Within NOISETTE, Cenaero and VKI combined their respective expertise in computational fluid dynamics and acoustics in order to deliver a tailored solution for the aero-acoustic assessment and design of a low-noise configuration for a regional aircraft nose landing gear. The computational approach relied on performing high quality detached eddy simulations and on using the obtained noise sources for acoustic propagation.
The Clean Sky JTI-GRA NOISETTE project was funded by the EU seventh Framework Program (grant agreement number 271886) and answered the call for proposal JTI-CS-2013-3-GRA-02-012. This 7-month project was dedicated to the development of a tailored solution for the aeroacoustic assessment and design of a low-noise configuration for a regional aircraft nose landing gear. The computational approach relies on performing high quality detached eddy simulations and on using the obtained noise sources for acoustic propagation.
For modern high-bypass engine powered commercial aircraft, the airframe noise represents the main contribution to the overall flyover noise levels during landing approach phases. Five main mechanisms are recognized to contribute significantly to the airframe noise:
- the wing trailing-edge scattering of boundary-layer turbulent kinetic energy into acoustic energy;
- the vortex shedding from slat/main-body trailing-edges and the possible gap tone excitation through nonlinear coupling in the slat/flap coves;
- the flow unsteadiness in the recirculation bubble behind the slat leading-edge;
- the roll-up vortex at the flap side edge;
- the landing-gear multi-scale vortex dynamics and the consequent multi-frequency unsteady force applied to the gear components.
The present project addresses the last mechanism that is relevant to JTI-CS- 010-3-GRA-02-012 through a proper simulation approach.
For this purpose, two research centers, Cenaero and the von Karman Institute for Fluid Dynamics have combined their respective expertise in computational fluid dynamics (CFD) and computational acoustics (CA) in order to deliver a tailored solution for the aeroacoustic analysis of nose landing gear low-noise configurations for a regional aircraft. Firstly, it aims at performing the aeroacoustic analysis of a baseline geometry designed by Messier-Bugatti-Dowty and Alenia. The purpose of the study is to provide the most comprehensive view on the critical components of the NLG assembly on the emission of noise. Secondly, based on the outcomes of the noise analysis of the baseline geometry, two low-noise configurations have been defined in agreement with the constraints defined by the end-user (CIRA) as the best noise mitigation strategy.
The first design focuses on the upper part of the landing gear whereby adjusting the front door of the bay opening a spoiler is formed. The second design focuses on the lower part and develop the low noise configuration using the add-on fairing. In this design, the landing gear is equipped by four caps to cover the rims’ cavities and a windshield between two wheels.
Despite the possible combination of both designs, here it has been preferred to investigate the performance of each one individually.
The total OASPLA levels accounting for all components considered have shown improvements on the acoustic field of around 4 dBA for the 1st low-noise configuration and 2 dBA for the 2nd low-noise configuration at the observer array.
The two proposed designs have been selected by the ITD-GRA consortium for the full-scale wind-tunnel tests which will be performed within the ALLEGRA project in 2014.