Numerical Simulation And Characteristics Analysis Of Flow Excited Noise In Mufflers

The muffler is widely used to reduce the noise propagation in the pipeline.However,as the airflow velocity in the pipe increases,the problems of airflow regenerative noise and flow-excited structure radiated noise become more serious,which affects directly the noise attenuation performance of the muffler,and may even become a noise amplifier.Therefore,study on the problem of flow-excited noise in the muffler has important theoretical significance and engineering application value.This paper mainly uses CFD software ANSYS FLUENT and acoustic software MSC ACTRAN joint simulation to study the airflow regenerative noise inside muffler.The flow field model is established,and the convergence result of the flow field steady state calculation is taken as the initial state of the unsteady state calculation.After the convergence of the unsteady state calculation is determined,the flow field data of each time step is derived and converted to sound source by Lighthill analogy in MSC ACTRAN.The finite element method is used to calculate the sound propagation.The regenerative noise simulations of the expansion chamber muffler,the inserted tube muffler,the straight through-perforated tube muffler,the eccentric tube muffler and the perforated plate muffler at different flow rates were carried out.It was found that the sound pressure level of the regenerative noise is increased as the airflow velocity increasing.The flow field and sound field are analyzed,and the causes of regenerative noise are discussed.The influence of inserted length and eccentric tube distance on airflow regenerated noise is analyzed.The flow-excited structure vibration and noise radiation of the expansion chamber muffler are studied.The influences of the constraint condition and the thickness of the shell on the vibration response and the radiated sound power are analyzed.It is found that the airflow through the muffler can arouse the natural mode of the structure and form a resonance leading to amplifying the vibration amplitude near the frequency.The larger the thickness of the shell,the more the constraint,the more sparse the structural mode,the smaller the vibration response of the flow-excited structure,and the peak frequency shifts to the high frequency,the lower the acoustic radiant energy.The sound pressure level at different flow rates is measured at the Helmholtz cavity,and the velocity-frequency-sound pressure level map is plotted.The sound pressure level of the straight tube is measured at the same position to determine the frequency of whistle noise about Helmholtz resonator.It was found that there was a whistle noise between 0.8 and 0.9 in Strouhal number and analyzed the cause of whistle noise.