CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT

momentum source term

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

Like Tree3Likes
  • 1 Post By subha_meter
  • 1 Post By subha_meter
  • 1 Post By subha_meter

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 27, 2004, 23:00
Default momentum source term
  #1
zwdi
Guest
 
Posts: n/a
Hello everybody,

I am simulating species transportation with the source term in one fluid zone. I only have the clear mass (kg/m3-s) parameter from experiments. I don't know exactly momentum source parameter, Renold stress parameters(UU, UV,..) either. So I only add the mass source term in my simulation. In the period of iteration, Reverse Flow appears. The results diverged. I am thinking that if the reason is the missing of momentum source term , TKE, Dissipation source term, and Renold stress source term.

Could anybody tell me that the way I add the source term is right or wrong? I have no experiences for adding source term. Must I add each source term usually or some specific source terms depending on different cases?

Thanks in advance for your time and kindness.

Have good weekend.

Zwdi
  Reply With Quote

Old   September 28, 2010, 02:36
Default Adding momentum source terms in multiphase eulerian simulation
  #2
Member
 
subha_meter's Avatar
 
Subhasish Mitra
Join Date: Oct 2009
Location: Australia
Posts: 56
Rep Power: 17
subha_meter is on a distinguished road
Hello All,

I'm carrying out multiphase eulerian simulation in porous media to estimate pressure drop and liquid hold up. Addition of momentum source terms in both the phases (gas & liquid) have been reported in literature which I've incorporated through UDF as well however my simulation diverges pretty fast.

Momentum source terms:

Liq phase: (l)

(1-alpha)/k_liq*(A*Rel/Gal + B*Rel^2/Gal)*rho_l*g

Gas phaseg)

alpha/k_gas*(A*Reg/Gag + B*Reg^2/Gag)*rho_g*g

where alpha = gas vol fraction, A & B = Ergun co-eff, Re = Reynolds no, Ga = Galileo no, rho = density, g = 9.81 m/sec2
k = relative permeability for liq & gas phase


Gas phase momentum transfer UDF for example:

DEFINE_SOURCE(gas_phase_xmom_source,c,t,dS,eqn)
{

real x_vel_l, y_vel_l, abs_U, rho_l, drv1_g, drv2_g, Fg,drv,
mu_l, x_vel_g, y_vel_g, rho_g, mu_g, void_g, Reg, Gag, E0, eps, sg, kg, source;

/* find phase velocities and properties*/

x_vel_g = C_U(c,t);
y_vel_g = C_V(c,t);
rho_g = C_R(c,t); /*Gas Density*/
mu_g = C_MU_L(c,t); /*Gas Viscosity*/
abs_U=sqrt(x_vel_g*x_vel_g + y_vel_g*y_vel_g);
void_g = C_VOF(c,t); /* gas vol frac*/
Reg = rho_g*abs_U*dp/(mu_g*(1-ep));
Gag = pow(rho_g,2)*g*pow(dp,3)*pow(ep,3)/(pow(mu_g,2)*pow(1-ep,3));
E0 = rho_l*g*pow(dp,2)*pow(ep,2)/(sigma * pow((1-ep),2)); /*Eotvos no*/
eps = 1.0/(20.0 + 0.9*E0);/*static liq hold up*/
sg = 1.0 - eps/ep;
kg = pow(sg,4.80);

/*Momentum source Term*/

Fg = (void_g*rho_g*g/kg)*(E1*Reg/Gag + E2*pow(Reg,2)/Gag);

drv1_g = E1*rho_g*dp/(mu_g*(1-ep));
drv = rho_g*dp/(mu_g*(1-ep));
drv2_g = E2*2*abs_U*pow(drv,2);
source = Fg;

/* derivative of source term w.r.t. x-velocity. */

dS[eqn] = void_g*rho_g*g/kg*(drv1_g*E1*Reg/Gag + drv2_g*E2*pow(Reg,2)/Gag);

return source;
}


Is there any suggestion to correct it? Any suggestion will be highly appreciated.

Regards,

SM
Khunnie_baby likes this.
subha_meter is offline   Reply With Quote

Old   May 6, 2011, 14:46
Default porous media trickle bed
  #3
New Member
 
abhik banerjee
Join Date: Jul 2010
Location: Roorkee
Posts: 9
Rep Power: 16
abhik.banerjee is on a distinguished road
Hii Subha

I am working on trickle bed reactor with porous media concept exactly similar to your work. It seems like you have used momentum source terms instead of viscous resistance values. Or have you used both? Can you tell me which drag law you have applied for gas and liquid phase and the boundary conditions? It will be of great help as I am running out of time.
abhik.banerjee is offline   Reply With Quote

Old   May 7, 2011, 00:02
Default Trickle Bed Reactor_mometum source model
  #4
Member
 
subha_meter's Avatar
 
Subhasish Mitra
Join Date: Oct 2009
Location: Australia
Posts: 56
Rep Power: 17
subha_meter is on a distinguished road
Hello Avik,

Well, I've spent sometime to build up this model since this post however validation with experimental data is still pending. The porous media model can be built using both "viscous and inertial resistance" and "momentum source" (I strongly believe so).

