The aviation industry has been pressured by aviation regulatory agencies to reduce the noise levels generated by the aircraft they manufacture, so that, by 2030, it will no longer be possible to hear the noise of a plane when taking off or landing outside the airport perimeter.
One of the solutions to this problem was found by researchers from the State University of Campinas (Unicamp) in the wings of owls (Strigiformes).
When studying the aerodynamics of the bird's flight, considered the quietest, researchers from the Aeronautical Sciences Laboratory of the Faculty of Mechanical Engineering (FEM) at Unicamp, in collaboration with colleagues from the Technological Institute of Aeronautics (ITA) and Lehigh University, of the United States, identified characteristics in owl wings that, mimicked in airplane wings, make it possible to design quieter aircraft.
“We developed a mathematical numerical model to simulate some characteristics of owl wings on airplane wings and proved through experiments that this makes it possible to design quieter aircraft,” he says. William Wolf, professor at FEM-Unicamp and one of those responsible for the project on the Brazilian side.
Wolf is one of the principal researchers at Center for Research in Computational Engineering and Sciences (CCES) and associated with Center for Mathematical Sciences Applied to Industry (CeMEAI).
CCES and CeMEAI are Research, Innovation and Dissemination Centers (CEPIDs), financed by FAPESP.
According to the researcher, planes have several sources of aerodynamic noise, generated by turbulence in the air flow that passes around the wings. Turbulence generates disturbances that convert air velocity energy into acoustic waves.
During takeoff, when the aircraft needs maximum power to take off, most of the noise is generated by the engine. During landing, when engine power is reduced, the main sources of aerodynamic noise become the landing gear and the hyper-supporting surfaces, made up of the wings, flaps e slats – mobile devices located on the wings with the function of increasing the surface area and increasing the aircraft’s lift.
“Aerodynamic noise is caused by turbulence at these points on the aircraft,” explains Wolf.
In recent years, new aeronautical engines have become more efficient and larger, meaning they have had to be located closer to the aircraft's wings in order to stay away from the ground. This approach generates an interaction between the noise generated by the engine and the trailing edges – the rear part of the wings –, which causes acoustic scattering and increases the noise of new aircraft, explains Wolf.
In order to find a solution to this problem, researchers studied the morphology of owl wings to identify the characteristics that make the bird's flight silent, reducing noise.
The researchers observed that owl wings have velvety feathers, with elastic and porous fringes in both the front and back regions – the leading and trailing edges –, which break the turbulence structures into smaller portions, reducing noise. Furthermore, the trailing edge is slightly serrated, which also helps to reduce noise during flight.
“All of these elements found in the owl’s wings act to reduce the bird’s noise,” says Wolf.
Based on these findings, the researchers developed a wing system with swept back region – in which the inclination is directed towards the front of the aircraft. This change made it possible to reduce the spread of engine noise at the trailing edge, modifying acoustic diffraction and reducing noise generation.
The study, supported by FAPESP, resulted in the deposit of patents in Europe and the United States about this new silent wing design concept. The studies were carried out in partnership with researchers from ITA, the University of Poitiers, in France, and Airbus.
Noise in landing gear
Unicamp researchers have also developed projects in this area of research, called aeroacoustics, in partnership with Boeing.
In collaboration with engineers from the North American aerospace company, they evaluated, using computer simulations and statistical techniques, the effects of turbulence on the landing gear of a 777 model aircraft, manufactured by Boeing.
The analyzes indicated that the main sources of noise in this component are cavities in the aircraft's wheels and fuselage, used to store the landing gear during flight.
“We discovered that, under certain frequencies excited by turbulent flow, some of these cavities present resonance effects that generate a very intense noise that can be extremely disturbing to the human ear,” says Wolf.
To carry out the simulations, which required 7,5 million hours of computing, running the data over six consecutive months, a supercomputer in the United States was used with 3,2 processing cores in parallel.
“It was one of the largest computer simulations ever carried out by Boeing. A single simulation generated 50 terabytes of data,” says Wolf.
Matter originally published on the Fapesp Research for Innovation website.
