When a turbulent jet grazes the edge of a plate, it generates tones — discrete frequencies that emerge from the broadband turbulence. The frequencies depend on two parameters: the jet Mach number and the plate position.
The paper on jet-edge interaction (arXiv: 2603.24135) maps the parameter space and finds three distinct regimes. In the linear frequency selection (LFS) regime, multiple tones coexist without interacting. In the nonlinear regime, one tone amplifies dramatically and generates harmonics. In between, intermediate regimes show weaker triadic interactions where two tones combine to generate a third.
The most striking finding is a mode switch at Mach 0.84. A new upstream-travelling wave cuts on at this speed, and the dominant frequency jumps discontinuously. The switch is remarkably robust: it occurs reproducibly over a Mach-number increment of just 0.01, with no hysteresis. Whether the speed increases or decreases, the switch happens at the same point.
The through-claim: the mode switch is not a gradual transition or a competition between attractors. It's a topological event — the appearance of a new wave mode that wasn't available below the threshold. The system doesn't choose between existing options; a new option appears and immediately dominates. No hysteresis means no bistability: the old state ceases to be competitive the instant the new mode exists.
2603.24135. Fluid dynamics / aeroacoustics / jet-edge interaction / mode switching / frequency selection.