Spiral Helmholtz Resonance Muffler And Absorber Design And Acoustic Characteristics Research

With the development of modern science and technology,all kinds of equipment are developing towards high-speed,large-scale,light-weight,heavy-duty and extreme environments operation,while equipment operation will have negative effects,such as noise and other problems.Low-frequency noise is an important part of environmental pollution due to its strong penetration in the process of transmission.Traditional Helmholtz resonators have some disadvantages such as selective absorption and narrow absorption band.In this thesis,a Helmholtz resonator is designed by adding spiral structure into the cavity of traditional Helmholtz resonator;according to the periodicity research,the spiral composite muffler is designed.Asymmetric absorbers were constructed based on the acoustic“soft” boundary theory,and the acoustic properties of the above structures were studied as follows:First,based on the Helmholtz resonator theory,the transmission loss is calculated for the traditional Helmholtz resonator and the helical Helmholtz resonator.Simulation results shows that the Helmholtz spiral resonators can effectively increase the transmission loss peak value by at least 7d B at the same size,and can effectively improve the transmission loss performance of the resonators.According to the geometric parameters of Helmholtz structure(inner diameter,isometric pitch and variable pitch),the Helmholtz resonator was optimized.When the inner diameter was 14 mm,the variable pitch structure with the first turn pitch of45 mm had the best effect,and its transmission loss peak reached 67.3d B at 290 Hz,which was verified by experiments.Secondly,according to the research on the periodic arrangement of resonators,a single spiral Helmholtz resonator is periodically arranged in the axial and radial directions of the acoustic pipeline,and its transmission loss is calculated.The simulation results show that the axial periodic placement of the resonator can improve the transmission loss peak and broaden the high-frequency absorption band;radially periodic placement of the resonator can effectively broaden the absorption band on both sides of the transmission loss peak.When the resonators of different sizes are connected in parallel,placing resonators with similar resonant frequencies on the acoustic pipe can effectively broaden the working frequency band of the whole structure and increase the transmission loss.Based on the periodicity regular of the resonator,the design of spiral composite muffler can achieve effective absorption in the range of 200Hz?700Hz,and the transmission loss value is higher than 20 d B.The experimental test results are basically consistent with the simulation results,and active noise control can be achieved.Finally,based on the acoustic boundary theory,a simulation model of absorption system with both ends open is constructed to calculate its acoustic performance.The result shows that the absorption coefficient of acoustic wave entering the system from one side is 94.3%;the reflection coefficient of the system entering from the other side is 97.3%,and the absorption coefficient is only 8.2%.There are two different absorption effects occur due to asymmetric structures that create acoustic “soft” boundaries.In order to broaden the application prospect of dual-port absorption system,a system with multi-band and broadband absorption capacity is designed based on the single band system.The simulation results show that the multi-frequency absorption system can have multiple absorption peaks,and the absorption coefficients are greater than 90%.The broadband absorption system can effectively absorb in the range of 240Hz?330Hz,and the average absorption coefficient reaches 54%,which has been verified by experiments.The dual-port asymmetric absorption system has good air flow exchange function while absorbing sound energy,which can be widely used in the field of noise control.