CFD Analysis of the Acoustic and Mean Flow Performance of Simple Expansion Chamber Mufflers

Abstract

The acoustic and mean flow performance of different configurations of simple expansion chamber mufflers has been considered. The different configurations include extended inlet/outlet pipes and baffles inside the expansion section of the muffler. Both the acoustic and mean flow performance has been evaluated for each muffler. The acoustic CFD model of the muffler uses an axisymmetric grid with no mean flow and a single period sinusoid of suitable amplitude and duration imposed at the inlet boundary. The time history of the acoustic pressure and particle velocity are 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. The mean flow model of the muffler uses the same geometry, but has a finer mesh and has a suitable inlet velocity applied at the inlet boundary and the pressure drop across the muffler is found. The acoustic performance is compared with published experimental results.

Sound attenuation analysis of water-filled perforated pipe silencers using three-dimensional time-domain computational fluid dynamics approach

“…Middelberg et al 4 proposed the two-dimensional (2D) axisymmetric CFD approach to calculate the acoustic characteristics of expansion chambers, and their predictions agree well with the published experimental data. Based on the impulse test technique, Broatch et al 5 applied the 3D time-domain CFD approach to predict the transmission loss of a simple expansion chamber and a reversing chamber muffler, and the predictions match fairly well with the experiment measurements and FEM results for the case without air flow.…”

Large Eddy Simulation of acoustic pulse propagation and turbulent flow interaction in expansion mufflers

“…In the present work, a pressure-based hybrid algorithm, derived from the PISO solver developed by Issa [4] and the low Mach number flow solver developed by Karki [18], is presented and applied to a low Mach aero-acoustic expansion muffler. There has been similar work reported in the recent past to simulate acoustic pulse propagation through expansion chamber using commercial CFD codes [19,20]. However, the solvers employed were found to be computationally stiff and lead to divergence of solutions when a fluctuating random signal was introduced inside the computational domain.…”

“…A pure single period sinusoid, with a time period of 0.3125µs, equivalent to a 3200 Hz frequency and amplitude of 0.05 m/s was superimposed upon a zero mean velocity at the inlet of the expansion muffler. The computational domain was defined to include an extended inlet and outlet, fourteen times the length of the expansion section, as recommended by [19]. This was adopted to ensure an appropriate wave propagation time would be possible, such that a sufficient amount of data to obtain reasonable results could be obtained (see Figure 1).…”

Predictions and experimental studies of the tail pipe noise of an automotive muffler using a one dimensional CFD model

“…In the work by Ji et al [5][6][7], the BEM predictions obtained three-dimensional analytical results for several silencer configurations which are in good agreement with experiments. In the work by Middelberg et al [8], 3D CFD was successfully used to evaluate both the mean flow and acoustic performance of an expansion chamber muffler, with various modifications including baffles and extended inlet/outlet pipes.…”