2021 Volume 38 Issue 2 Pages 380201-
In the so-called modern linear stability analysis based on a spatial evolution model, the origin of unstable wave responsible for spontaneous liquid jet disintegration is attributed to an infinitesimal amplitude of perturbation inevitably introduced within an injector. This implies that the jet disintegration is a one-way process caused by an almighty noise. Against this belief, author’s research group conducted ISS experiments, in which a microgravity plug-flow jet, assumed in the classical Rayleigh’s analysis, was realized in order to validate our proposal that any liquid jet can spontaneously disintegrate thanks to a self-destabilizing causality loop formation along the jet. Unlike the modern linear stability analysis prediction, covenctively unstable waves observed for all jet issue speeds tested had the phase velocity equal to the jet velocity, and they played an important role to result in various quasi-steady jet disintegration states. This paper first examines why the noise concept was necessary in the modern linear stability analysis, and then presents the 1D jet model numerical simulations which support our experimental observations and reveal their underlying physics. It is found that the spatial evolution model does not describe the physically reasonable unstable wave formation process even for a forced jet such as an ink-jet printer.