Design And Performance Study Of Perforated Resonators With Small Aspect Ratio

In order to efficiently attenuate the broadband exhaust noise generated by the turbocharger compressor,it is necessary to have an exhaust muffler suitable for the port with a large flow section,a small aspect ratio,and a broadband attribute.Based on this feature,this thesis conducted a research on the acoustic performance of perforated resonator with a small aspect ratio and the influence of flow on the acoustic performance of the resonator.The main contents include:1.Simulate the transfer impedance perforate in the perforated resonator,calculate the acoustic impedance value of the entire perforated plate by establishing the transfer impedance model of a single perforation,and then apply the transfer impedance simulation model to the acoustics of the muffler in the performance simulation system,the calculation results of the transmission loss within 100-3500 Hz are in good agreement with the test,which verifies the accuracy of the simulation model of the transfer impedance perforate.2.The finite element method is used to investigate the phenomenon caused by multi-dimensional sound wave propagation in the chamber of the perforated resonator.The results show that for single-chamber perforated resonator,the ratio of the chamber length l_m to the chamber radius R is 0.3,the transmission loss curve has only one resonant absorption peak in the calculated frequency range.When the length of the chamber is longer(l_m/R=3),due to the influence of non-planar waves,there are other absorption peaks on the transmission loss curve beyond the resonance frequency.In addition,through orthogonal experiments,it is found that the variation of chamber length has the greatest impact on the transmission loss of the multi-chamber perforated resonator.As the length of the chamber increases,the transmission loss enhance.3.In order to efficiently attenuate the exhaust noise of a certain type of turbocharger compressor,a multi-chamber perforated resonator model was designed,and the finite element method was used to predict its transmission loss.The structural parameters of the multi-chamber perforated resonator are optimized with the transmission loss as the optimization objective.The amplitude of the transmission loss of the optimization curve in the target frequency band is all above 3d B.Then the acoustic performance test of the resonator prototype was carried out in a semi-anechoic room,in the frequency range of 2000-2800Hz,the average values of the transmission loss test and simulation results were 5.11d B and 4.56d B.Respectively,and the test results matched the simulation results relatively well.It illustrated that it is effective to optimize the structural parameters of the multi-chamber perforated resonator by means of parameterized scanning design variables,and the designed multi-chamber perforated resonator can effectively attenuate the broadband exhaust noise of the compressor.4.Establish a three-dimensional frequency domain calculation model of single-chamber perforated resonator including grazing flow,and study the effect of grazing flow Mach number on the acoustic performance of the resonator.The results show that the peak value of the transmission loss of the resonator declines under the action of grazing flow.When the Mach numbers are 0,0.05,and 0.1,the maximum value of the transmission loss of the resonator is 32.12d B,28.46 d B,23.70d B,and the maximum value decreases about 8.42d B.At the same time,the resonance frequency of the chamber shift to high value,gradually enhancing from 1680Hz when there is no flow to 1720Hz(Ma=0.05)and 1930Hz(Ma=0.1).This is owing to the acoustic impedance of the perforated increases with the grazing flow Mach number,which leads to the reduction of the transmission loss.Meanwhile,the sound pressure level at the outlet of the resonator increases greatly with the increase of the grazing flow velocity.The sound attenuation performance of the resonator is suppressed,resulting in a reduction in the peak value of the transmission loss.In addition,the effect of mean flow greatly weakens the interaction between the main duct and the chamber,causing the peak transmission loss to gradually decrease as the resonance frequency enhances.The small aspect ratio perforated resonator chamber length has a greater impact on the acoustic performance.The multi-chamber perforated resonator formed by multiple sections in series can effectively attenuate broadband noise and suited the requirements of compressor exhaust noise control.Fluid flow will restrict the acoustic performance of the perforated resonator,and the attenuation caused by flow cannot be ignored even at low Mach numbers(Ma≤0.1).