Improvements of the Beamforming Technique in Pininfarina Full Scale Wind Tunnel by using a 3D Scanning System

Acoustic comfort is a key selling point leading vehicle manufacturers to invest money and resources in research activity. As a consequence the localization of internal and external noise sources of the vehicle is becoming more and more important. The "Beamforming" technique is a well-known method, based on an array of microphones, suitable to identify the external noise sources of a road vehicle. This technique is able to localize the noise sources by estimating the amplitudes of plane, or spherical, waves incident toward the array. For many different reasons, such as the unknown position in the space of the noise sources, the processing time, the algorithm simplicity and so on, the investigation is generally made only on a virtual plane (planar Beamforming) and not in the full three-dimensional space. As a consequence the results accuracy, especially in terms of Sound Pressure Level (SPL) is not entirely satisfactory. Based on these considerations, Pininfarina started a research program to improve the "Beamforming" technique by surveying the three-dimensional geometry of the full scale vehicle placed in the wind tunnel test section. This approach allows for a direct investigation of the noise sources on the 3D model, improving the source detection. The details of the 3D scanning system are described together with its application. Moreover, are presented three experiments that show, with respect to the Planar "Beamforming" (PBF) technique, the improvements of the SPL values of the noise sources detected focusing the microphones array on the surveyed 3D geometry.