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parabolic flow derivation

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dear all

i'm particularly new to comsol, and currently using comsol 3.3.

i'm interested in the fluid dynamics side of things, and understand that comsol uses this equation as the boundary equation for initial velocity (if using the inlet velocity) to describe a parabolic flow:

4*vmax*s*(1-s)

the multiplier is 6 if using vmean.

my question is: how is this derived? i know how the equation for a steady state flow in a circular pipe looked like, and it's nothing remotely similar to the above equation. and what is 's', by the way?

thanks for reading.

-nahrizul

3 Replies Last Post 12.06.2010, 05:13 GMT-4

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Posted: 1 decade ago 10.06.2010, 07:46 GMT-4
It is to enter a parabolic velocity profile:

bit.ly/a6Etlu

s is the Arc Length parameter. Take a boundary line, 0 is the beginning of the vector and 1 is the end of it. Something like y/H.
It is to enter a parabolic velocity profile: http://bit.ly/a6Etlu s is the Arc Length parameter. Take a boundary line, 0 is the beginning of the vector and 1 is the end of it. Something like y/H.

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Posted: 1 decade ago 11.06.2010, 12:23 GMT-4
hi danial

thanks for the quick response :-)

hi danial thanks for the quick response :-)

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 12.06.2010, 05:13 GMT-4
Hi

Just check regularly that "s" is really going from 0, to 1, this is MOSTLY the case, but I have had some surprises !

in 3D with s1, s2 its slightly more complex, and one should there too check regularly the ranges

It's just to plot "s" along the arc

Note that with V4 there are sometimes changes in the directions (flip of 0, and 1) w.r.t. 3.5 and the depending on the geometry, old habits should be renewed/updated with V4 ;)

Have fun Comsoling
Ivar
Hi Just check regularly that "s" is really going from 0, to 1, this is MOSTLY the case, but I have had some surprises ! in 3D with s1, s2 its slightly more complex, and one should there too check regularly the ranges It's just to plot "s" along the arc Note that with V4 there are sometimes changes in the directions (flip of 0, and 1) w.r.t. 3.5 and the depending on the geometry, old habits should be renewed/updated with V4 ;) Have fun Comsoling Ivar

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