Landing gear noise control using perforated fairings

Abstract

Landing gears of commercial aircraft make an important contribution to total aircraft noise in the approach configuration. Using fairings to shield components from high speed impingement reduces noise. Furthermore, perforating these fairings has been confirmed by flight tests to further enable noise reduction. Following an earlier fundamental study of the application of perforated fairings, a study has been performed to investigate and optimize the benefits of bleeding air through landing gear fairings. By means of wind tunnel tests, an aerodynamic and acoustic survey has been performed on a simplified generic main landing gear to explore the influence of (perforated) fairings on the lower part of the gear. The results show that for this specific case, the application of impermeable fairings reduces noise in the mid-and high frequency range by shielding sharp edged components from high velocity impingement. However, below 1 kHz the noise is shown to increase significantly. Application of the perforations is shown to diminish this low frequency increase whilst maintaining the reduction in the mid-and high frequency range. The aerodynamic and acoustic measurements point in the direction of the separated flow of the fairings interacting with the downstream gear components responsible for the low frequency noise increase. Bleeding of the air through the fairings reduces the large scale turbulence in the proximity of these components and hence diminishes the low frequency noise increase.

Numerical Investigation of Active Flow Control using Steady Blowing for Landing Gear Noise Reduction

“…5 Therefore, successful flow control methods for landing gear noise reduction must tackle both the bluffbody self-generated noise and the unsteady interaction noise between various landing gear components. Passive flow control methods, such as the application of solid or perforated fairings have been employed 6,7 in the past. The large bluff components like the bogie area and the torque link can be covered with a fairing to reduce both the self-noise and the interaction noise.…”

Numerical simulation and experimental research on aerodynamic noises of the single wheel landing gear in an aircraft

“…When an aircraft parks and keeps its flap closed, landing gear noises can be 25 % of aircraft noises [3]. However, experimental research and numerical simulation become very difficult due to many factors including the complex geometric shape of landing gear, strong interaction with fluids [4,5], wide-range acoustic band, wide spreading range, and relatively low energy. So far, the problem of landing gear noises has still been one of difficulties in studying airframe noises.…”

On the Contribution of Individual Landing Gear Components to Landing Gear Loads and Noise

“…Initial noise reduction solutions included the application of solid or perforated fairings 15,16 which prevented the impingement of high speed flow on the downstream landing gear components. These passive devices concentrated on the bogie area, where it is feasible to cover the non-aerodynamic components.…”

“…The aerodynamic and aeroacoustic measurements on a 1/4 scale simplified main landing gear model, previously used by Boorsma et al, 15 were conducted in the wind tunnels of the University of Southampton. The major components constituting the model were interchangeable, thus allowing the application of an incremental approach.…”

“…The torque arms were set as part of the bogie assembly and thus were not interchangeable. The articulated link, that was previously attached to the main strut and bogie, 15 was omitted to allow rotation of the bogie in the range of inclination angles α between 40…”