Landing gear wake-leading edge flap interaction noise reduction through the use of porous screens.

Abstract

This thesis focuses on the optimum characteristics and location of a porous screen, to reduce wing leading-edge noise produced by the wake of a landing gear impinging on a wing downstream. The aim is to identify, from the two different types of porous screens tested (perforated plate and woven wired mesh) with different open areas, which is the one that reduces wing leading-edge noise the most. In terms of location, the aim is to identify where is the optimum location between the landing gear and the wing to install the optimum porous screen. An experimental set-up that consists of a main landing gear, landing gear cavity and a wing downstream was designed, manufactured and tested. This setup was able to produce wing leading-edge noise by measuring an increase in noise at a relatively low frequency, in accordance with
Amiet’s leading-edge noise model. With the increased blockage of the porous screens, the velocity deficit increased downstream of the screens. The turbulent intensity and integral length scale also increased. Screen self-noise was identified at a relative high frequency range (above 6 kHz). The frame that supports the porous screens generated self-noise in the mid frequency range (between 1 and 6 kHz). The optimum porous screen for reducing wing leading-edge noise was the 60% open area woven wire mesh. This screen was the one that most reduces the velocity impinging on the wing leading edge with the least increase in turbulent intensity and integral length scale due to the flow through the screen itself. This is consistent with wing leading-edge noise being
a dipole noise source in which reductions in local velocity has an impact on the noise generated. The optimum location to install the frame for wing-leading edge noise was closest to the landing gear. The mechanism responsible for this was, at the furthest location from the wing, less turbulent wake is directed into the wing, and it is not introducing new noise sources into the wing’s leading edge due to frame trailing edge flow separation. Frame self-noise was greater when is installed closer to the landing gear and reduced when moved downstream near to the wing. The landing gear wake impinges in several locations on the frame with higher energy the closer the frame is to the landing gear. Frame design and integration was shown to be important for the overall noise reduction.

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Identifiers

ORCID for Francisco Javier Martinez Lara: orcid.org/0009-0007-6923-2431

ORCID for Zhiwei Hu: orcid.org/0000-0001-6737-4363

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