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Study of jet exhaust noise sources and their mitigation through lobed mixers and chevrons

Grage, Danielle L.
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1307323368

Abstract Details

2011, MS, University of Cincinnati, Engineering and Applied Science: Aerospace Engineering.
As regulations to reduce noise pollution become more stringent, understanding the noise sources within jet exhaust and how they can be mitigated is important as jet noise is one of the dominant contributors to the overall acoustic signature of an engine. The objective of this study is to understand the effects two exhaust mixing devises, lobed mixers and chevrons. To this end, three basic configurations were studied: a confluent mixer and nozzle (Confluent), a buried lobed mixer with a circular nozzle (MixerA), and a buried lobed mixer with a chevron nozzle (Chevron+MixerB). The hardware was tested at GE Aviation’s Cell-41 – Anechoic free jet facility. Acoustic data was acquired, as well as flowfield data using Particle Image Velocimetry (PIV). RANS-based (Reynolds Averaged Navier-Stokes) Computational Fluid Dynamics (CFD) analyses were also conducted to complement the test data. Three operating conditions were considered, defined by their shear level, which is a function of the average mixed velocity of the core flow: low shear (80%), nominal shear (100%), and high shear (112%). The results from the PIV and CFD were used for mutual validation and very good correlation was observed for the MixerA configuration with good correlation overall. The acoustic results were consistent with the flowfield analysis, as well as previous studies, and showed that the presence of mixing devices can provide a low frequency acoustic benefit with some modest increase in high frequency noise, due to increasing mixing near the nozzle and reduced turbulence downstream. An additional high frequency noise source was also identified for MixerA at the high shear condition, which was not present for other configurations. This source showed similar features to the High Mach Lift (HML) previously reported by Tester et al and Garrison et al in 2005. It is thought to be the result of shear layer interaction with a normal shock, resulting from localized pockets of supersonic flow that form near the nozzle exit plane. This source was absent for the Chevron+MixerB configuration and more work must be done to better understand the phenomenon.
Ephraim Gutmark, PhDDSc (Committee Chair)
Shaaban Abdallah, PhD (Committee Member)
Jeffrey Kastner, PhD (Committee Member)
126 p.
Aerospace Materials
jet exhaust; lobed mixer; acoustic; chevron; PIV; CFD

Recommended Citations

Citations

  • Grage, D. L. (2011). Study of jet exhaust noise sources and their mitigation through lobed mixers and chevrons [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1307323368

    APA Style (7th edition)

  • Grage, Danielle. Study of jet exhaust noise sources and their mitigation through lobed mixers and chevrons. 2011. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1307323368.

    MLA Style (8th edition)

  • Grage, Danielle. "Study of jet exhaust noise sources and their mitigation through lobed mixers and chevrons." Master's thesis, University of Cincinnati, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1307323368

    Chicago Manual of Style (17th edition)

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