Effect of vortex fluctuation in a 90-degree curved pipe on the surface fluctuation of an ejected liquid jet

Improving the thermal efficiency of internal combustion engines requires a high compression ratio, a high thermal load, and high mechanical strength in the combustion chambers. However, they will promote excessive temperatures within the combustion chamber and increase the likelihood of knocking. As the piston reciprocates, the engine oil injected into the piston crown oil gallery can oscillate within the gallery to reduce the piston temperature. However, the interaction between the ambient air and the interface of the axial jet liquid column results in unstable fluctuations, significantly affecting the filling rate of the oil gallery. In this study, the fluctuation of the jet interface is analyzed by changing the Reynolds number (Re) and bending radius R of the nozzle. Two-dimensional/two-component and two-dimensional/three-component particle image velocimetry are used to measure the flow fields in the longitudinal section of two bent nozzles with small (R = 15 mm) and large (R = 60 mm) curvature radii and horizontal cross-sections at 4D, 2.5D, and 1D from the exit of each bent nozzle, respectively, to explore the causes of the fluctuating internal flow. By calculating the secondary flow intensity Se on the inner and outer wall sides of the nozzle, the inner and outer jet interface width changes, and the different fragmentation mechanisms of the jet interface, it is shown that the higher frequency of the high-speed core region at the outer wall side of the nozzle interior can drive the waveform on the outside of the jet interface to break and produce small-diameter droplets easily.