Analysis of noise source mechanisms for a subsonic jet

Abstract

Despite advances in engine design, from high bypass to co-axial or lobe shaped nozzles, the problem of jet noise reduction continues to require ongoing research in order to comply with the criteria inherent in environmental objectives set out by relevant bodies worldwide. Fundamental to this work, will be a clearer understanding of the generation and propagation of noise sources in subsonic jets. In this regard, it is the aim of this thesis to identify and examine noise source mechanisms from a subsonic jet. The correlation between the velocity fluctuations inside the jet and the near-field acoustic pressure is measured and a multiple input / multiple output model is implemented. This identifies how each source, independent of all others, propagates and radiates into the near-field. Through the use of dedicated testing, specifically designed to extract information on source propagation, techniques such as those proposed in this work will lead to further understanding of how source terms behave in a subsonic jet.