Characterization of Low Noise Technologies Applied to a Full Scale Fuselage Mounted Nose Landing Gear

Abstract

The reduction of noise generated by aircraft at take-off and approach is crucial in the design of new commercial aircraft. Landing gear noise is significant contribution to the total noise sources during approach. The noise is generated by the interaction between the non-aerodynamic components of the landing gear and the flow, which leads to turbulence generated noise. This research presents results from the European Clean Sky funded ALLEGRA project. The project investigated a fullscale Nose Landing Gear (NLG) model featuring the belly fuselage, bay cavity and hydraulic dressing. A number of low noise treatments were applied to the NLG model including a ramp door spoiler, a wheel axel wind shield, wheel hub caps and perforated fairings. Over 250 far field sensors were deployed in a number of microphone arrays. Since technologies were tested both in isolation and in combination the additive effects of the technologies can be assessed. This study describes the different techniques used to quantify the contribution of each technology to the global noise reduction. The noise reduction technologies will be assessed as a function of frequency range and through beamforming techniques such as source deletion.

Comparing flyover noise measurements to full-scale nose landing gear wind tunnel experiments for regional aircraft

“…To obtain a better understanding of the actual noise emissions of LG systems, wind-tunnel [12,[14][15][16][17] and aircraft flyover experiments [4,9] are typically performed. Whereas the first case offers more controlled flow conditions, it requires the LG model being tested to have a high level of geometric detail to represent the small-scale sound generating mechanisms of the gear [4,5] and it is difficult to replicate the exact conditions present at an aircraft in flight.…”

“…The wind-tunnel experiments were performed under the European Clean Sky funded ALLEGRA (Advanced Low Noise Landing (Main and Nose) Gear for Regional Aircraft) project, coordinated by Trinity College Dublin. This project was developed to assess low-noise technologies applied to a full-scale NLG model [15,16] and a half-scale MLG model [17] of a regional aircraft. ALLEGRA consisted of a consortium of universities (Trinity College Dublin and KTH), an aeroacoustic wind-tunnel company (Pininfarina SPA), and European SME manufacturing and design partners (Eurotech and Teknosud) supported by a leading landing gear manufacturer (Magnaghi Aeronautica).…”

Resonant mode characterisation of a cylindrical Helmholtz cavity excited by a shear layer

“…In practical cases, such as for aircraft take-off and landing where the flow speed varies, it is important to be able to predict these modes so that mitigation measures can be implemented for all modes excited. Recent research published from EU Green Regional Aircraft Clean Sky projects [19][20][21] have demonstrated success in the reduction of nose and main landing gear noise on full and half scale models with the use of low noise technologies. However, the wheel bays continue to be a significant noise source, and for approach and landing, velocities were found to radiate tones at both the Helmholtz resonance frequency of the nose landing gear wheel bay 22 and also at frequencies which were higher than the first, and most typically studied, depth mode for both the nose and main landing gear.…”

Noise Characterization of a Full-Scale Nose Landing Gear

“…There was a bias to radiate upstream for high-amplitude noise centered at 200 Hz, which was believed to be generated by the shear layer impinging on the drag stay and main strut, with contributions in this range from the doors and the steering pinion also. Given the high level of contribution from these components, deployable bay spoilers, such as examined by Dobrynski et al [9] in the RAIN project and Neri et al [40] in the ALLEGRA project, should be given serious consideration for production solutions. The pod gear concepts currently being investigated by NASA also offer great promise to attenuate these noise sources [41].…”