In both case, you need closure equations from "Relative permeability model" of Saez and Carbonell (1985)-AICHE journal. You can either keep the porosity uniform or variable. If you want to vary it, then a radial porosity distribution function proposed by Mueller et al (1994) is suggested.

Hope it helps.
subha_meter is offline   Reply With Quote

Old   May 7, 2011, 00:08
Default Trickle bed reactor_porous media model
  #5
Member
 
subha_meter's Avatar
 
Subhasish Mitra
Join Date: Oct 2009
Location: Australia
Posts: 56
Rep Power: 17
subha_meter is on a distinguished road
Forgot to mention that you need to calculate boundary conditions by solving "phenomenological models" - proposed any of those by Holub et al(1992,1993), Larachi et al (1990), Wammes et al (1990,1991), Ellman et al (1990).

For gas-liquid interaction term, you can do the followings

--> use none considering loss against solid phase is much more than gas-liquid interaction

--> Use Attou et al's (1999) fluid fluid interaction model

Hope it helps

SM
subha_meter is offline   Reply With Quote

Old   May 7, 2011, 02:53
Default
  #6
New Member
 
abhik banerjee
Join Date: Jul 2010
Location: Roorkee
Posts: 9
Rep Power: 16
abhik.banerjee is on a distinguished road
Hii Subha

Thanks a lot for your reply.

Regarding the boundary conditions:
  1. I have specified velocity inlet and pressure outlet for 2 phase Eulerian-Eulerian model.. I have given 0.4 volume fraction of liquid phase(phase 2) at the inlet. The problem here is that I have to specify backflow volume fraction at pressure outlet. How to specify this value?What value have you taken? Did you choose pressure outlet or outflow condition?
  2. I have defined the fluid zone as porous media. I have to specify inertial and viscous resistance values for both the phases. Using the formula you have mentioned in other posts, the value comes out to be a single value. But if we use pressure drop vs velocity values from experimental data, we will have different values for both phases. How did you compute these values?
  3. If I am using momentum source UDF as you have mentioned, is it necessary to specify inertial and viscous resistance coefficients?
Your guidance regarding these issues will be of great help.
abhik.banerjee is offline   Reply With Quote

Old   May 7, 2011, 04:26
Default Trickle bed reactor_porous media
  #7
Member
 
subha_meter's Avatar
 
Subhasish Mitra
Join Date: Oct 2009
Location: Australia
Posts: 56
Rep Power: 17
subha_meter is on a distinguished road
Hello Abhik,

1. Using backflow volume fraction is tricky in FLUENT for E-E multiphase flow. I suggest to use "dispersed phase" i.e. secondary phase volume fraction to set "0" at outlet.

Outflow BC is used normally for unconfined flow and it never gives a good prediction of pressure drop. So a pressure outlet BC is always recommended.

2. For theoretical computation, if you use Ergun equation then you will get single value for resistances which is not correct. You need to calculate this resistances from Saez & Carbonell (1985) formulation which uses relative permeability for both phases and gives different resistances. And if you have experimental data for pressure drop then it's OK.

3. Modeling of porous media model using momentum source terms is another way if you do not use porous media module. It's mutually exclusive.

Hope it helps,

SM
sircorp likes this.
subha_meter is offline   Reply With Quote

Old   May 7, 2011, 05:02
Default
  #8
New Member
 
abhik banerjee
Join Date: Jul 2010
Location: Roorkee
Posts: 9
Rep Power: 16
abhik.banerjee is on a distinguished road
Hii Subha

The information in your reply is of great help.

If I am specifying momentum source UDF, then can I specify viscous coefficients as well along with this UDF or only one of these two should be used?
abhik.banerjee is offline   Reply With Quote

Old   July 17, 2013, 08:56
Default
  #9
New Member
 
Hanumanth
Join Date: Aug 2009
Posts: 6
Rep Power: 17
p08tm007 is on a distinguished road
In fluent there is only possibility of defining momentum source in either x,y & z directions. If we want to define momentum source over a cylinder, then how to do this in fluent. Hey guys please help me regarding this, as this option is not there in fluent.

