Spatiotemporal correlation and chaotic dynamics analysis of annular flow with small volume ratio under microgravity

This study focuses on the annular flow payload from the first batch of scientific experiments conducted in 2024 on the China Space Station, investigating its flow and oscillation characteristics under the condition of small volume with a large curved interface. It obtained the laws governing routes to chaos under microgravity: when the volume ratio is 0.525–0.625, the flow mainly follows a quasi-periodic route; when the ratio is 0.625–0.775, the Feigenbaum route with 3n frequency serves as the typical period-doubling route; as the volume ratio increases further, the irregularity of the chaotic route intensifies significantly. During the spatiotemporal evolution of the flow, chaotic routes under different volume ratios were derived via single-point temperature curve analysis, while corresponding flow modes were obtained by integrating modal decomposition techniques—thereby realizing the spatiotemporal correlation between flow modes and chaotic routes. In exploring flow instability mechanisms, this technique (modal decomposition) was used to reveal the core mechanism of subcritical instability, and the characteristics of different volume ratio intervals were clarified: when the volume ratio is 0.525–0.625, the circumferential wave was first observed in the space station; when the ratio is 0.625–0.775, the flow presents a coupled mode with coexisting traveling waves and standing waves. The research findings provide a new perspective and approach for clarifying the chaotic mechanism of annular flow, and lay the foundation for the theoretical refinement and technological advancement in the fields of space fluid mechanics, nonlinear dynamics, and related engineering.