A novel dynamic forcing scheme incorporating backscatter for hybrid RANS/LES
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Date
2014-07-25
Authors
Xun, Qianqiu
Journal Title
Journal ISSN
Volume Title
Publisher
AIP Publishing
Abstract
In hybrid RANS/LES, Reynolds-averaged Navier-Stokes (RANS) equations method
is used to treat the near-wall region and large-eddy simulation (LES) is applied to the
core turbulent region. Owing to the incompatibility of these two numerical modelling
approaches, an artificial (i.e., non-physical) buffer layer forms along the interface
where the model switches from RANS to LES. In this thesis, a novel dynamic forcing
scheme incorporating backscatter is proposed in order to remove the artificial
buffer layer. In contrast to previous forcing techniques, the proposed forcing is determined
dynamically from the flow field itself, and does not require any extraction of
turbulent fields from reference direct numerical simulation (DNS) or high-resolution
LES databases. The proposed forcing model has been tested on three types of wall-bounded turbulent flows, namely, turbulent flow in a plane channel; turbulent flow in
a spanwise rotating channel; and turbulent flow in a spanwise rotating rib-roughened
channel. In order to validate the present hybrid approach, turbulence statistics obtained
from hybrid RANS/LES simulations are thoroughly compared with the available
DNS results and laboratory measurement data. Based on the study of a plane
channel flow, transport equations for the resolved turbulent stresses and kinetic energy
are introduced to investigate the effects of dynamic forcing on reduction of the
thickness and impact of the artificial buffer layer. As long as the dynamic forcing is
in use, the artificial buffer layer have been successfully removed, indicating that the
proposed hybrid approach is insensitive to the choices of the forcing region or interface
location. The predictive performance of the dynamic forcing scheme has been
further evaluated by considering turbulent flows subjected to a special type of body
force, i.e., the non-inertial and non-conservative Coriolis force. Due to the effects of
system rotation, turbulence level is enhanced on the pressure side and suppressed on
the suction side of the rotating channel. Furthermore, it is reported in this thesis
that the classification of the roughness type now relies not only on the pitch ratio,
but also on the rotation number in the context of rotating rib-roughened flows.
Description
Keywords
Turbulence modelling, CFD, LES, Hybrid RANS/LES
Citation
Q.-Q. Xun and B.-C. Wang. A dynamic forcing scheme incorporating backscatter for hybrid simulation. Physics of Fluids, vol. 26, no. 075104, pp. 1--27, 2014.