junction of the main and branch fluids, where the power spectrum densities (PSDs) of y velocity component fluctuation and temperature fluctuation exhibit the same frequency peaks of 0.2 Hz, 5.8 Hz, 14.7 Hz, and 31.2 Hz. By comparing the PSDs along with the y-axis, it is revealed that the high temperature fluctuation area of y/D = 0–0.33 has a faster energy cascade with a larger slope of −5/3 in the low-frequency area (0.1–10 Hz) and −13/2 slope in the high-frequency area (>10 Hz).