Aeroacoustic mechanisms explain universal behaviour in high-Mach number cylinder wakes

Recent experimental studies reveal that the near-wake region of a circular cylinder at hypersonic Mach numbers exhibits self-sustained flow oscillations. The oscillation frequency was found to have a universal behaviour. These oscillations are of a fundamentally different nature in comparison with flow oscillations caused due to vortex shedding, which are commonly observed in cylinder wakes at low-subsonic Mach numbers. The experimental observations suggest an aeroacoustic feedback loop to be the driving mechanism of the oscillations at high Mach numbers. An analytical aeroacoustic model that successfully predicts the experimentally observed frequencies and explains the universal behaviour is presented here. The model provides physical insights into and informs us of flow regimes where deviations from universal behaviour are to be expected. These findings hold relevance for a wider class of non-canonical wake flows at high Mach numbers.