Localization and Quantification of Rotating Aeroacoustical Sources

In the present work, acoustic imaging methods are developed to determine the locations and strengths of rotating sound sources using a microphone array. The rotating sound sources are associated with specific noise generation mechanisms in the flow field. Therefore, strategies to optimize the blade geometry of wind turbines, axial fans, and aircraft engines can be developed, compared, and evaluated with the aim of noise reduction.

A detailed analysis of the sound fields around rotating sources is carried out in the laboratory and the rotating frame of reference. An acoustic ray method is derived to calculate the sound propagation from sound sources at subsonic and supersonic rotation. In addition, the framework for the localization and quantification of rotating sound sources with a microphone array in terms of signal processing is built. The proposed methods are validated against benchmark test cases and then applied to axial fans and scaled wind turbines to correlate the determined sound source distribution to possible noise generation mechanisms.