Title page for ETD etd-09232004-204237


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
Abstract
A 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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