Acoustic Characteristic Simulation And Study Of Exhaust Muffler Based On CFD

With the rapid development of automobile industry, the noise pollution problem has become even more serious. The engine exhaust noise is the main noise source of automobile, it is the most direct control of noise to install an exhaust muffler. With the help of the techniques of computational fluid dynamics (CFD), acoustics and computational simulation, we research on the accoustic performance of the muffler, it has very important theoretical and practical value for improving performance of the muffler.The pulse method is one of the main methods of measuring the transmission loss of muffler, in this paper, the pulse method has been combined with CFD method, using Fluent software simulate the muffler. A single period sinusoid of suitable amplitude and duration imposed at the inlet boundary. The time history of the acoustic pressure is recorded at two points, one in the inlet pipe and the other in the outlet pipe. These time histories are Fourier transformed and the transmission loss of the muffler is calculated.Firstly, in order to introduce the method and steps of calculating transmission loss by Fluent, an simple expansion chamber muffler is as an example. By contrasting other methods, its application scope and characteristics are given:when the noise frequency is less than2000Hz, it consistents with the experimental results. And at high frequencies, changes are basically the same, but the precision of simulation results are low. The CFD method is better than the transfer matrix method in accuracy, but not as good as the boundary element method. It is also study the problem that the selection of time step and the mesh size has influence on the simulation precision.Then, the paper studies the transmission loss of the simple expansion chamber muffler changes with frequency under different structural parameters. Study on the influence of connecting pipe length, cross-sectional area and administrative area on the transmission loss of Helmholtz muffler. Study on hole diameter, perforated pipe diameter, diameter of resonant cavity of straight-flow perforated tuber muffler transmission loss of influence. The results are consistent with the theoretical analysis, the ability and characteristics of CFD method are further verified.Finally, CFD method is applied for the transmission loss of the combined type muffler, the paper researches on the relationship between transmission loss and noise frequency of two kinds of combination muffler, and the conclusions can be improved to guid the work of the muffler.