Exhaust silencer acoustic validation project for ACUSVIB

The present project consists of simulating the fluid-dynamic and acoustic behaviour of an engine exhaust silencer to support the manufacturer’s design calculations. ACUSVIB provides the dimensional and operating data of the equipment and DPO FLUID is responsible for transferring this data to the virtual work environment.

To visually verify in an agile way that the geometry corresponds with the real design, the first task is to perform a 3D rendering of the model.

ACUSVIB performed its own design calculations to obtain the required attenuation of its silencer, conducting acoustic measurement tests in the field once the equipment was built and installed. DPO FLUID carried out a model using finite elements in order to find the fluid-dynamic evolution and the attenuation value of the silencer frequently up to 4000 Hz.

From the fluid-dynamic simulations it is verified that the pressure drop values ​​are admissible for the installation of the equipment. The velocity profile shows that the pass of fluid along the silencer is well simulated, confirming that the flow pattern is correct.

From the comparison of the attenuation values ​​calculated by DPO FLUID with those calculated by ACUSVIB, it can be seen that there is great agreement, both in orders of magnitude and in trend. The first attenuation peak calculated by ACUSVIB occurs in a third of an octave somewhat higher than that calculated by DPO FLUID. The rest of the frequencies show similar peak values, although finite element simulations predict a peak that traditional calculations do not take into account.

After calculating the muffler output noise level, considering attenuation and ambient background noise, it is observed that both the results predicted by DPO FLUID and those predicted by ACUSVIB accurately reflect the experimental field measurements. However, in general terms, it can be concluded that the finite element calculation performed by DPO FLUID shows more precision than traditional calculations.

The completion of this validation project confirms the capabilities of the CFD / FEM in acoustics, enabling future collaborations between DPO FLUID and ACUSVIB.