On Jul 8, 7:38=A0pm, "Janes" <dja...@[EMAIL PROTECTED]
> wrote:
> I was asked today if I'd ever prepped a Pro/e model for analysis by CFD.
=
I say yes and told them basically how you prep a model for Mechanica
analys=
is (suppress rounds, holes, chamfers) to avoid me****ng small features. Not
=
hearing any gasps or depressed sighs in the background, I figured I was
pre=
tty close. But, the more I thought about this, the more I realized that
flu=
ids running through pipes under pressure have little to do with the
externa=
l features like rounds and chamfers. And least likely that you'd eliminate
=
holes where you're looking for cavitation in simulation. So, what kind of
p=
rep is done to models for CFD?
>
> David Janes
As you state, avoiding extremely small features that aren't likely to
affect the flow helps a lot in me****ng the geometry in the same way as
me****ng an FEA model. Tiny surfaces, gaps caused by poor modeling
(geom checks, tolerance settings) will also cause problems.
On the other hand if they are large relative to the size of the flow
field being modeled, rounds, chamfers, leak gaps, holes, bolt heads,
etc can have a big effect on the flow results so they may be necessary
to get accurate CFD results.
Real assemblies may have small clearances or gaps that in reality leak
flow. If these leak gaps are small relative to the flow field of
interest it may be desirable to eliminate them from the model. This
requires some judgment or simple 1D calculation to determine whether
the leakage is im****tant to the flow results of interest.
It depends on the me****ng tool used, but often a solid model of the
fluid must be constructed. This can be done by using the solid model
of the part to cut a fluid volume.
Finally, it is usually desirable to extend the fluid zone inlet and
exit length so that the flow boundary conditions at the inlet and exit
are separated from the region of interest. This requires either adding
actual upstream and downstream geometry to the model, or creating some
simplified geometry that mimics the effective area and perhaps the
flowpath curvature of the actual geometry.
Dave
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