Research Of Pipe Orifice Acoustic Reflection Characteristics And It's Application On Muffler

Muffler is one of the important components in the exhaust system,which can directly affect the exhaust system of the vehicle and noise outside the vehicle.Therefore,the muffler has been a hotspot.As an important factor affecting the performance of the exhaust muffler,the optimization and improvement of the muffler has important value for improving the overall performance of the muffler.The article summarizes the development of mufflers.At present,the research on mufflers is generally concentrated on the optimization and improvement of the internal structure,while the effect of the outlet on the performance of the muffler has not yet been fully recognized.There is a reflection when the sound propagates through the pipe to the nozzle,which shows that the sound waves will not totally radiate out of the pipe at the nozzle,and there will be a certain amount of sound waves reflect back into the pipe.In this paper,the acoustic reflection characteristics of the nozzle are applied to the muffler to improve the noise reduction performance.Firstly,the regularity of the reflection on the acoustic wave at the nozzle is summarized.The design is performed using standing wave tube to observe the reflection coefficient.On the basis of summarizing the acoustic reflection characteristics of the nozzle,the acoustic impedance ratio of the nozzle is calculated to replace the air characteristic impedance as the boundary condition of the outlet and substituted into Virtual.Lab for acoustic finite element calculation to improve the calculation result.Relevant experiments have proved that the calculation results on improving the outlet boundary can represent the acoustic reflection at the nozzle,which is more in line with the actual situation.The study on the influence of the nozzle parameters on the acoustic reflection,takes the acoustic reflection characteristics of the nozzle as a guide and is based on the calculation of improved export boundary.From the theoretical analysis of the acoustic reflection characteristics,there is a correlation between the reflection coefficient and the diameter of the pipe.The reflection coefficient increases when the diameter decreases.Therefore,it is raised that the number of nozzles affects acoustic reflections,and the conclusion has been reached that the same flow area is maintained,the use of multiple outlet tubes to reduce the diameter of the tubes,and the sound attenuation performance could be improved.Corresponding experiments have been conducted to verify the result.In addition,changes on the length of the outlet pipe will also affect the performance of the muffler,and an appropriate length of pipe should be selected for the specific noise source.According to the phenomenon that the large number of sound waves appear locally when the tube length is equal,the research on the performance of the double outlet tube with different tube lengths is proposed with the analysis of the impedance characteristics.Compared with equal length outlet tubes,impedance matching of outlet tubes of different tube lengths changes and local frequency domain reflectance increases.Based on mastering the pipe characteristics,the research results have been applied to the muffler to examine the influence on the outlet pipe.For the influence of the number of pipes,the analysis result on the muffler shows that the double outlet pipe muffler performs better than the single outlet pipe muffler when the cross-sectional area is the same,and the triple outlet pipe muffler performs better than the double outlet pipe muffler,which is consistent with the conclusion of the study at the export side.On the basis of the influence of the length of the outlet pipe on the performance of the muffler,we continue to study the change of the double outlet muffler with unequal intubation length,which has the effect of improving the noise reduction;Considering the traditional aesthetics,it is necessary to have the same length at the outlet end,and it is proposed to arrange the structures with different lengths of the two tubes inside the muffler.Research shows that this structure can also improve the noise reduction in the local frequency domain.In short,the acoustic reflection characteristics of the muffler nozzle need to be considered.It is more reasonable to use the acoustic impedance of the nozzle as the boundary conditions for the outlet.In addition,the export side of the muffler has several certain characteristics.Grasping these characteristics and properly controlling the parameters of the export side has a certain effect on the improvement of muffler performance.