一段有关Fluent中LES的评价

wingman

(from:http://capella.colorado.edu/~laney/software.htm)

Commercial CFD software is a relatively new phenomenon, one that really only
got underway in the late 1980's. Even now, the typical CFD company is
relatively small and closely tied to academia. For a nice list of commercial
CFD companies, click here.

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The following, originally posted on CFD Online by "Andy," illustrates the
stengths and weaknesses typical of commercial software. Although this
concerns FLUENT specifically, similar things could be said of any commercial
CFD package.
"FLUENT is a general purpose code and can address a wide range of problems in
fluid mechanics. Although this generality can be what is needed it is also
the key to FLUENT's main failing: it cannot predict particular classes of
flows as well as CFD codes
written solely for that class of flow. That is, if you are only interested in
hypersonic flows then a CFD code written only to solve hypersonic flows can
be substantially more accurate and more efficient. However, the costs of
working effectively with
specialized codes are different to those of working with general purpose
codes. It can be higher or lower - the key is usually access to educated
people who know what they are doing. Perhaps using a bigger computer, waiting
longer for the answers and
accepting a higher risk that the answers are misleading is perfectly
acceptable. It depends on what you are using the code to achieve.

"A personal example: I recently considered proposing FLUENT for a set of LES
simulation (it has an LES button and could be driven by relatively
inexperienced people). After a phone call with FLUENT it became clear that:
"The code is very inefficient requiring around 30 times more computing time
per time step than a purpose written code. This figure is very approximate
but was based on a real prediction running within FLUENT at the time - I
could not believe the
computing resource it required.
"The low accuracy of the convection terms is a poor choice for LES. i.e.
requiring much too fine a grid to match a scheme which uses a more accurate
differencing scheme.
"It was not possible to generate curvilinear grids of a high enough quality.
Related to accuracy of convection terms (or perhaps not given the low
accuracy differencing!).
"The computer memory requirement was not investigated but it looked to be
around 10 times more.
"I was not convinced that FLUENT were on top of the problems of near wall
treatment for this type of flow since the parameters to control it were not
in evidence.
"To be fair, I think this should be recognised as something of an extreme
example caused by FLUENT adopting low accuracy differencing, unstructured
grids and general purpose implicit solvers for a class of flows which are
best served by high accuracy
differencing, structured grids and very simple efficient solvers.
"To conclude, I believe codes like FLUENT can help address a significant
range of engineering problems. However, they are best used by people who
understand their strengths and weaknesses and they are best not used in
isolation."

xfseu

说的是 学会了Fluent并不NB NB的是自己会编代码