Aeroacoustics modelling using large-eddysimulation
Problem description
Flow-induced noise around a model wing mirror of
a road vehicle.
Physics and modelling
Incompressible transient large-eddy simulation of
a flow behind a model wing mirror. The simplified wing mirror geometry
is assembled from a half-cylinder capped by a quarter sphere and
attached to a flat wall. The objective of the simulation is to predict the
surface pressure oscillations and flow induced noise sources in the flow
field. Propagation of noise into the far field is not modelled; instead,
the noise signature is assembled from the local pressure variation. A
consequence of this approach is that the acoustic spectrum that can be
resolved is dependent on the mesh resolution (this can be extended to
higher frequencies by sub-grid scale modelling). A variety of different
sub-grid scale LES models has been used. The simulations presented
below have been made using the 1-equation model. The plots represent
the results of a simulation with 700,000 cells - a very coarse mesh. The
original geometry was developed by Drs. Raimund Siegert and Volker
Schwarz working for DaimlerChrysler AG.
OpenFOAM solver
oodles, a Large-Eddy Simulation code from the OpenFOAM
library.
Images and animations
Instantaneous vortex cores, represented by iso-surfaces of the
second invariant of the velocity gradient tensor larger than zero.
The formation and shedding of role-up vortices on the mirrors
front surface can be clearly seen.
The mean square of the fluctuating pressure component on the
mirror and wall surfaces. The regions of high pressure fluctuation
intensity behind the mirror trailing edge near the wall are clearly
shown.
The mean static pressure on the wing mirror’s front surface. Note
the band of higher pressure near the mirror’s trailing edge, caused
by incipient separation in this region.
The mean surface shear stress on the mirror and surrounding
wall. Note the regions of high surface shear at the junction of
the mirror’s trailing edge and the wall. These regions are a major
source of the turbulent pressure fluctuations. Other noteworthy
features are the recirculating zone behind the mirror delineated
by zero wall shear stress, and a band of lower surface shear near
the mirror’s trailing edge caused by incipient separation in this
region.
Author
The work on this project has been performed by Eugene de Villiers, a
postgraduate student at Imperial College, London. The geometry
and sponsorship is provided by DaimlerChrysler AG and gratefully
acknowledged.
