New study paves the way for quieter, fuel-efficient planes

Boundary layer ingesting (BLI) ducted fan test rig inside the aeroacoustics wind tunnel facility at the University of Bristol. Credit: Feroz Ahmed.

Researchers at the University of Bristol have made a significant breakthrough in aircraft design, potentially leading to quieter, more fuel-efficient planes.

Their findings, published in the Journal of Fluid Mechanics, focus on a type of engine known as the boundary layer ingesting (BLI) ducted fan.

Unlike traditional engines mounted under airplane wings, these are partially built into the plane’s body, making them more energy-efficient and now, possibly quieter too.

The study, titled “Aeroacoustics of a ducted fan ingesting an adverse pressure gradient boundary layer,” was led by Feroz Ahmed of Bristol’s School of Civil, Aerospace and Design Engineering, under the guidance of Professor Mahdi Azarpeyvand.

Using the University National Aeroacoustic Wind Tunnel Facility, the team explored how these engines produce and spread sound.

BLI ducted fans pull in air from the front and from the plane’s surface, reducing the effort needed to propel the aircraft and thus saving fuel.

However, understanding the noise they make has been challenging, especially important since reducing noise is key for meeting flight certification standards.

The research team identified several noise sources, including the duct, the rotating fan, and the airflow over the curved airframe.

They discovered that the noise patterns vary with the fan’s thrust. At high thrust, the noise resembles that of traditional fans, but at lower thrust, the duct itself becomes a significant noise maker.

Dr. Ahmed explained that this research fills a crucial gap in our understanding of how noise is generated by engines embedded in the airframe, especially those installed on curved surfaces.

Such insights are essential for designing quieter aircraft, which is increasingly important for both passenger comfort and environmental considerations.

The implications of this study extend beyond traditional aircraft, affecting the design of futuristic flying vehicles like electric vertical take-off and landing aircraft (eVTOLs).

Innovations in this field are being led by projects such as the Bell X-22A, Embraer X, Airbus E-fan, Lilium Jet, Green Jet, and Hybrid Air Vehicle.

Previous studies mostly looked at simpler setups where fans did not have ducts and were positioned over flat surfaces.

The Bristol team’s work advances our knowledge by focusing on more complex, realistic scenarios where fans are embedded in curved airframe surfaces.

This breakthrough not only helps in designing quieter planes but also fuels further research in the field of fluid mechanics, particularly in aeroacoustics—the study of noise generated in airflow, especially in ducted fans dealing with different airflow patterns.

Dr. Ahmed emphasized the broader impact of their findings, stating, “With the growing demand for a pleasant flight experience with minimum environmental impact, there is a need for quieter aircraft.

Our research has potential applications in developing strategies to reduce noise emission in the aviation sector.”

By unlocking the secrets of noise in embedded engines, the team from Bristol is steering significant advancements in aircraft technology, promising a future where air travel is quieter and more efficient.

This study not only provides valuable insights for the aviation industry but also ensures that the skies remain friendlier for both passengers and the environment.