Thanks in Advance...
p08tm007 is offline   Reply With Quote

Old   July 17, 2013, 20:05
Default momentum souce term
  #10
Member
 
subha_meter's Avatar
 
Subhasish Mitra
Join Date: Oct 2009
Location: Australia
Posts: 56
Rep Power: 17
subha_meter is on a distinguished road
I don't think it should be a problem for cylindrical geometry. In cylinder, we need to define the axial and radial momentum source terms which I believe can be done specifying the source term in 'y' direction to account for axial and 'x' & 'z" directions (should be same) to account for the radial change.
__________________
SM
subha_meter is offline   Reply With Quote

Old   December 4, 2013, 03:55
Default
  #11
New Member
 
Hanumanth
Join Date: Aug 2009
Posts: 6
Rep Power: 17
p08tm007 is on a distinguished road
Quote:
Originally Posted by subha_meter View Post
I don't think it should be a problem for cylindrical geometry. In cylinder, we need to define the axial and radial momentum source terms which I believe can be done specifying the source term in 'y' direction to account for axial and 'x' & 'z" directions (should be same) to account for the radial change.
Hi subha_meter, thanks for ur reply nd time. In my case, actually flow from the cylinder in radial direction. There is no axial flow. flow rate from the cylinder is 450 LPS. And the momentum source calculated comes out be 18.638. Can u plz explain me how to incorporate this in the fluent.

Thanks in Advance.
p08tm007 is offline   Reply With Quote

Old   December 4, 2013, 18:39
Default Momentum source term in cylindrical geometry
  #12
Member
 
subha_meter's Avatar
 
Subhasish Mitra
Join Date: Oct 2009
Location: Australia
Posts: 56
Rep Power: 17
subha_meter is on a distinguished road
If this momentum source term is constant, you need to enter this value to
cell zone condition--> fluid--> source term --> x and z momentum.

If this source term changes with velocity or any other parameters, you need to specify it using UDF (sample UDF for momentum source term is provided in FLUENT UDF manual).

Hope it helps,
ahmed banna likes this.
__________________
SM
subha_meter is offline   Reply With Quote

Old   December 5, 2013, 04:30
Default
  #13
New Member
 
Hanumanth
Join Date: Aug 2009
Posts: 6
Rep Power: 17
p08tm007 is on a distinguished road
Hi subha_meter, thanks for ur kind time. As my source term is constant. if i put this constant value in the x and z momentum source, then the flow from the cylinder comes out in the direction that is resultant of the x & z. But not in radial directions.

Can u plz help me out as early as possible. as i have t start the simulation.

Thanks in advance.
p08tm007 is offline   Reply With Quote

Old   December 5, 2013, 18:58
Default
  #14
Member
 
subha_meter's Avatar
 
Subhasish Mitra
Join Date: Oct 2009
Location: Australia
Posts: 56
Rep Power: 17
subha_meter is on a distinguished road
You need to realize that it's not possible to get direct access to radial direction in Cartesian Coordinate which is native to Cylindrical Coordinate system.

The radial direction can only be achieved in Cartesian system if you take resultant of X & Z direction (horizontal and radial plane) while keeping the Y axis perpendicular to the X & Z plane.

Alternatively, you can construct a 2D axisymmetric mesh (axis BC on the vertical/perpendicular axis -- X direction) and define the radial source term along the Y axis which should solve the problem.
__________________
SM
subha_meter is offline   Reply With Quote

Old   June 27, 2017, 16:40
Default segmentation fault
  #15
Member
 
sebastian bergman
Join Date: Mar 2017
Location: seattle
Posts: 52
Rep Power: 9
Tushar_Telmasre is on a distinguished road
In my momentum equation owing to density difference i have to write a source term udf. the source term is,

source term= - ρl.(1+∝).u ⃗ .∂fl/∂t

where ∝ = the volume of fraction variable
fl = liquid fraction
ul = Velocity vector
ρl and ρs = liquid and solid density respectively


I did write a udf for it

-----for x-momentum----
#include "udf.h"
#define rho_l 1544.0
#define rho_s 1648.0

DEFINE_SOURCE(x_momentum_source,c,t,dS,eqn)
{
real source;
source = -(rho_l*(1+C_VOF(c,t))*C_U(c,t)*((C_LIQF(c,t)-C_LIQF_M1(c,t))/CURRENT_TIMESTEP));
dS[eqn] = 0;
return source;
}

----for y-momentum-----
#include "udf.h"
#define rho_l 1544.0
#define rho_s 1648.0

DEFINE_SOURCE(y_momentum_source,c,t,dS,eqn)
{
real source;
source = -(rho_l*(1+C_VOF(c,t))*C_V(c,t)*((C_LIQF(c,t)-C_LIQF_M1(c,t))/CURRENT_TIMESTEP));
dS[eqn] = 0;
return source;
}


i hooked it in the cell zone section. i was using the VOF module.
IT is giving me a segmentation fault.
I am not able to understand the mistake here. can anybody help?
Tushar_Telmasre is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
[swak4Foam] swak4foam building problem GGerber OpenFOAM Community Contributions 54 April 24, 2015 17:02
pisoFoam compiling error with OF 1.7.1 on MAC OSX Greg Givogue OpenFOAM Programming & Development 3 March 4, 2011 18:18
Version 15 on Mac OS X gschaider OpenFOAM Installation 113 December 2, 2009 11:23
Pressure jump and momentum source Tanya FLUENT 1 June 4, 2009 16:22
Defining momentum source term with swirl...? Sushil FLUENT 0 September 24, 2007 05:41


All times are GMT -4. The time now is 17:10.