Computational Fluid Dynamics
Lecture 22
Subgrid Scale Modeling
The two most significant difficulties in doing CFD are:
1. What to do with unresolved large scale motions.
2. How to treat unresolved small scale motions.
Typical grid resolutions possible on large computers in 2000 depend on the time duration of the
calculation, but for typical “midterm” calculations, say 10 eddy turnover times, or 10 hours or 10
days of simulation.
Grid resolutions of 256
256
256
×
×
are possible or common.
3
256
16.8
=
million grid points
This would allow simulation of a computational domain of ~50 km
50 km
5 km
×
×
with 100 m grid
resolution
or
~
with 1 mm grid resolution.
25 cm
25 cm
25 cm
××
In the large scale problem, there are a lot of sub grid scale processes.
The entire surface mixer layer is typically 100 m thick and strongly influences the transfer of
momentum and heat between the ocean and atmosphere.
Large scale ocean models, such as for the North Atlantic, cover domains of ~10,000
km
10,000 km
10 km
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 Spring '07
 Slinn
 Fluid Dynamics, Orders of magnitude, Computational fluid dynamics, eddy viscosity, Subgrid Scale Modeling

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