Aeroacoustics coupling of a misaligned jet-slot-oscillator with non-planar modes of a resonator

The impingement of a plane jet on a slotted plate produces a “jet-slot oscillator” emitting acoustic
tones. The coupling of such tones with high-order acoustic resonances of the flow-supply duct
(i.e., above the first transverse mode cut-off frequency) is studied experimentally , in the particular case where the jet-exit and the obstacle are misaligned in the spanwise direction. An experimental set-up based on microphones and hot-wire probes is used to investigate the effect of the slot angle on the sound production mechanism. The aligned jet-slot oscillator is first studied, showing that the parallelism between the jet exit and the slot imposes the excitation of planar modes of the resonator only. Conversely, the misaligned jet-slot oscillator appears to be coupled with a combination of planar and transverse modes. The induced spanwise variation of the acoustic field phase has two consequences. First, it compensates the difference of vortices convection time in the spanwise direction, due to the obstacle misalignment. Second, it enhances the spanwise coherence of the aeroacoustic source produced by the jet-slot interaction: the vortex-tubes are shed in an oblique direction which tends to be parallel to the obstacle.