Numerical study of the Helmholtz Resonators behavior using impedance functions
Barbara Oliveira Mendes1; Gustavo Paulinelli Guimarães1
1 UFOP - Universidade Federal de Ouro Preto
doi:10.20906/CPS/COB-2015-1139
Resumo
Helmholtz Resonator (HR) consists of a device dedicated to attenuating the acoustic pressure inside cavities, rooms and other volumes. It is not rare to find this type of device in cases in which absorption material cannot be applied or in cases that the acoustic energy must be attenuated in a specific range of frequencies (narrow band). The last option is suitable to decrease the acoustic pressure in the natural frequencies (resonances) of a cavity. The proposal of the paper is to analyze the effect of HR behavior in the impedance functions of a tube. Using a cylindrical tube as the reference cavity, a sort of HR was designed and attached (one at a time) to one of its ends. The impedance functions were obtained from harmonic analysis of a Finite Element model, which was developed considering the pressure response due to an excitation at the opposite end. The numerical acoustic impedance functions of each configuration (each HR) were compared to the function of the reference tube alone (without HR). The effect of the HR behavior could be detected not only in resonance peaks (as expected) but in the whole considered frequency range. Even if the HR tuned frequency is located between two resonances (anti-node regions), the effect could be verified clearly. In this way, it was concluded that the HR behavior can be noticed in the tube; even if the HR is tuned to a frequency which pressure responses meet the lowest levels inside it. This conclusion establishes the basis of the next study stage: to construct a HR parametric model using the acoustic impedance functions of the cavity where the HR is installed.
Palavras-chave: Helmholtz Resonator; Finite Element Analysis; Acoustic Impedance