# Different flow pattern between OpenFOAM and CFX

 Register Blogs Members List Search Today's Posts Mark Forums Read

January 12, 2010, 08:08
Different flow pattern between OpenFOAM and CFX
#1
Member

Join Date: Sep 2009
Posts: 45
Rep Power: 9
Dear Foamers,

I'd like to validate OpenFOAM by using CFX. I use the same mesh and boundary conditions in both software. The same Reynolds number of 300,000. The LES Smagorinsky in CFX using the default damping function (with Cs=0.1) and Scalable as wall function; The LES Smagorinsky in OpenFOAM is shown as:

LESModel Smagorinsky;

delta cubeRootVol;

printCoeffs on;

cubeRootVolCoeffs
{
deltaCoeff 1;
}

vanDriestCoeffs
{
delta cubeRootVol;
cubeRootVolCoeffs
{
deltaCoeff 1;
}

smoothCoeffs
{
delta cubeRootVol;
cubeRootVolCoeffs
{
deltaCoeff 1;
}

maxDeltaRatio 1.1;
}

Aplus 26;
Cdelta 0.158;
}

smoothCoeffs
{
delta cubeRootVol;
cubeRootVolCoeffs
}

Where can I modify the Cs in OpenFOAM?
Moreover, I don't use any wall functions.
The inlet used in CFX is: Normal Speed 1m/s
The inlet used in OpenFOAM is:
INLET
{
type turbulentInlet;
fluctuationScale (0.01 0.01 0.01);
referenceField uniform (1 0 0);
alpha 0.1;
value uniform (1 0 0);
}
I created a cyclic patch in OpenFOAM to match the periodic BC of CFX.
I set pointSync to false and matchTolerance to 0.2.
Regarding the discretiztion schemes:
in CFX: Advection Scheme: Central Difference.
Transient Scheme: Second Order Backward Euler
in OpenFOAM: ddtScheme: backward
others: Gauss linear

The flow pattern is not the same: in CFX, no separation occurs on the top of the cylinder, which is good for a Reynolds number of 300,000.However, in OpenFOAM, a separation with no reattachment can be seen as if the Reynolds number was less enough from 300,000. I do not know where this difference can come from.
If anyone see something I should change in my setting, it would be great .

Thanks a lot,
AirS.
Attached Images
 case.jpg (9.2 KB, 130 views)

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post marco FLUENT 13 February 18, 2015 00:19 Valle OpenFOAM 0 August 26, 2009 08:12 marco Main CFD Forum 81 March 31, 2009 14:22 waynezw0618 OpenFOAM Running, Solving & CFD 39 March 5, 2009 13:57 CFD CFX 14 May 26, 2008 11:56