Feasibility of measuring noise sources on a detailed nose landing gear at low cost development Lourenço Tércio Lima Pereira a , Fernando Martini Catalano a , Odenir de Almeida b,⇑ , Paul Bent c a São Carlos School of Engineering (EESC), University of Sao Paulo – USP, São Carlos, São Paulo, Brazil b Experimental Aerodynamics Research Center – CPAERO, School of Mechanical Engineering, Federal University of Uberlandia - UFU, Uberlandia, Minas Gerais, Brazil c The Boeing Company, Saint Louis, MO, USA article info Article history: Received 16 January 2021 Received in revised form 15 June 2021 Accepted 21 June 2021 Keywords: Nose landing gear Aeroacoustics Aerodynamics Aircraft noise Beamforming abstract This work aimed to develop an aeroacoustics analysis of a nose landing gear through rational and low- cost wind tunnel tests to develop potential noise mitigation technologies of aircraft components. This approach led to using a nose landing gear model of the Boeing 777 aircraft, whose more complex parts were 3D-printed. The aeroacoustics and aerodynamics tests were performed in a hard-wall wind tunnel with the capability to perform aeroacoustics tests after corner-vanes and fan section treatment to reduce background noise. Improved beamforming techniques were applied for noise source localization through microphone array measurements. Also, near field noise analysis was performed by microphones installed inside model cavities as part of the correlation procedures for noise investigation and creation of refer- ence data for further CAA simulations. Additionally, using wake-flow mapping and lateral aeroacoustics measurements allowed the characterization of the flow field and noise source positions at low subsonic speeds in the approach condition. The flexibility of the model construction allowed a systematic assem- bly of the main parts and structures, and therefore, a noise build-up analysis showed the contribution of each component to the overall noise of the nose landing gear. Near-field measurements provided better insights into the noise generation mechanisms of each component. Despite some limitations identified by following this approach, the results were consistent and revealed that the noise sources are concentrated in the bay cavity, at the upper structure, and between the wheels. The feasibility of measuring noise sources on a detailed nose landing gear has been achieved with relatively low-cost development, provid- ing useful data for further CAA computations as well as noise mitigation development. Ó 2021 Published by Elsevier Ltd. 1. Introduction Despite all the technological advances found in modern and large transport aircraft, the external noise still concerns authorities and civil institutions. Indeed, aviation authorities establish and apply noise restrictions to aircraft certification and operations [1]. The aeronautic industry has been, for decades, developing means to reduce aircraft noise to comply with these increasingly stringent regulations. First, the considerable noise reduction achieved for the turbofan engines reached, nowadays, the same noise level as the airframe. Therefore, regarding noise, engine opti- mization is no longer the exclusive preoccupation of the aeronautic industry by now. Airframe noise emanating mainly from high-lift systems and landing gears are responsible for the total aircraft noise for approach-to-land operation. Moreover, landing gear noise is dominant for wide-body air- planes, followed by aerodynamic noise originating from deployed high-lift devices, according to [2]. Somehow, landing gear design is primarily driven by the structural and mechanical needs of the parts. Aerodynamics is mostly ignored due to the short interval of exposure to the flow during takeoff, and at landing, the drag is a positive side effect. However, from the aerodynamic standpoint, the flow developing over this complex geometry allows for highly unstable pressure loading and velocity fluctuations. The intrinsic presence of small details such as screws, nuts, pins, hose, and con- nections results in an even more complex flow pattern [3]. There- fore, the difficulty of predicting the sound sources on a landing gear is related to the fact that the geometric details are extremely relevant to the entire problem. Predicting or measuring the landing gear’s noise without considering all the components can lead to large errors in developing technologies for noise mitigation. Therefore, one of the challenges is related to the accuracy of noise measurements of such landing gear devices and how to use https://doi.org/10.1016/j.apacoust.2021.108263 0003-682X/Ó 2021 Published by Elsevier Ltd. ⇑ Corresponding author. E-mail address: odenir.almeida@ufu.br (O.de Almeida). Applied Acoustics 182 (2021) 108263 Contents lists available at ScienceDirect Applied Acoustics journal homepage: www.elsevier.com/locate/apacoust