CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Post-Processing

Function objects in multiphase flow

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

Reply
 
LinkBack Thread Tools Display Modes
Old   February 12, 2016, 09:40
Default Function objects in multiphase flow
  #1
Senior Member
 
ArielJ
Join Date: Aug 2015
Posts: 122
Rep Power: 3
arieljeds is on a distinguished road
Hi everyone,

I'm running a multiphase case with regular waves (using waveFoam) passing a vertical surface piercing cylinder and I'm trying to calculate the forces and force coefficients. I have them set up and they are being calculated and in the right place, but the values look very very wrong.

1) First of all, the values for the drag and lift coefficients are oscillating... does this suggest that they are not converging? I expected to see one value after the wave has reached the cylinder. The values not only are changing, but massively increase.

2) Is it even possible to use the forces and forceCoeffs function objects as they are with a multiphase solver?? I'm wondering if I have defined the phases incorrectly? Or if I need to separate the U and p values somehow into U.water and U.air, etc?

For instance, I am confused in my transportProperties file because I have the transport model set to Newtonian, so I commented out all other information (BirdCarreauCoeffs, CrossPowerLawCoeffs), as shown below:

Code:
phases (water air);

water
{
    transportModel  Newtonian;
    nu              nu [ 0 2 -1 0 0 0 0 ] 1e-06;
    rho             rho [ 1 -3 0 0 0 0 0 ] 1028;
    /*
    CrossPowerLawCoeffs
    {
        nu0             nu0 [ 0 2 -1 0 0 0 0 ] 1e-06;
        nuInf           nuInf [ 0 2 -1 0 0 0 0 ] 1e-06;
        m               m [ 0 0 1 0 0 0 0 ] 1;
        n               n [ 0 0 0 0 0 0 0 ] 0;
    }

    BirdCarreauCoeffs
    {
        nu0             nu0 [ 0 2 -1 0 0 0 0 ] 0.0142515;
        nuInf           nuInf [ 0 2 -1 0 0 0 0 ] 1e-06;
        k               k [ 0 0 1 0 0 0 0 ] 99.6;
        n               n [ 0 0 0 0 0 0 0 ] 0.1003;
    }
    */
}

air
{
    transportModel  Newtonian;
    nu              nu [ 0 2 -1 0 0 0 0 ] 1.568e-05; //1.48e-05;  --> current measurement for kinematic viscosity found at engineeringtoolbox.com
    rho             rho [ 1 -3 0 0 0 0 0 ] 1;
    /*
    CrossPowerLawCoeffs
    {
        nu0             nu0 [ 0 2 -1 0 0 0 0 ] 1e-06;
        nuInf           nuInf [ 0 2 -1 0 0 0 0 ] 1e-06;
        m               m [ 0 0 1 0 0 0 0 ] 1;
        n               n [ 0 0 0 0 0 0 0 ] 0;
    }

    BirdCarreauCoeffs
    {
        nu0             nu0 [ 0 2 -1 0 0 0 0 ] 0.0142515;
        nuInf           nuInf [ 0 2 -1 0 0 0 0 ] 1e-06;
        k               k [ 0 0 1 0 0 0 0 ] 99.6;
        n               n [ 0 0 0 0 0 0 0 ] 0.1003;
    }
    */
}

sigma           sigma [ 1 0 -2 0 0 0 0 ] 0.00;

My forces file is:

Code:
forces_object
{
    type            forces;  
    functionObjectLibs ( "libforces.so" );

    enabled         true;
    outputControl   timeStep;
    outputInterval  1;

    pName           p;
    UName           U;	
    rhoName         rhoInf; 	// Incompressible solver
    log             on;

    
    rhoInf      1.0;    	// Fluid density
    patches     ( cylinder); 

    CofR        (0 0 0);
    pitchAxis   (0 0 1);	// Gives moment coefficient

}
And forceCoeffs file:

Code:
forceCoeffs_object
{
	type 	forceCoeffs;
	functionObjectLibs ("libforces.so");
	patches (cylinder);

	pName 	p;
	Uname 	U;
	rhoName rhoInf;				// Reference Density 
	rhoInf  1.0;				// Density/1000
	
	log 	true;				// Dump to file -- change to false to not save a file 

	CofR 	(0.0 0 0);			// Centre of rotation 
	liftDir (0 1 0);			// Direction of lift coefficient  ---> y-direction (transverse to flow)   ?????
	dragDir (1 0 0);			// Direction of drag coefficient  ---> drag acts in opposite direction to flow (-x) 
	pitchAxis (0 0 1);			// Pitch moment axis  --> changed from pitchAxis (0 0 1)
	magUInf 0.4622;				// free stream velocity magnitude 
	lRef 6.0;         			// reference length (cylinder diameter)
	Aref 1.488;         			// reference area: lref * zmesh (zmesh is approx. pi*D/76)

        outputControl   timeStep;
        outputInterval  1;
}
I would really appreciate any help on this, I know it's a basic application but I am still very new to Openfoam and cfd and am struggling to find an explanation to help me understand what is going on.
arieljeds is offline   Reply With Quote

Old   February 17, 2016, 09:47
Default
  #2
Senior Member
 
ArielJ
Join Date: Aug 2015
Posts: 122
Rep Power: 3
arieljeds is on a distinguished road
Hi, I'm posting again here because I'm still having the same issue! I am calculating hugely incorrect drag coefficients (I am expecting typical values for a cylinder in waves and am getting a fluctuating drag coefficient with an average at -2,6222!

Some of my files are posted in the previous post so I won't repost. Can anyone please please offer advice on getting the drag coefficient?? I am so confused about why the values are so crazy! Please help!
arieljeds is offline   Reply With Quote

Reply

Tags
force coefficients, forces, free surface flow, functionobjects, multiphase

Thread Tools
Display Modes

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 Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to define to right point for locationInMesh Mirage12 OpenFOAM Native Meshers: snappyHexMesh and Others 7 March 13, 2016 15:07
Incorrect results of SWAK4FOAM function objects if Parallelisation involved wstapel OpenFOAM Running, Solving & CFD 0 December 17, 2015 10:57
Calculating mass flow rate at multiphase flows Kuslo187 OpenFOAM Post-Processing 1 August 21, 2015 18:11
swak4Foam installation problem Claudio87 OpenFOAM 9 May 8, 2013 10:20
non-orthogonal faces and incorrect orientation? nennbs OpenFOAM Native Meshers: blockMesh 7 April 17, 2013 05:42


All times are GMT -4. The time now is 02:48.