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-   -   Boundary condition for point? (http://www.cfd-online.com/Forums/fluent/31116-boundary-condition-point.html)

J.W.Ryu March 18, 2003 18:20

Boundary condition for point?
 
Hello,

I generated "point" from "surface/point" command, and I'd like to assign constant temperature for this point. Is it possible to assign boundary condition for specific point? I read manual several times. But, I could not find any appropriate method. Could you let me know the way?

Thanks,

J.W.Ryu

Alex Munoz March 18, 2003 21:50

Re: Boundary condition for point?
 
hello

Until I know you assign boundary conditions for zones.

Potentially could be one way, However, I want to know why you want just one point instead of a whole zone. If you expand a little bit your case perhaps I can help you more.

Regards

Alex

Chetan Kadaki March 20, 2003 04:47

Re: Boundary condition for point?
 
A point is a surface but not a zone. You must assign a b.c. to a zone. The best way to do this is in Gambit, just as you may have created your other b.c.'s.

But do tell why you just want one a single point at constant temp? Maybe then, we could advise better.


J.W.Ryu March 20, 2003 16:48

Re: Boundary condition for point?
 
My model is for steady state 2d-axisymmetry solidification. Of course, energy, DO model and standard k-e viscous model are being used. I gave Cp based on latent heat of fusion for liquid phase. But, calculation is not easy since temperature of liquid region is not constant during calculation. So, I'd intentionally like to give bc for specific point where solidification is happened. Specific point means tri-point of solid/liquid/gas phases. Of course, I can not image exact solificiation line, since this is decided by calculation from heat radiation, convection and conduction. Only I can aware specific point in solidification line. So, I wanna try to give bc(temperature) for specific point. Is this enough to explain my model? It is not easy to explain without any picture....

Thanks,

J.W.Ryu

Alex Munoz March 20, 2003 20:51

Re: Boundary condition for point?
 
I suggest that you use a UDF to define viscosity dependent of the temperature throught the the domain, instead of the boundary condition in some cells.

I wonder if you have read the solidification/melting model information offered by Fluent

Bellow you will see a UDF copied from Fluent

/************************************************** *******************

UDF for specifying a temperature-dependent viscosity property ************************************************** ********************/

#include "udf.h"

DEFINE_PROPERTY(cell_viscosity, cell, thread) { real mu_lam; real temp = C_T(cell, thread);

if (temp > 288.)

mu_lam = 5.5e-3; else if (temp > 286.)

mu_lam = 143.2135 - 0.49725 * temp; else

mu_lam = 1.;

return mu_lam; }

regards

Alex Munoz

J.W.Ryu April 6, 2003 23:45

Re: Boundary condition for point?
 
Thanks for your comment, Alex,

I also have used temperature dependent viscosity as mentioned in manual. But, as I mentioned before, liquid zone was not converged due to continuously changed temperature during iteration. As a solidification phenomina, I have used UDF to change source term of momentum equation to control liquid flow dependent on temperature. It showed analogous divergence trouble, since fluid flow and heat transfer are being solved at same time. During calculation, temperature of liquid zone is various so that viscosity/momentun source is continuosly changed. This affects next calculation repeatedly. Finally calculation was divergent. Could you let let me know appropriate method to overcome this trouble?

Thanks,

J.W.Ryu


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