What is it about?
The University of Bristol study explored how boundary layer ingesting (BLI) ducted fans, engines partially embedded in an aircraft, generate noise. A key discovery was the "suction effect" that occurs when these engines are running at high thrust. In this condition, the engines pull strongly on the air from the boundary layer, which is the layer of air close to the aircraft’s surface. This strong suction creates a structured noise pattern similar to non-ducted fan, where the interaction between the fan noise and the ingested boundary layer air is found to be dominant. At lower thrust levels, the suction effect is less pronounced, resulting in a different noise pattern due to the presence of duct noise in addition to fan noise. This study provided insights into how varying fan thrust affects noise production and highlighted the potential of BLI ducted fans to reduce noise emission effectively utilizing the air around the aircraft.
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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: Experimental Identification of Noise Mechanisms Present in a Partially Buried BLI Ducted Fan, May 2024, American Institute of Aeronautics and Astronautics (AIAA),
DOI: 10.2514/6.2024-3419.
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