Investigations of flow structures and dynamical behaviors of steam jet condensation in crossflow based on dynamic mode decomposition and proper orthogonal decomposition

Despite its significant scientific and technological importance, the multi-scale vortex structure and dynamical behavior induced by the direct contact condensation of steam jets in flowing water is an unresolved problem in classical energy and power systems. This study elucidates the dynamics of dominant flow structures through integrated high-speed visualization, dynamic mode decomposition (DMD), and proper orthogonal decomposition (POD) analyses. DMD extracts uncoupled coherent structures with specific dynamical modes and frequencies, while POD hierarchically resolves dominant energy-containing structures. Comparative analysis of DMD and POD modes, combined with growth rate and time coefficient evaluations, reveals that unstable condensation regimes are dominated by collapse modes. Conversely, the shear-layer mode predominates in the Stable regime. POD-based flow field reconstruction demonstrates superior accuracy compared to DMD, requiring significantly fewer modes in the Stable regime due to the high energy of the time-averaged flow field. Notably, the Chugging regime, characterized by prolonged intermittent plume-less eruptions, exhibits concurrent high energy of the time-averaged flow field and flow instability characteristics.