VORTEX STRUCTURE ANALYSIS OF VORTEX RING COLLISION PROCESS BASED ON DIRECT NUMERICAL SIMULATION

Vortex ring collision involves intricate multi-level topological relationships of vortex structures and mechanisms of enstrophy transfer. A thorough investigation of this model contributes to the elucidation of the mechanisms involved in the interaction processes among vortex structures. Distinguishing itself from existing studies that typically focus on the transient evolution of small-scale secondary structures within vortex rings, this research employs direct numerical simulation utilizing an enhanced SIMPLE algorithm. It integrates the overall dynamic evolution with detailed analysis of vortex structure to investigate vortex ring collision models. Utilizing a high-resolution grid, we analyzed the secondary vortex structures spawned after vortex ring collisions at different Reynolds numbers. The study reveals that the vortex ring collision process is accompanied by complex topological changes in vortex structures, such as the deflection of high enstrophy regions and the elongation between vortex filaments. During collisions, the instability of the rings themselves leads to the formation of secondary vortex rings distributed according to azimuthal angles after local contacts. The secondary structures undergo a transition from non-existence to existence and from an approximately circular ring shape to a turbulent state with increasing Reynolds numbers in the flow field. Concerning the enstrophy profiles reflecting the overall flow field, an increase in Reynolds number generally results in a reduction of the initial moment of dissipation rate, an elevation in the peak associated with collision-induced uplift, and a shifting forward of the peak time corresponding to the elevation. Overall, variations in Reynolds number significantly influence the vortex flow intensity and evolution of vortex structures at various stages of vortex ring collision. This study demonstrates the deflection, reconnection, and turbulization features of vortex structure evolution based on direct numerical simulations. The partial regulation mechanism of Reynolds number on vortex ring collision is revealed, which is instructive for the study of the evolution mechanism of vortex systems in complex flows.