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-   -   UDF compute residence time session Id 619 (http://www.cfd-online.com/Forums/fluent-udf/63330-udf-compute-residence-time-session-id-619-a.html)

lisa April 5, 2009 10:13

UDF compute residence time session Id 619
 
Hi..

I am looking for UDF to compute residence time with the session ID 619. Can anyone post the code when u have.

Thanks in advance
Sesan.

coglione April 6, 2009 05:31

Here it is:

#include "udf.h"

/*
* UDF to compute fluid residence time
*
* by William Wangard, Ph.D.
* Fluent, Inc.
*
*/

/*
* This UDF requires at least 1 UDS to be defined
* At inlet, define UDS (value) = 0
* UDS will have units of time and represent approximate residence time
* of fluid in domain
*
* Diffusivity of scalar should be small to reduce diffusion i.e. 1E-5
*
*/


DEFINE_SOURCE(rt_source,c,t,dS,eqn)
{
real source = C_R(c,t);
dS[eqn] = 0.0;
return source;
}

cheers

Many January 21, 2016 08:25

Hi CFD friends!

I am trying to compute residence time contours using this kind of UDF.

My questions are the following:

1. Changing the mesh, then the residence time contours change (at least the maximum of residence time). I guess this is not desirable. Anybody has an idea about why this is happening? I realized that mesh cells appear in the function...

I am wondering if achieving mesh independent results will fix this, it's to said, max_residence_time tends to real_max_residence_time as cell_size tends to zero

If not, I am not understanding the value of this UDF as residence time will be mesh-dependent...

2. Which values should I use for Schmidt number and mass diffusivity for water?

3. When I got convergent results, I just solve for the defined scalar in steady state. Is unsteady solution needed? In other words, have I switch to unsteady model just for solving the scalar transport?

Thanks in advance for all your answers. I am a beginner in UDF...

Regards,

Many


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