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June 19, 2013, 04:21 
icofoam = DNS?

#1 
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Dongyue Li
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hey guys,
In OpenFOAM, icofoam solve NS equations with no additional models, AFAIK, its the same with DNS, so can I use icoFoam to simulate turbulence? Just by set delta t is very small such as:1e7? Thanks. 

July 2, 2013, 23:05 

#2 
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Santiago Marquez Damian
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Santiago MÁRQUEZ DAMIÁN, Ph.D. Research Scientist Research Center for Computational Methods (CIMEC)  CONICET/UNL Tel: 543424511594 Int. 7032 Colectora Ruta Nac. 168 / Paraje El Pozo (3000) Santa Fe  Argentina. http://www.cimec.org.ar 

July 8, 2013, 23:33 

#3  
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Dongyue Li
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Quote:
I know there is a dnsFoam, but to my experience and Versteeg's book page 110: Code:
The instantaneous continuity and Navier–Stokes equations (3.23) and (3.24a–c) for an incompressible turbulent flow form a closed set of four equations with four unknowns u, v, w and p. Direct numerical simulation (DNS) of turbulent flow takes this set of equations as a starting point and develops a transient solution on a sufficiently fine spatial mesh with sufficiently small time steps to resolve even the smallest turbulent eddies and the fastest fluctuations. Anyway Im not familar with dnsDoam. Thanks. 

July 9, 2013, 00:04 

#4 
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Santiago Marquez Damian
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If you check the code for dnsFoam you will see that it is similar to icoFoam, except for a source term which adds turbulence to the system. Without it the problem would evolve to a resting system due the dissipative effect of the viscosity.
Regards
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Santiago MÁRQUEZ DAMIÁN, Ph.D. Research Scientist Research Center for Computational Methods (CIMEC)  CONICET/UNL Tel: 543424511594 Int. 7032 Colectora Ruta Nac. 168 / Paraje El Pozo (3000) Santa Fe  Argentina. http://www.cimec.org.ar 

February 1, 2014, 20:18 

#5  
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Quote:
1)should we except same result if we solve a laminar case by icoFoam and dnsFoam?Does that extra source term influences on the result for a laminar case? 2)Is there any difference between the cost of dnsFoam and icoFoam for a identical laminar test case? for example that extra source term might decrease the cost or not...? Thanks in advance 

March 7, 2014, 23:48 

#6 
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Santiago Marquez Damian
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Hi,
1) It depends on the relative intensity of the source term, but in general, yes. 2) They are the same solvers, the source terms add a little more cost. Regards
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Santiago MÁRQUEZ DAMIÁN, Ph.D. Research Scientist Research Center for Computational Methods (CIMEC)  CONICET/UNL Tel: 543424511594 Int. 7032 Colectora Ruta Nac. 168 / Paraje El Pozo (3000) Santa Fe  Argentina. http://www.cimec.org.ar 

March 17, 2014, 07:08 

#7  
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Huang Xianbei
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Quote:
Ichecked the DNS solver and found a force add to the r.h.s of the UEqn, and find the definition: Code:
volVectorField force ( U/dimensionedScalar("dt", dimTime, runTime.deltaTValue()) ); I've looked into someone's code in this forum about channel flow DNS, the 'force' is not added, so I'd like to know is it necessary to do so? 

June 8, 2014, 05:01 

#8 
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Florian Ries
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Hi,
in the description of dnsFoam.c you can find: Application dnsFoam Description Direct numerical simulation solver for boxes of isotropic turbulence In my opinion you only need this force, if you don't have shear or a wall that gives you shear. So dnsFoam is proper for the boxturb16 and for no other case. In the tutorial of Martin de Mare, he mentioned that the force term is to keep the turbulence alive. You only need this force, if you have no shear of e.g.shear at a wall? Because if you have a wall, turbulence keep alive by the shear, right? I want to simulate a quasiDNS of pipeflow. From the description, dnsFoam solver is for DNS of isotropic turbulence in boxes. So this solver is not suitable for my case. Now my question: Is icoFoam the right solver for DNS in complex geometries with shear at a wall?? kind regards Florian 

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