Active noise cancellation of ducted fan using real-time acoustic modal analysis

The main objective of this study is to apply active noise cancellation technique to the duct fan. In the acoustic field of a duct fan, the rotating acoustic modes are generated due to the interaction of stators and rotating blades. To achieve the essential elimination of dominant acoustic modes inside the duct, the accurate acoustic mode decomposition and the reproduction of anti-noise are both required. We build a real-time acoustic mode decomposition system with an array of microphones circumferentially mounted on the duct surface. The filtered-x LMS algorithm in the frequency domain form is developed with applying the result of mode decomposition as an error signal in order to achieve the elimination of a specific acoustic mode. An array of loudspeakers is equipped circumferentially onto the duct to generate “anti-noise” signal. A large noise reduction and rapid convergence with this method have been shown by the results.