Jeffrey O'Brien

Effects of Nozzle Helmholtz Number on Indirect Combustion Noise by Compositional Perturbations

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Investigation of the mechanisms of jet-engine core noise using large-eddy simulation

As further reductions in aircraft engine noise are realized, the relative importance of reducing engine-core noise increases. In this work, a representative engine flowpath is studied to examine the mechanisms by which direct and indirect core noise propagate through the engine and affect the far-field sound radiation. The flowpath consists of a model combustor, a single-stage turbine, a converging nozzle, a near-field jet, and far-field acoustic radiation. A combination of high-fidelity simulations and low-order semi-analytic models is used to represent the generation and propagation of disturbances through the flowpath. Particular details are provided for LES calculations of combustion chamber, nozzle exhaust flow, and jet noise radiation. A one-way coupling procedure is employed for propagating disturbances from one stage of the calculations to the next, and the results show substantial changes in the far-field sound directivity and frequency spectra due to fluctuations generated by the upstream engine core.

Linear Analysis of Jet-Engine Core Noise Based upon High-Fidelity Combustor and Turbine Simulations

As further reductions in aircraft engine noise are realized, the relative importance of engine core noise increases. In this study, a computational framework for examining indirect core noise is proposed, consisting of a representative engine flow-path containing a model gas turbine combustor, a single-stage turbine, a converging nozzle, and free-field radiation. Combined high-fidelity and lower-order simulation techniques are used for each component of the modeled engine. Preliminary, uncoupled results from the combustor and turbine are presented as well as the nozzle-flow simulations. Particular attention is paid to the verification and performance of a linearized Euler solver for predicting the subsonic heated jet flow as well as its far-field acoustic radiation. Two relevant verification tests are shown as well as the nozzle’s response to time-harmonic excitations in both the presence and absence of the mean jet flow over a range of Strouhal numbers. Future work will include coupling the simulations and a more detailed analysis of the mechanisms of core-noise generation and propagation.