| Reducing the noise emission is an important direction of technological progress of construction machinery products.As an important component of an engine exhaust system,the mufflers directly affect the noise level of the construction machinery.The diesel engine muffler matched with the construction machinery usually has a multi chamber complex structure formed by the combination of multiple resistant muffler units.At present,there are some problems in multi chamber resistant muffler for construction machinery,such as complex variation law of transmission loss(TL)curve with frequency,which is not superposition of the TL of each chamber in high frequency band,mutual effect of flow field performance between chambers,and unclear relationship between turbulent kinetic energy parameters and airflow noise characteristics,which hinder the improvement of noise emission level of construction machinery products.Therefore,the research on the acoustic,flow field and airflow regeneration noise characteristics of multi chamber resistant muffler has theoretical research significance and engineering value for shortening the design and analysis cycle,effectively guiding the engineering practice process and reducing noise emission.Taking the typical two chamber mufflers as the research carriers,this paper establishes the coupling mathematical model between chambers,deeply analyzes the influence law of structural parameters on the coupling effects of acoustic performance.and reveals the coupling mechanism;Taking the parameters of pressure loss,velocity and turbulent kinetic energy as evaluation indexes,the interaction law of flow field characteristics between muffler chambers is studied,and the "impedance boundary conditions" of flow field in different chambers are summarized,which can intuitively reveal the coupling mechanism of the flow field characteristics of chambers;Through the derivation of the acoustic analogy equation,a sound source relationship model of turbulence kinetic energy parameters and flow noise suitable for muffler is established,which provides a basis for improving the flow noise characteristics of muffler by the optimizing methods of turbulence kinetic energy,and lays the foundation for improving the performance of multi-chamber resistance muffler.The main research progress is as follows.Firstly,the mathematical model of coupling effects between muffler chambers is established according to the multi-order modal amplitude coefficients of incident and reflected acoustic waves at both ends of the connecting pipe.The acoustic coupling effects of muffler units such as two expansion chambers,two resonant chambers and resonant expansion chambers are solved by the two-dimensional axisymmetric analytical method.The influence of different structural parameters on the acoustic coupling effects of the chambers are analyzed.It is concluded that the acoustics performance of muffler depends on the second chamber,and the attenuation performance of the first chamber is weakened by the coupling effects,and that of the second chamber is enhanced.Based on the acoustic impedance transfer theory,the mathematical relationship between the equivalent impedance of the two chambers is obtained,and the chamber coupling mechanism is revealed,which can provide a theoretical basis for the further study of the masking effect between muffler units.Secondly,employing acoustic finite element method and orthogonal test method,and taking the matched resistant muffler of a certain excavator as the research carrier,the influence law of each muffler unit on attenuation performance is redefined and analyzed,and the conclusions about the masking effect between the muffler units are obtained.According to the research conclusions,the acoustic performance improvement of the corresponding muffler is completed,which is verified by the installation test,achieves the expected results,and verifies the effectiveness of the research conclusion of the acoustic performance and masking effect of the muffler elements.Thirdly,based on the research conclusion on the coupling effect of acoustic characteristics between the chambers,the flow field characteristics of two chamber mufflers are studied.By optimizing the calculation parameters of local pressure loss,a pressure loss prediction model of multi-chamber muffler is proposed;The flow field characteristics of the second chamber are compared to the acoustic impedance boundary conditions,and the influence of structural parameters on the coupling effects of the flow field characteristics between two chambers are analyzed.Aiming at the lack of flow field performance of conventional perforated pipe,the riblet bionic structure is introduced,the drag reduction effects of the perforated pipe with riblets are studied,and the flow field performance of muffler is improved.Fourthly,based on the research conclusion of turbulent kinetic energy parameters of muffler,utilizing turbulence governing equations and guided by the idea of acoustic analogy,the mathematical relationship between turbulent kinetic energy and flow noise suitable for resistant muffler is gradually deduced;According to the drag reduction characteristics of riblet structures,the internal field treatment method of sharp wall vortex is introduced,and the steady vortex acoustic equation is obtained,which explains the phenomenon and the conclusion that there is no propagatable flow noise near the wall of riblet structures.Finally,the design and optimization processes of the complex-structured resistant muffler for construction machinery are put forward based on the research conclusion of multiple evaluation indexes.Taking the resistant muffler used in a bulldozer as the application object,comparative analysis are carried out by means of numerical analysis,bench test and real vehicle test,which prove that the improved muffler can significantly reduce the exhaust noise on the premise of keeping the pressure loss essentially unchanged.With other comprehensive measures,the exterior emission sound power level and the emission sound pressure level at operator's position have been greatly improved. |
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