Hybrid modeling of engine core noise
Abstract/Contents
- Abstract
- Core noise, or the noise generated by unsteady combustion, is a growing concern for aircraft engine designers. Core noise is typically divided between direct noise, the acoustic fluctuations generated by the flame, and indirect noise, the noise created as unsteady flow structures are distorted and accelerated downstream of the flame. This thesis develops new modeling tools for predicting both direct and indirect noise behavior and also analyzes the mechanisms by which core noise arises. The problem of indirect noise generation in turbomachinery applications is considered in detail. Existing low order, acoustically compact models for indirect noise prediction are reviewed. A new correction to the compact model is then proposed which renders new predictions rotationally invariant, a property that previous models do not possess. Ultimately, an acoustically noncompact model is developed which incorporates geometric and frequency-dependent effects and and is compared against higher order numerical results. It is then demonstrated that fluctuations in mixture composition can act as a previously unconsidered source of indirect noise. Additionally, the sensitivity of the mechanism to fuel choice and thermodynamic operating considerations is explored. The model is then expanded to account for acoustically noncompact effects in nozzle flows. Lastly, the impact of core noise on the total downstream acoustic signature of an aircraft engine is examined. The study focuses on a representative engine flowpath, constructed of a test stand combustor, single stage turbine, nozzle, jet and acoustic farfield. The modeling approach couples high fidelity Large Eddy Simulation of the combustor, nozzle and jet with low order models for the turbomachinery stages in order to capture both the generation and propagation of acoustic and turbulent fluctuations as they pass from the combustor downstream to the acoustic farfield of the device. It is found that the coupling between core noise and jet noise is quite complex, with low frequency sound amplified by core noise effects while high frequency noise is slightly suppressed. Ultimately, a physical mechanism for this coupling is proposed, positing that the presence of upstream fluctuations excites an instability in the jet, leading to the observed changes in acoustic response.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2017 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | O'Brien, Jeffrey D |
|---|---|
| Associated with | Stanford University, Department of Mechanical Engineering. |
| Primary advisor | Ihme, Matthias |
| Thesis advisor | Ihme, Matthias |
| Thesis advisor | Lele, Sanjiva K. (Sanjiva Keshava), 1958- |
| Thesis advisor | Moin, Parviz |
| Advisor | Lele, Sanjiva K. (Sanjiva Keshava), 1958- |
| Advisor | Moin, Parviz |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Jeffrey D. O'Brien. |
|---|---|
| Note | Submitted to the Department of Mechanical Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2017. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2017 by Jeffrey Daniel O'Brien
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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