|Title:||Active noise control for fan duct|
|Subject:||Fans (Machinery) -- Noise|
Hong Kong Polytechnic University -- Dissertations
|Department:||Faculty of Engineering|
|Pages:||xi, 96 pages : color illustrations|
|Abstract:||An active approach targeting blade pass frequency (BPF) tones from an axial fan was investigated. The approach involved the installation of an axial fan into a short duct with narrow-band active noise control functions. First, a general description of active noise control systems is presented including theoretical analysis of sound propagation in finite-length ducts, the characteristics of noise source, and the typical structure of control systems. Next, the characteristics of the Filtered-X Least-Mean-Square (FXLMS) control algorithm were investigated by simulation. The simulation results indicated that the convergence speed will increase with larger stepsize and filter order within an appropriate range. The experimental validation of the noise control approach was also performed. A simple noise source with single channel active noise control system was used to validate the characteristics of a control system with control performance of broadband noise source and narrow band noise source and optimal placement of the error sensors and control loudspeaker. Next, the narrowband active noise control system with rotation speed reference signal was implemented to target the BPF tones of the practical fan duct. Experimental results showed significant noise reduction of 30 dB in BPF tones and 2.7dB for the overall fan noise level. Additionally, experiments were performed to validate the duct effect for overall noise level, determine the airflow effect on the error microphone, and to test the application of multi-channel active noise control for higher order BPF tones.|
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