Author: Hui, Chun Wai Eugene
Title: Optimization of micro-perforated cylinder under acoustics and fluid flow consideration
Degree: M.Eng.
Year: 2018
Subject: Hong Kong Polytechnic University -- Dissertations
Air ducts -- Acoustic properties
Noise control
Fluid dynamics
Department: Department of Building Services Engineering
Pages: ix, 100 pages : color illustrations
Language: English
Abstract: This research investigate the acoustics performance of Micro-perforated cylinder for in duct application. The cylinders were inserted in a rectangular duct and measured with stationary and moving medium condition. The acoustics performance of the cylinder were contributed by two properties. Which are Bragg Band Gap and sound absorption of Micro-perforation. The research quantify the acoustics performance of Micro-perforated cylinder by both simulation and experiment. Simulation were used to quantify the acoustics performance and the fluid flow resistance of the cylinder array. Experiment were conducted to validate the simulation result. The simulation of the cylinder includes two parameters the first one is Transmission Loss, used to quantify the acoustics performance. The second one is Local Loss Coefficient, which used to quantify the pressure drop when the fluid flow through the cylinder layers. The experimental setup includes test rig which fixed in-duct cylinder location, anechoic termination and fan were connected for experimental validation. Other devices included pulse analyser, signal generator, amplifier, speaker and microphones were also being applied for the experiment. The result from the experiment showed alignment with the simulation result. It is found that although the Transmission Loss for frequency higher than first cut-off frequency is different between simulation and measurement, but the simulation results a good trend prediction. The increase of medium flow velocity would decrease the effects of Transmission Loss. However, the decrease start becoming significant when the velocity is larger than 10 m/s. It is also found that the spacing of 80 mm between two microphones gives a best resolution measurement result when using two microphone measurement. The acoustics performance of Micro-perforated cylinders were effective as proven by both simulation and experiment result.
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Please use this identifier to cite or link to this item: https://theses.lib.polyu.edu.hk/handle/200/9718