Evaluation of environmental noise pollution in Mosul

Abstract The study of the internal component geometries (i.e. perforated elements) is relevant for the acoustic performance optimisation of a silencer. During the design phase, the evaluation of the properties of a silencer is performed by numerical analysis. In the literature, there is a lack of general guidelines and comparisons among different modelling strategies. So, in this study, the influence of grid type (i.e. trimmed vs tetrahedral) on the numerical prediction of the flow inside a reactive silencer is analysed. Moreover, using a porous baffle interface to model the perforated pipe is investigated, searching for a faster and easier way to model perforated elements. The simulations are carried out with the commercial CFD software STAR-CCM+. The comparison of the obtained axial velocity with a literature case study assesses the numerical model reliability. The analysis highlights that velocity and pressure predicted with both the mesh typologies does not significantly differ, but the trimmed mesh allows to save cells number, reducing the computational cost. Instead, obtain a reliable flow description using the porous baffle interface is strictly correlated to the settings of the resistance coefficient. This assumption does not provide accurate results for the analysed perforated pipe. On the other hand, using a simplified model allows to easily perform a comparison between different muffler geometries, as the holes have not to be drowned and meshed after each modification. 

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Numerical study on the influence of porous baffle interface and mesh typology on the silencer flow analysis

Nowadays the automobile industry is largely driven by designs that complies with the laws and regulations governed by environment concerns. For instance, to counter noise pollution designer came up with the idea of muffler that considerably reduces the noise produced by the engine. An effort has been made to try and compare different models of a reactive muffler through case studies after cumulatively incorporating various changes that are generally considered beneficial. This paper compares the stock muffler with new designs by considering transmission loss as the deciding factor since it is a property of the geometry alone. The more the transmission loss the better the muffler is at attenuating the noise generated by the engine. However, another important factor that should be considered when designing a muffler is the Backpressure it creates on the engine as backpressure negatively impacts its performance. The design with the highest transmission loss along with a controlled backpressure is declared as the most effective design.

Manu Sivan

Papers

CFD case studies on the acoustic performance and backpressure changes on modified reactive mufflers