Study On Subsonic Jet Noise Reduction By Using Porous Structures

Jet noise exists widely in industrial procedure and people's daily life.One of the most important concerns is the noise generated by the jet aircraft engine which may make a great influence on the environment and the comfort of passenger.Controlling of jet noise mainly aims to damage the formation and development of large scale coherent vortices.There are two main methods,i.e.,active and passive methods.Since the passive methods have no need of additional equipment,and it is easy to realize,so they are widely preferred by researchers.Porous wall treatments can effectively affect the flows near the wall,and don't change the geometry of the object.The application of using porous treatments to control jet noise has not been found in the literature.In this paper,a subsonic jet flow is studied by experimental analysis and numerical simulation.On the basis of measurement results,a variety of extensions with multiple blind holes and porous plate cavity structures are designed.Their noise reduction effects and theory are analyzed.A subsonic jet test rig was set-up at the beginning of the study.By ensuring the operation parameters to meet the design requirements,the distribution of the sound field of the subsonic jet was measured and the influence of the jet Mach number on the noise was obtained.The changes of sound field under different porous structures are measured.It is found that porous structure can improve the condition of sound field in reducing the noise in the frequency range of 3000?8000Hz.The Large eddy simulation method is used to study the compressible jet flow of Mach number Ma=0.5.In order to compare the influence of porous cavity structure on the jet flow,the flow field under different parameters of porous cavity nozzle is calculated respectively.The jet shear layer instability and other turbulent parameters are analyzed.The result shows that porous cavity structure effectively destroys the jet exit ring vortex structure,which effectively affect the formation of large scale vortex and reduces its related sound sources.The structure designed in this paper produce obvious effect on subsonic jet noise acoustic spectrum with various characteristics.The results provide a new way for jet noise passive control technology,and provide a basis for the further research and development of related structure.