Experimental investigation on thermal mixing characteristics in a T-junction under rolling motion condition using TC-PLIF

T-junction is widely used in the marine engineering equipment, which will be in a rolling motion state during operation. The additional inertia force generated by rolling motion can cause unstable fluid flow and a strong thermal mixing inside the T-junction, increasing the thermal fatigue damage of the pipeline. An experimental study was conducted to investigate the thermal mixing characteristics in the T-junction under static and rolling motion conditions by Two-Color Planar Laser-Induced Fluorescence (TC-PLIF) technique. The main fluid Reynolds number (Re_m), inflow rate ratio (R), and rolling Reynolds number (Re_r) range from Re_m = 2110 to 15,850, R = 1 to 20, and Re_r = 0 to 3520, respectively. The results show that the rolling motion causes the branch jet to sweep up and down in the T-junction, and the vortex structure is periodically generated in the temperature shear layer, which promotes the thermal mixing of cold and hot fluids and increases the fluid temperature fluctuation. At the same time, the jet sweeping phenomenon caused by the rolling motion makes the leading edge and trailing edge shear layers bifurcate and recombine into two pairs of temperature shear layers, which expands the range of thermal mixing and makes the average temperature distribution more uniform than that under static condition. The influence of rolling motion on the temperature field could be decreased with the decrease of Re_r and/or R, as well as the increase of Re_m. Additionally, the mathematical equations of the mean jet trajectory suitable for the thermal mixing of cold and hot fluids in a T-junction under static and rolling motion conditions are established. The research results are expected to provide theoretical basis and technical support for pipeline design under rolling motion conditions.