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-   -   OpenFOAM verification abrupt area change (http://www.cfd-online.com/Forums/openfoam-solving/58508-openfoam-verification-abrupt-area-change.html)

mkraposhin October 2, 2008 04:11

Dear OpenFOAM users! I've s
 
Dear OpenFOAM users!

I've started verification of OpenFOAM with abrupt area change studies. The goal - is to calculate total pressure loss and compare it with experimental data.

I found, that for sudden expansion i have difference 3-15%, which is normal

but for sudden contraction difference for loss coefficient is bigger then 20%, this is unsatisfactory.

below are formulas for loss coefficients

Cf_contraction = dP_tot/(w0^2/2)=0.5*(1-F0/F1) (1)
Cf_expansion = dP_tot/(w0^2/2)=(1-F0/F1)^2 (2)

where F0 - area with small section
F1 - area with large section
w0 - average velocity in section F0

formulas (1) and (2) obtained from Idelchik; this formulas has been used for many years, so, i think, they are right

for example, for F0/F1
Cf_expansion=0.25=Cf_contraction=0.25

My values are much larger!
What i am doing wrong?

y+ varies from 20 to 90 in both cases
turbulenceModel = k-omega SST with wall-functions

contraction case:
http://www.cfd-online.com/OpenFOAM_D...ges/1/9403.jpg

expansion case
http://www.cfd-online.com/OpenFOAM_D...ges/1/9404.jpg

Sorry for bad English!


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