"This work first investigates the effect of manufacturing tolerances on realized attenuation for two degree-of-freedom linings with the use of lining models and finite element duct propagation codes. Acoustic linings were created for two turbofan engines that optimize attenuation at takeoff/sideline and approach conditions. Lining physical and geometric parameters were set, which best meet the optimum impedance requirements at two target frequencies. Similar linings were created to investigate sub-optimum designs. Variations of these parameters representing realistic manufacturing tolerances were used to systematically examine the effect on installed impedance and predicted attenuation. Attenuation at sideline and approach conditions was found to be sensitive to manufacturing tolerances around optimum conditions. The results of the study are case dependent; however the analysis scheme presented provides a method for cost-benefit analysis of manufacturing processes. In a second study, an impedance tube, with an associated data analysis method, was developed and analyzed for temperature uncertainties that allowed the measurement of impedance of acoustic samples at elevated temperatures. This impedance measurement method was validated at room temperature by comparing the results with predicted impedance from empirically based impedance models and with impedance measurements in a standard traversing microphone impedance tube. Impedance for four samples was measured at elevated temperatures, and the results were compared to room temperature measurements. For two of the samples, the impedances measured at elevated temperatures were compared to the results of extensions of room temperature empirical models, confirming the trend of the results of the elevated temperature measurements"--Abstract, page iv.
Le, Vy Khoi
Landers, Robert G.
Mechanical and Aerospace Engineering
Ph. D. in Mechanical Engineering
Spirit Aerosystems Inc.
Missouri University of Science and Technology
Journal article titles appearing in thesis/dissertation
- Normal incidence impedance measurement at elevated temperatures
xvi, 160 pages
© 2010 David R. Burd, All rights reserved.
Dissertation - Open Access
Absorption of sound -- Testing
Airplanes -- Turbofan engines
Noise control -- Testing
Print OCLC #
Electronic OCLC #
Link to Catalog Record
Burd, David R., "Effects of optimized and sub-optimum two degree of freedom lining tolerances on modeled inlet acoustic attenuation and normal incidence impedance measurement at elevated temperatures" (2010). Doctoral Dissertations. 2161.