Forced Synchronization of Periodic Oscillations in a Gas Column: Where is the Power Source?

Self-sustained oscillations in a gas column induced by a temperature gradient are periodically perturbed by external forcing. In this study, a synchronization bifurcation diagram is mapped out and the power source required to sustain synchronized oscillations is identified using sound intensity measurements. We demonstrate that, even if small forcing entrains the natural frequency or if strong forcing completely suppresses the natural dynamics, the external forcing device is never the source of power; this source resides in the temperature gradient, which creates natural-frequency oscillations.