Why the technology of emerging electric motors seems so boring – and how to fix it

Scientists from the University of Bristol in collaboration with the University of Salford have discovered the deep cause behind the particularly irritating noise produced by the engines with limit layer ingestion (BLI) – key technology in future electric and hybrid planes.

Rely on previous work who identified the general noise Sources in BLI Systems, this last search, published In ACOUSTICS NPJDive more deeply into the physics of the generation of its aerodynamics, revealing how the turbulent boundary layer flow interacts with the components of rotating fan and duct to produce two distinct and perceptual acoustic signatures.

The key to this research is an assessment based on fluid mechanics which discovers the fundamental aerodynamic origin of two different types of large -band noise models, called spectral characteristics of “hay” which affect the way the noise is perceived.

In acoustics, the “hay back” describes the effect of turbulent flow Distributing the tone sound fields, which means that the energy of a specific tone is spread over a wider range of frequencies.

The study shows that at a strong push (during the cruise), the lower fan suction allows the limits flow of the cell of the cell to remain largely not disturbed. In this diet, the flow ingestion is governed by the discharge distortion induced by the curvature of the cell, which only exposes the blade tips to turbulent flow structures with low tenal.

Since the acoustic contribution of the conduit dominates to a low push, the primary noise generation mechanism is the interaction between the turbulent flow and the internal acoustic field of the duct – resulting from the “bag of hay of the duct”.

High -push (during takeoff), a strong suction of the fans disrupts the cell boundary layer Slow, producing a discharge distortion induced by the fan which attracts turbulent flow structures in Haut-de là, very little worn through a larger part of the blade beach.

This intense interaction between the deformed flow induces by the fan and the rotary blades leads to a “bag of hay of the fan”, where the unstable flow is decided several times by the rotary blades by a large part of the rotary beach.

The main researcher, Dr. Feroz Ahmed, who was based at the Faculty of Science and Engineers in Bristol, when carrying out this study, said: “These two hidden sound signatures – Haystacking – make the integrated future plane engines Feel perceptually irritating, not just loud.

“By connecting the turbulent flow ingestion models on how people perceive noise, we give engineers the tools to design future planes that seem really silent they seem.”

These ideas offer a new roadmap to design integrated engines that seem quieter, not only to measure quieter – an essential step in improving the acceptance of the public of future urban air mobility planes.

Using a high fidelity blower configuration which reproduces the conditions of the real world, the researchers have gathered detailed flow and noise data through flight regimes using advanced instrumentation, including hot wire anemometry, pressure sensors and distant microphones. This allowed them to isolate and connect each noise signature (hay back) both to its aerodynamic cause and its impact on human perception.

The implications of this research are varied.

These ideas provide usable design advice for large -scale transport aircraft, such as the Airbus Zeroe, Onera Nova, NASA / MIT Aurora D8, Airbus Nautilus and Mitsax -40 – and for new generation (UAM). Flightpath 2050 Reduction of aircraft noise of aircraft by 65%.

These results could help to design perceptually quieter engines for future electric aircraft and air taxis.

The team now plans to develop aerodynamic and acoustic control strategies to reduce both the hay homes in fans and conduits. They also seek to extend this analysis to other propulsion concepts involving turbulent flow ingestion, in order to shape the future of quiet aviation.