Abstract:
Large Eddy Simulation is a method of obtaining high accuracy computational
results for modelling fluid flow. Unfortunately it is computationally expensive
limiting it to users of large parallel machines. However, it may be that the
use of LES leads to an over-resolution of the problem because the bulk of
the computational domain could be adequately modelled using the Reynolds
averaged approach.
A study has been undertaken to assess the feasibility, both in accuracy and
computational efficiency of using a parallel computer to solve both LES and
RANS type turbulence models on the same domain for the problem flow over
a circular cylinder at Reynolds number 3 900
To do this the domain has been created and then divided into two sub-domains,
one for the LES model and one for the kappa - epsilon turbulence model. The hybrid
model has been developed specifically for a parallel computing environment
and the user is able to allocate modelling techniques to processors in a way
which enables expansion of the model to any number of processors.
Computational experimentation has shown that the combination of the Smagorinsky
model can be used to capture the vortex shedding from the cylinder and
the information successfully passed to the kappa - epsilon model for the dissipation of the
vortices further downstream. The results have been compared to high accuracy
LES results and with both kappa - epsilon and Smagorinsky LES computations on the
same domain. The hybrid models developed compare well with the Smagorinsky
model capturing the vortex shedding with the correct periodicity.
Suggestions for future work have been made to develop this idea further, and
to investigate the possibility of using the technology for the modelling of mixing
and fast chemical reactions based on the more accurate prediction of the
turbulence levels in the LES sub-domain.
