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Engineering

Research project: Determining aircraft engine combustion noise from acoustic imaging measurements.

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Future aircraft engine designs will have lower emission combustors but this needs to be achieved without significantly affecting aircraft noise levels. When a new low emissions combustor is tested at full-scale, the image processing aims to clearly separate out the combustion noise from the other sources, especially from the jet which radiates over a similar frequency range to that of combustion noise.

The basic approach is to process far-field cross-spectral density (CSD) data from a static engine test with a non-linear least-squares (NLS) technique and a source model to determine the 1/3-octave spectrum source levels at each angle, or ‘source breakdown’. The CSD data can be simply Fourier transformed to obtain a source image but the NLS/source model process is required to obtain a quantitative source breakdown. The main achievement has been the development of a post-processing code, called the ‘AARC funded ISVR directional source-breakdown (AFINDS)’, that offers a robust method of obtaining the source breakdown at 90° to each source and its directivity normalised to that angle. This improves on previous work which assumed that all the sources had the same or a similar directivity.

Funding this work is being conducted in collaboration with Prof S A L Glegg (Florida Atlantic University) and is funded by the Aeroacoustics Research Consortium, which includes Rolls-Royce plc and the Boeing Company.

Related research groups

Acoustics Group
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