Simulation Of Turbulence Noise And Optimization Design For Marine Diesel Engine Muffler

As the simplest and effective noise reduction equipment in intake and exhaust system,the muffler is widely used in the shipbuilding industry.However,with the increase of engine power and the increase of airflow velocity in the intake and exhaust system,the regeneration noise of muffler becomes a problem that can not be neglected.The generation factors of muffler regeneration noise are complex,among which the turbulence noise generated by the fluid flow instability caused by the complex structure of the fluid inside the muffler is the main component.In this paper,the turbulence noise of muffler is studied.In this paper,the RNG model in Fluent is used to analyze the flow field of six basic silencing structures.Moreover,the internal-field turbulent noise is analyzed by the broadband noise model.According to the results of numerical calculation,the generation mechanism of turbulence noise in the acoustical structure is obtained,that is,the velocity gradient caused by the silencing structures is the reason that induces turbulent noise.Besides,the main areas inducing turbulence noise of six basic silencing structures are summarized,which are the wall of inlet and outlet pipe,the outer flame area of velocity potential core and the wall of each silencing structure.Considering the outlet offset silencing structure and outlet intubation silencing structure as the objects,the spectrum characteristics of turbulent noise in the external field are studied by using the hybrid method of Fluent and Virtual.Lab.By analyzing the frequency response curve of sound pressure level of the turbulent noise,the influence of the outlet offset distance of the long expansion chamber,the outlet offset distance of the short expansion chamber,the offset distance of the outlet cannula and the length of the outlet cannula on the turbulent noise of the airflow are obtained.And the internal flow field of each research object is analyzed to obtain the reasons for these influence rules.The optimization design of marine diesel engine intake muffler is carried out,and predicted and analyzed by numerical calculation.The numerical results show that the performance of the optimized muffler is improved.Referencing the experimental data of the resistance and acoustical performance of the optimized muffler,the accuracy of the numerical calculation is verified.The experimental results show that the resistance performance and acoustical performance of the optimized muffler have been greatly improved.With the 110% working conditions of the diesel engine,the resistance of the muffler decreases by 100 Pa,and the insertion loss in the frequency range of 2000Hz-5000 Hz increases by about 15 d B.