Author ORCID Identifier
https://orcid.org/0009-0007-6902-7948
Date Available
7-4-2024
Year of Publication
2024
Document Type
Doctoral Dissertation
Degree Name
Doctor of Philosophy (PhD)
College
Engineering
Department/School/Program
Mechanical Engineering
Advisor
Dr. David W. Herrin
Abstract
Vibro-acoustic energy propagates through heating, ventilating, and air conditioning (HVAC) systems through both airborne and structureborne paths. In this research, measurement and simulation studies are performed to better understand this propagation of energy and how to better attenuate the sound before it impacts building occupants.
First, a scaled-down experiment was developed to assist in the validation of numerical simulation models. A small source room was attached to a wooden duct with variable cross-sectional area. The sound power for both untreated and treated ductwork was measured using sound intensity scanning, and the insertion loss is the difference between untreated and treated cases. In conjunction with the measurement study, finite element simulation was used to simulate the acoustical energy path. Four different studies were then performed.
In the first study, the insertion loss of large aspect ratio duct cross-sections with glass fiber lining was measured using the experimental setup. An acoustic finite element simulation was developed for predicting insertion loss, and simulation results agreed well with measurement. Using the validated finite element simulation model, the effects of varying the duct cross-section and liner thickness were assessed. Simulation results demonstrate that insertion loss is highest when the smallest cross-sectional dimension is on the order of one acoustic wavelength. In addition, the insertion loss can be substantially improved by adding thickness to the lining along the longest cross-sectional dimension.
In the second study, measurement and simulation were used to investigate the impact on insertion loss of adding a foil scrim layer to the sound absorptive lining. It was demonstrated that a scrim or mass layer can significantly improve the attenuation at low frequencies so long as mass layer is pinned to the glass fiber. If an adhesive is placed between the mass layer and glass fiber, the beneficial impact of the mass layer is compromised.
The third study investigated the insertion loss performance of microperforated panel sound absorbing baffles. These baffles consist of two microperforated panel layers with a honeycomb structure between layers. Measurement and simulation were used to better understand the microperforated panel baffle absorber functionality. The insertion loss results demonstrate the absorbers excellent performance, and that the frequency of maximum attenuation can be controlled by changing the baffle thickness.
In the final study, sound propagation from a duct was simulated, and the results were compared with archival data from two other laboratories. The simulations showed good correlation with measurements for both unlined and lined ducts with rectangular cross-sections. Rectangular unlined ductwork is of particular interest due to its poor breakout transmission loss. However, significant discrepancies were observed between measurements and predictions for circular cross-sections, likely because of the high breakout transmission loss. It is suspected that environmental noise in the lab compromised the measurements.
Digital Object Identifier (DOI)
https://doi.org/10.13023/etd.2024.255
Funding Information
This study was supported by the Vibro-Acoustics Consortium.
Recommended Citation
Li, Caoyang, "PROPAGATION OF VIBRO-ACOUSTIC ENERGY IN DUCTS: MEASUREMENT, SIMULATION, AND ATTENUATION STUDIES" (2024). Theses and Dissertations--Mechanical Engineering. 222.
https://uknowledge.uky.edu/me_etds/222
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