الفهرس | Only 14 pages are availabe for public view |
Abstract The present thesis introduces a study and investigation for numerical simulation of the performance of a muffler (silencer) of internal combustion engine. Muffler (silencers) are widely used in both internal combustion engines and blowers to minimize exhaust noise. In the current work, a three-dimensional (3-D) time-domain computational fluid dynamics (CFD) model is developed for modelling for the airflow in the muffler. The plane wave decomposition method are used to forecast the transmission loss of reactive silencers. The incompressible flow form of Navier–Stokes equations with the realizable k–ε turbulent flow model using enhanced wall treatment of turbulence are solved for this purpose using finite volume solver ANSYS FLUENT-19.2 commercial package. The objective of this dissertation is to enhance the transmission loss for better damping for sound pressure wave The ensuing unstable flow calculations are started with a steady flow computation that is completed using a mass-flow-inlet boundary condition. To execute the initial computation of unstable flow, an impulse (acoustic excitation) is applied over the constant mass flow at the model’s intake. Upon complete propagation of the impulse wave into the silencer, the non-reflecting boundary condition (NRBC) is included. A second unsteady flow computation is carried out for the case where there is no acoustic stimulation at the intake. The time histories of both pressure and velocity at the upstream and downstream are examined at certain locations, as well as the pressure history at the downstream measuring point, are recorded during the two transient calculations. There are differences between the two unstable flows in the associated auditory values. Consequently, the incident sound pressure signal is derived by using plane wave decomposition upstream and the transmitted sound pressure signal is only the sound pressure downstream. Following the Fast Fourier Transform (FFT) to transfer the two sound pressure signals from the time domain to the frequency domain, the transmission loss (TL) of the silencer is computed. In order to enhance the transmission loss TL of airflow inside the muffler, three different schemes are adopted and investigated. The first scheme deals with the effect of increasing the number of perforated holes in the transverse section. While the second studies the effect of increasing the number of perforated holes in the longitudinal section. The last one investigates the effect of muffler chamber profile from circular profile to elliptic profile with different aspect ratio followed by the investigation of perforated pipe orientation in this elliptic profile. In addition to improving the geometry by adding more holes to the muffler’s cross-section, the numerical calculations and the provided data correspond well with the published results. The best optimum geometric shape for the muffler chamber is analysed by changing the circular shape to an elliptic one with a different ratio. The numerical calculations and the reported data showed that the TL increases with the increase of number of holes in the cross section area and with changing chamber profile to ecliptic shape at aspect ratio of 1.2. |