Vortical evolution and instability mechanisms in submersible mixer rotating jets

The vortex evolution and instability mechanisms in rotational jets remain insufficiently understood. This study investigates energy dissipation patterns and vortex evolution mechanisms in submersible mixer rotational jets using improved delayed detached eddy simulation with entropy production theory and vortex identification. The results demonstrate 52.3% of total energy dissipation occurs within five impeller diameters downstream (S1–S5), with available power exhibiting characteristic negative-exponential decay. Vortex instability initiates at z/D = 1, marked by a simultaneous 183% surge in trajectory radius and peak dissipation. Circumferential shear vortices (CSVs) emerge via Kelvin–Helmholtz instability triggered by tip vortex (TV) circumferential velocity. CSV development induces TV short-wave instability, followed by pairing/merging processes forming a single-helical fused tip vortex (FTV). Power spectral density reveals frequency modulation from blade-passing (fBFP) to rotational (fn) frequencies during TV–FTV transition. Crucially, we first identify the FTV govern hub vortex (HV) helical motion through radial pressure gradient modulation. This interaction broadens HV instability modes, triggering helical instability and jet structure oscillations, and causes the peak entropy production observed in region S4, representing a key factor in jet destabilization. The TV–FTV–HV coupling mechanism established in this work provides new insights for energy and stability control in rotational jet systems.