Sound absorption by a Helmholtz resonator

Experiment-simulation Study on Noise Reduction of Cylinder Shell with Horn Helmholtz Resonator

“…where, l * and δ * denote the effective length and neck correction of the air in the resonator neck respectively. The reflection coefficient has the form [12] H H…”

Study of the combined muffler effectiveness

“…Aerodynamic noise, in terms of its level, significantly exceeds structural noise. However, the problem of its reduction is currently being successfully solved by selecting the volume and structure of mufflers in the intake and exhaust systems, while the aerodynamic resistance of the muffler should be minimal [1][2][3][4][5][6].…”

On the influence of lateral cells and local perforation of resonance liner samples on the accuracy of determining their acoustic characteristics in experimental studies

“…As you know, in modern turbofan engines, due to the high degree of bypass, the dominant source is the fan [1,2], and the main means of reducing the fan noise are resonant liner. Liner design is based on semi-empirical models [3][4][5][6][7][8][9][10], the main disadvantages of which include: 1) simplified mathematical formulations, which do not fully take into account physical effects (compressibility, viscosity, thermal conductivity, vortex formation), which are important from the point of view of an accurate description of SAS operation processes at high sound pressure levels typical of aircraft engine channels; 2) relatively large scatter of semiempirical coefficients used in the models (for example, the attached length of the resonator throat varies from 0.785 to 0.85 of the diameter of the perforation hole in different works [11][12][13], and in the presence of a tangential flow it varies even more [14]), which noticeably affects the accuracy of the description of the liner impedance; 3) the acoustic characteristics of only 1layer liner are predicted relatively acceptable.…”