What is it about?

This study explored how the interaction between airflow and noise generation in electric embedded engines, specifically Boundary Layer Ingesting (BLI) ducted fans, affects human perception of noise in future aircraft. 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 being mounted under the wings. The study dissected the problem into three main areas (or physics): aerodynamics, aeroacoustics, and psychoacoustics. The study investigated how the interaction between three physics changes under different fan thrust levels and operating conditions, and examined how they influences human annoyance. The detailed analysis provided a clear understanding of the underlying physics of noise origin and human annoyance and their 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 and annoyance associated with BLI ducted fans. The findings indicate that both duct and fan noise must be considered in low- and high-thrust levels during the design of noise control devices. This integrated approach aims to provide valuable insights for developing advanced noise reduction strategies and enhancing the human acoustic comfort of next-generation aircraft.

Perspectives

According to the European Commission's Flight Path 2050 (FP2050) challenge, by 2050, future commercial aircraft are expected to cut carbon emissions by 75% and noise emissions by 65%. These ambitious targets signify a major shift towards more sustainable aviation technologies, with a focus on reducing the environmental impact of flying. Achieving these goals will require substantial changes in airframe design and propulsion systems, highlighting the need for green aviation innovations. One promising solution to these challenges is the adoption of electric propulsion systems, particularly within the Urban Air Mobility (UAM) sector. Concepts like electric vertical take-off and landing (eVTOL) vehicles and distributed electric propulsion (DEP) systems represent significant progress towards meeting these environmental targets. Additionally, ducted fan systems, including Boundary Layer Ingesting (BLI) designs, offer potential pathways to achieving these reductions. However, while electric UAM systems promise lower carbon emissions compared to traditional fossil fuel-powered aircraft, noise emissions remain a significant challenge. The psychoacoustic annoyance caused by these systems, especially with their frequent urban operations, affects both human health and wildlife. Thus, even with advancements in emission reduction, addressing noise is crucial. Developing technologies to lower noise levels and psychoacoustic annoyance is essential for obtaining vehicle certifications and ensuring the successful adoption of these new aircraft technologies. The insights from our study into how airflow, noise generation, and human perception interact in BLI ducted fans provide a critical basis for advancing quieter and more efficient propulsion systems, contributing to the broader goal of sustainable aviation.

Dr Feroz Ahmed
University of Bristol

Read the Original

This page is a summary of: Boundary Layer Ingestion Ducted Fan: Aeroacoustic and Psychoacoustic Insights, May 2024, American Institute of Aeronautics and Astronautics (AIAA),
DOI: 10.2514/6.2024-3379.
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