The Attenuation Performance And Experimental Research On Inserted-pipe Reactive Muffler Considering The Influence Of Air-flow And Medium Temperature

At present, making a reactive muffler installation is the most direct noise control measures to solve the traffic, industry,enterprise exhaust equipments noise. Reactive muffler with its good acoustics, dynamic performance and higher environmental tolerability, has been got a wide range of applications and research. The major problems are focused on the muffler attenuation performance with factors of air-flow and the medium temperature. The influences mainly are two aspects, one is that the existence of the air-flow can change the pipe-sound propagation and decay laws; one is the air-flow velocity state will also cause the muffler air-flow regeneration noise. When air flows through the muffler, the mutation of muffler cavity section, solid side can make air-flow produce eddy current to exacerbate the pipeline surface friction with air-flow. And the vortex unsteady air-flow produced will stimulate the muffler ontology vibration to produce noise. It will greatly bring down the effect of muffler noise attenuation, and even make muffler into a noise generator. The temperature of the medium is also a factor which influences the pipe sound, and is benchmark factor on the energy exchange of muffler. With the research on muffler considering the air, temperature and air temperature coupling factors, it will reveal the muffler air-flow regeneration noise phenomena and trigger mechanism, realize quantitative description of the air-flow regeneration noise and the forecast. These have an important realistic meaning for optimizing internal flow field of muffler and controlling the flow noise and improving attenuation performance.Main task this thesis is that using test technology to research the muffler performance:(1)According to the working condition of the reactive muffler, combined with pneumatic acoustics theory, acoustic testing national standards and muffler test technology, in this paper, it designed the muffler test-bed to fully simulate the actual working condition of the exhaust muffler which connected with the engine and power equipment. Then it used the noise collection and analysis technology, such as B&K test technology and instruments such as vortex flowmeter, pressure transmitter, to provide test software and hardware support on the research that how air-flow and temperature impact the muffler performance.(2)In this paper, it designed and implemented the muffler bench test and muffler ontology modal test. In three working conditions, it tested the muffler transmission loss, pressure loss, air-flow regeneration noise and ontology structure vibration. The main test methods are two-microphone transfer function test method, sound pressure differential method and modal test method. Through the test and data comparison, it analyzed the influence laws of muffler acoustic and aerodynamic performance with different flow speeds and medium temperature.(3)Combined with noise, vibration and modal test theory, in different flow speeds, it studied the muffler transmission loss, air-flow regeneration noise and the muffler ontology vibration in the static and dynamic conditions, and made a data contrast in the frequency domain. It told the relationship between the muffler ontology modal frequency and muffler Silencing frequency.