An aeroacoustic study of a leading-edge slat: Beamforming and far field estimation using near field quantities

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Kyle A. Pascioni
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The leading edge slat of a high-lift system is a large contributor to the overall radiated acoustic field from an aircraft during the approach phase of the flight path. This is due to the unsteady flow field generated in the slat-cove and near the leading edge of the main element. In an effort to understand the noise-source mechanisms, a suite of experimental measurements has been performed on a two-dimensional multi-element MD-30P30N airfoil, including PIV, steady and unsteady surface pressure, and phased microphone array measurements. Acoustic trends are given with angle of attack and flow speed which corresponds to a stowed chord Reynolds number range of 1.2 × 106 ≤ Rec ≤ 1.71 × 106. Spatially integrated beamforming is used to isolate the slat noise, while Kevlar sidewalls are utilized to minimize environmental influence. In addition, temporally-resolved estimates of a low-dimensional representation of the velocity vector fields are obtained through the use of proper orthogonal decomposition and spectral linear stochastic estimation and show good agreement with independent phase-locked PIV measurements. A time-resolved estimate of the pressure field is then computed via solution of the pressure Poisson equation. From this, Curle's acoustic analogy scaled for the frequency-dependent spanwise coherence length projects the time-resolved pressure forces in the slat region to the acoustic far field for comparison to the array measurements. The favorable results establish the connection between the dominant unsteady flow structures most responsible for the radiated noise and provide insight for future noise reduction efforts.
Journal of Sound and Vibration
1 September 2018
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