Jean-François Piet

AIRFRAME NOISE SOURCE LOCALIZATION USING A MICROPHONE ARRAY

A new phased-array processing method has been developed to achieve accurate two-dimensional localization of acoustic sources. While conventional processing requires a full 2D array with an excessive number of microphones, the present method is designed for sparse arrays, and uses many fewer microphones. A cross-shaped array of 39 microphones was built for wind tunnel testing. The near real-time processing is based on the above method. This is applied to an airframe noise source study on an Airbus aircraft model in the French CEPRA-19 anechoic wind tunnel. The localization maps give an idea of the arrays performance.

Reduction of Landing Gear Noise using Meshes

Acoustic and resistance measurements were performed in NLRs Small Anechoic Wind Tunnel on a large number of meshes intended for landing gear noise reduction. The meshes were tested on generic bluff bodies which simulated single and combined landing gear struts. An out-of-flow microphone array was used to localize and quantify the noise sources on the model. It is found that the meshes yield a drastic broadband noise reduction for a wide range of mesh materials and mesh shapes. The noise reduction occurs for all tested angles of attack and for all tested models. For the combined bodies it is found to be sufficient to treat only the upstream component with a mesh.

Modelling landing gear noise with installation effects

This paper describes continued development and validation of a semi-empirical model of the aerodynamic noise generated by aircraft landing gears at approach. The model has been developed with Airbus funding over a number of years1,2 , but recent studies carried out as part of the EC funded SILENCER project have led to the introduction of a number of new effects that occur on aircraft in flight. The core of the noise model is based on nondimensional source spectra derived from a database of full-scale tests on landing gears installed in the DNW wind tunnel. The new installation effects have been derived using the results of small-scale model tests3 and by analysis of flight test data4. The model is used to examine differences between the performance of noise control fairings installed on a landing gear in a wind tunnel and similar fairings installed on a real aircraft in flight.