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#1 |
Senior Member
Nejc
Join Date: Feb 2017
Location: Slovenia
Posts: 196
Rep Power: 9 ![]() |
I tried to run a DNS case (i managed to get cell size small enough and geometry is fairly simple) only to find out dnsFoam only solves 'box' geometry.
I guess there's a reason for this? |
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#2 |
Senior Member
Uwe Pilz
Join Date: Feb 2017
Location: Leipzig, Germany
Posts: 744
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dnsFoam uses a spectral method for solving the case. This requires a rectangular mesh, all cell sizes equal and the cell count a power of 2.
You may use paraFoam instead and make the spatial and time resolution as small as the Kolmogorov scale requires. The dissipation rate eps disappears in this case (= gets very small).
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Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950) |
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#3 |
Senior Member
Nejc
Join Date: Feb 2017
Location: Slovenia
Posts: 196
Rep Power: 9 ![]() |
Oh I see.
Thanks for the tip - but are you sure you meant paraFoam? Could that be the reason that simpleFoam with k-Epsilon model blows up with very small cell sizes? I'm not really sure what's going on because everything was fine with triangular mesh with slightly bigger cells (just above Kolmogorov scale). Now I used blockMesh with sizes around 0.1x Kolmogorov scale and strange anomalies in pressure and velocity occur in one spot. |
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#4 |
Senior Member
Uwe Pilz
Join Date: Feb 2017
Location: Leipzig, Germany
Posts: 744
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simple Foam is not suited for transient cases. icoFoma doesn't have turbulence at all. pimpleFoam makes large time steps and corrects afterwards.
From the standard incompressible solvers only pisoFoam remains.
__________________
Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950) |
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#5 |
Senior Member
Nejc
Join Date: Feb 2017
Location: Slovenia
Posts: 196
Rep Power: 9 ![]() |
pisoFoam it is then.
I guess I can't use simpleFoam even though it is a steady-state case (a gap in plain bearings)? Thanks for your help. |
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#6 | |
New Member
Shantanu S Gulawani
Join Date: Aug 2018
Posts: 1
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Quote:
How do you find that it is a spectral code? or that it uses spectral method? I also want to know what is time discretization scheme in this solver? |
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#7 | |
Senior Member
Robert
Join Date: May 2015
Location: Bremen, GER
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Quote:
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#8 | |
Senior Member
Santiago Lopez Castano
Join Date: Nov 2012
Posts: 354
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Quote:
The requirements on the mesh come from the Kmesh class, that is used to generate the K field, which is used to generate a pseudo-random force. |
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