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A dynamic global-coefficient mixed subgrid-scale eddy-viscosity model
for large-eddy simulation of turbulent flows in complex geometries is
developed. In the present model, the subgrid-scale stress is decomposed
into the modified Leonard stress, cross stress, and subgrid-scale Reynolds
stress. The modified Leonard stress is explicitly computed assuming a scale
similarity, while the cross stress and the subgrid-scale Reynolds stress
are modeled using the global-coefficient eddy-viscosity model. The model
coefficient is determined by a dynamic procedure based on the
global-equilibrium between the subgrid-scale dissipation and the viscous
dissipation. The new model relieves some of the difficulties associated
with an eddy-viscosity closure, such as the nonalignment of the principal
axes of the subgrid-scale stress tensor and the strain rate tensor and the
anisotropy of turbulent flow fields, while, like other dynamic
global-coefficient models, it does not require averaging or clipping of the
model coefficient for numerical stabilization. The combination of the
global-coefficient eddy-viscosity model and a scale-similarity model is
demonstrated to produce improved predictions in a number of turbulent flow
simulations.
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