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Aeroacoustics of automobile exhausts

Automobile exhaust treatment system
An automobile exhaust treatment system
This project is in partnership with Swenox AB, an automobile exhausts
manufacturer based in Sweden. Automobile exhaust pipes consist of T-junctions
that can sometimes whistle loudly because of an interaction of acoustic waves
with flow instability. It is important to suppress this annoying source of
noise to meet legal requirements.
The project would involve a combination of numerical simulations and
mathematical modelling. Swenox has a database of experimental results. We will
perturb the time-averaged flow field and see if the perturbations are stable
or unstable. This can be achieved by simple numerical simulations. When
unstable modes are reinforced by acoustic resonance modes of the duct, a loud
tonal noise is produced. The aim of the project is to develop a physics based
model to explain this mechanism. The model could provide useful guidance for designing
quiet automobile exhausts.
Relevant IIB modules: 4A15, Aeroacoustics (Michaelmas 2012) and 4A10, Flow instability (Lent 2013)
Kelvin-Helmholtz instability in a T-junction
Kelvin-Helmholtz instability in a T-junction