What is it about?
Our first-of-its-kind study at the University of Bristol’s National Aeroacoustic Wind Tunnel Facility revealed for the first time how noise is generated and propagated from embedded engines, technically known as boundary layer ingesting (BLI) ducted fans. BLI ducted fans are similar to the large engines found in modern airplanes but are partially embedded into the plane's main body instead of under the wings. As they ingest air from both the front and from the surface of the airframe, they don't have to work as hard to move the plane, so it burns less fuel. We dissected the noise using a source decomposition method into components including fan and duct aeroacoustics and airframe boundary layer flow interactions. The approach provides a clear understanding of the underlying physics of noise origin and variation with different thrust levels of BLI ducted fans.
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Why is it important?
Our study addresses this urgent issue of noise, which poses a major obstacle in obtaining certifications for future aircraft, by uncovering the physics behind the noise these configurations produce. Understanding the noise mechanisms in BLI ducted fans is critical for developing quieter aircraft. With increasing demand for silent aircraft to enhance flight experience with minimal environmental impact, this research could help shape strategies to reduce noise emissions in the aviation sector.
Perspectives
We found that the noise pattern in the BLI or embedded ducted fans changes depending on how much thrust the fan is producing. When the fan is producing high thrust, we observed a noise pattern similar to what is seen in fans without ducts. But when the fan is producing less thrust, the noise pattern changes because the duct itself starts making more noise. By understanding the source of noise from our research, it is hoped that industry can decide what aspects of noise to be controlled and they can make effective noise control devices accordingly.
Dr Feroz Ahmed
University of Bristol
Read the Original
This page is a summary of: Aeroacoustics of a ducted fan ingesting an adverse pressure gradient boundary layer, Journal of Fluid Mechanics, April 2024, Cambridge University Press,
DOI: 10.1017/jfm.2024.134.
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