Intermittency route to chaos in a forced globally unstable jet*

We explore the universal transition to chaos in a prototypical hydrodynamic oscillator, namely a globally unstable low-density jet subjected to time-periodic acoustic forcing. We find that as the forcing strengthens at an off-resonant frequency, the jet exhibits a sequence of nonlinear states: a period-1 limit cycle $ ightarrow$ $mathbb{T}^2$ quasiperiodicity $ ightarrow$ intermittency $ ightarrow$ deterministic chaos. We confirm the existence of chaos through the 0--1 test, the correlation dimension, and the horizontal visibility graph. We then show that the intermittency obeys type-II Pomeau--Manneville dynamics by analyzing the first return map, the recurrence plot, and the scaling laws of the quasiperiodic epochs between successive bursts of chaos. By providing experimental evidence of the type-II intermittency route to chaos in a globally unstable jet, this study reinforces the notion that strange attractors emerge via universal mechanisms in open self-excited flows. This discovery paves the way for the development of instability control strategies based on chaos theory.