Feedthrough between two successive cylindrical water–air interfaces in divergent geometry

This study experimentally and theoretically investigates the feedthrough between two successive cylindrical water–air interfaces under divergent expansion. Three initial conditions are examined: interfaces initially in-phase and anti-phase, and an initially unperturbed outer interface. Amplitude measurements reveal that the feedthrough depends on the initial perturbation phase difference, thereby altering the instability evolution of both interfaces. A linear theory is developed for cylindrical fluid layers, accounting for surface tension and cylindrically divergent (outward-expanding) geometry, and agrees well with experiments in the near-unity Atwood number regime. Dimensionless feedthrough efficiency factors derived from the linear theory demonstrate that the interface coupling is determined by the radius ratio of two interfaces, interface acceleration, and perturbation wavenumbers. Notably, under extremely high acceleration (as a theoretical limit of our model), the feedthrough is predicted to stabilise both interfaces. This trend, if it persists under compressible conditions, could have implications for inertial confinement fusion. These results provide critical guidance for instability manipulation in both radially convergent and radially divergent geometries.