International audienceOn commercial aircrafts, the adequate pressure ratio between the cabin and the exterior is regulated with circular outflow valves. At an operating pressure ratio equivalent to 17000ft in altitude, a tonal noise is observed at 11kHz and higher harmonics. A feedback loop is believed to be responsible for this tonal noise and it is studied on an extruded two-dimensional mock-up representative of the outflow valves including the sealing steps. A spectral analysis is performed on the Schlieren images in terms of pixel intensity for each pixel independently. This accentuates the aliasing phenomena of the higher harmonics when studying the maximum power spectral density. In order to highlight different patterns in the flow, phase maps are computed with respect to a particular pixel at 11kHz and harmonics. Last, the feedback mechanism is visible between the sealing step and the valve with the application of a novel wavelet-based technique on the Schlieren images
