Type of Document Dissertation Author Homma, Kenji URN etd-09232004-204237 Title Compact Integrated Active-Passive Approach for Axial Fan Noise Control Degree PhD Department Mechanical Engineering Advisory Committee
Advisor Name Title Fuller, Christopher R. Committee Chair Baumann, William T. Committee Member Inman, Daniel J. Committee Member Johnson, Martin E. Committee Member Leo, Donald J. Committee Member Keywords
- axial fan noise
- active-passive control
- sound propagation in ducts
Date of Defense 2004-09-17 Availability unrestricted AbstractA new active-passive approach for the control of noise radiated from a small axial fan
was investigated. The approach involved the installation of an axial fan into a short duct
with both passive and active noise control functions. First, a systematic methodology for
the analytical modeling of finite-length ducts with multiple discontinuities was
formulated. The procedure involved the modeling of a duct as a collection of simple duct
sections, which were interconnected at multiple junctions.
Analytical studies have shown that a short lined duct provides passive noise
reduction effects through the mass-loading effect of the duct air volume at low
frequencies and the sound absorption by a passive liner at high frequencies. It was also
shown that active control can provide further noise attenuations at low-to-mid
frequencies, thereby enhancing the overall noise control performance. Two alternate
designs of active-passive noise control fan duct were considered. One was a simple non-
segmented duct with a 2x2 active control and the other was an internally segmented duct
with an 8x8 active control. It was indicated that the latter design possesses a significantly
higher global noise control potential than the former with respect to both bandwidth and
attenuation level. This was attributed to the reduction of the unwanted pressure
contributions from the duct cross modes through the high frequency shifting of the
associated cut-on frequencies.
The experimental validation of the noise control approach was also carried out.
An active-passive noise control fan duct incorporating the segmented duct design with
8x8 active control was constructed in conjunction with a hybrid feedforward-feedback
control system. Experimental results have shown significant reductions in the total fan noise power associated with the first four BPF tones by the feedforward control and the
broadband fan noise power by the feedback control. The overall active-passive noise
control characteristics were observed to be in accordance with the analytical results.
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