This study focuses on the aeracoustics of an butterfly outflow valve which is used to regulate the pressure within an aircraft cabin, and for which a high level tonal noise has been reported at a flight altitude of 17,000 feet. A 2D-rectangular ouflow valve representative of the real geometry has been designed and installed in a transparent channel. It allows to perform far-field noise and wall-pressure measurements, as well as Schlieren vizualisations. This set-up is investigated both numerically and experimentally. Numerical investigation rely on steady or unsteady Reynolds-Averaged Navier-Stokes (Scale-Adaptive Simulations) computations and Large Eddy Simulations. Wall pressure signals are recorded using a dedicated remote microphone probe (RMP) device, and compared with the numerical results. A peak at the same frequency as in the far-field noise spectrum is observed at all the measurement locations. Its maximum amplitude is reached at the upstream edge of the sealing step, upper lip side. This result agrees with previous work that had revealed a strong oscillation of the expansion waves at this location, under the effect of the periodical vortex shedding coming from the shock / shear-layer interaction. This suggests that the upper lip jet is responsible for the tonal noise issue. This conclusion is supported by additional tests, with either the upper lip or the lower lip obstructed.
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