Investigation On The Acoustic And Aerodynamic Characteristics Of One Innovative Vortex-shaped Muffler Unit

Noise pollution is one of the four main pollution sources in the world,which could affect both physical and psychological health.With the increase of vehicle ownership in global,the exhaust noise of vehicles has become a main source of noise in the environment.How to design a muffler with a simple geometric structure and good acoustic performance in a limited installation space to attenuate exhaust noise has become an urgent issue for researchers and technicians.The reactive muffler attenuates the energy of the sound wave by abrupt changes in the internal section or by connecting with the resonance cavity,which is characterized by its simple geometric structure and low cost,is widely used in exhaust system of vehicles.Based on the structural characteristics of one novel vortex-shaped tube,the vortex-shaped muffler unit is purposed for the first time by forming vortex structure on smooth surface of the reactive muffler unit,its acoustic characteristics and aerodynamic characteristics are studied by using the numerical simulation.Firstly,the comparison with the smooth muffler unit proves that the vortex structure has the effect of enhancing noise reduction.The acoustic performance and related mechanism are further studied.Results show the vortex-shaped muffler unit effectively increases the upper limit cut-off frequency and enhances the peak of the transmission loss at high frequency.On this basis,the variation of structural parameters on the acoustic characteristics of the vortex-shaped muffler unit is systematically analyzed.For the vortex-shaped muffler unit composed of vortex-shaped expansion chamber and smooth perforated tube,the influence of the geometrical parameters of the vortex structure,the inter-section angle of vortex,the spacing of vortex,the depth of vortex and the width of vortex,on the acoustic performances of the vortex-shaped muffler unit are analyzed.It's found that the depth and intersection angle of vortex structure are the main factors influencing acoustic performance,a suitable range of values for each geometric parameter is obtained.The novel series connection way,which connecting different muffler units with deep vortex structure,is proposed.Comparing to the traditional series connection way,the novel series connection way improves the acoustic performance in 2000~2600Hz,reduces the value of transmission loss in 1200~1800Hz respectively,suitable for situations where high frequency noise needs to be attenuated.Finally,The ratio of pressure loss of the vortex-shaped muffler unit to the smooth muffler unit is defined as an evaluation index,The variation of the pressure loss ratio of the muffler unit with the intersection angle and depth of vortex structure at different inlet flow velocity is studied,and the corresponding geometric parameter set of the best aerodynamic performance is found,?=60°,h=24mm.The vortex structure can effectively improve the mid-high frequency noise reduction performance,reduce pressure loss and energy consumption within a certain parameter range.Vortex-shaped reactive muffler as a new type of automobile muffler,the research of this paper will provide a theoretical reference for its design and application.