Research On The Noise Reduction Characteristics Of Double-layer Split-flow Counter-punch Perforated Pipe Structur

With the rapid development of automobile industry,automobile has been widely used in all walks of life,bringing great convenience to industrial production and peoples daily life,but also brought a lot of negative problems.One of the most obvious problems is noise pollution.One of the main sources of automobile noise is the exhaust noise produced by the engine.Nowadays resistant muffler is used to solve the problem of exhaust noise of engine.The structure of resistant muffler is a combination of perforated tube,inner cannula,resonance cavity and other muffler components.The more muffler components are combined,the better the muffler effect is.Exhaust air flow through these muffler units will be subjected to resistance,resulting in pressure loss,which increases exhaust back pressure and reduces engine power.In addition,when the exhaust air velocity of the engine is high,the high-speed air flow produces regenerative noise inside the muffler,which makes the noise reduction effect worse.Based on this,in order to reduce the airflow velocity in the muffler,a double-layer shunt hedge perforated tube structure is proposed in this paper,and its acoustic performance is studied by theoretical calculation and numerical simulation.First of all,according to the theory of one-dimensional plane waves and acoustic students basic unit of the transfer matrix is deduced double tap hedge perforated tube structure of the whole transfer matrix,the use of Matlab and COMSOL software for calculation,the transmission loss according to the transmission loss curve shows the double tap hedge acoustic properties of perforated tube structure,lay a theoretical foundation for follow-up study.And based on the overall transfer matrix,the perforated pipe,perforated tube thickness,the total length of the first layer of the perforated tube diameter and perforation rate,the second layer of perforated pipe diameter,and the influence law of perforation rate to the whole transfer matrix,the results show that the structure parameters is a key parameter to determine the transmission loss of the whole structure of,only choose reasonable structural parameters can ensure good silencing effect.Secondly,the fluid dynamics software Fluent is used to simulate and analyze the flow field inside the double-layer shunt hedge perforated pipe structure.When the inlet flow rate increases from 15m/s to 35m/s,the internal flow field of the double-layer shunt hedge perforated pipe structure is studied.The results show that the air flow through the double-layer perforated tube has obvious hedging phenomenon on the counter surface of the perforated tube cavity,and the flow velocity decreases by up to 70% when the air flow is hedging on the counter surface.It can be seen that the double-layer shunt hedge perforated pipe structure can effectively reduce the flow velocity and exhaust back pressure while ensuring the noise reduction effect.Finally,according to the two-load method,the transfer loss measurement test bench is built to measure the transfer loss data of the manufactured samples.The measurement results are compared with the theoretical calculation results,and the comparison results show that the double-layer shunt hedge perforated tube structure has better noise attenuation effect in the medium frequency range.