Noise-canceling structures are an integral element of modern aircraft engines. They represent a honeycomb structure made of polymer composites, which absorb acoustic waves due to resonant interaction. The requirements of the International Civil Aviation Organization (ICAO) to the level of sound absorption of such structures are gradually tightening. To keep the domestic aircraft industry in step with the times, Perm Polytechnic has designed an “intelligent” noise-canceling structure with effective sound absorption in a wide range of frequencies.
To reduce noise in the front hemisphere of the engine, sound-absorbing structures in the form of honeycomb panels of resonant cells are placed on the inner surface of the air intake, and to reduce noise in the rear hemisphere – on the walls of the outer air duct. The design of such structures is based on calculations of the ability of the system to counteract sound waves in the channels of the aircraft engine.
Researchers at Perm Polytechnic Institute modeled the operation of a single noise-canceling cell and a group of such cells, taking into account parameters that were not previously taken into account. They performed computational experiments, varying the perforation diameter in the cells, and determined the scheme of their mutual arrangement for the best noise attenuation.
“To implement the identified patterns, we developed a model for adaptively controlling the resonant frequencies of the cells through piezoactive elements embedded in the perforations, which can convert mechanical stress to electrical charge and vice versa. Thus, the piezoactive elements transform the electric voltage applied to them into the deformations that change the diameter of the necks of the adaptive resonators,” said the project manager, acting head of the department of mechanics of composite materials and structures at Perm Polytechnic University, leading researcher of the research laboratory of the spatially reinforced composite materials, candidate of technical sciences Pavel Pisarev.
According to his words the revealed combinations of the perforation diameters and the schemes of the mutual arrangement of the elements can be applied for the design of the noise absorbing constructions including the adaptive ones.
Reliability of the results obtained by means of mathematical modeling is confirmed by their comparison with experimental data. The design demonstrates effective sound absorption in a wide range of frequencies with a minimum increase in its weight, which is extremely important for aircraft construction.
The conducted research will make it possible to improve the noise reduction technology in aircraft engines. In addition, the identified laws of oscillatory processes in acoustic resonators are also relevant to other areas of application, in particular, for the design of some types of combustion chambers.
