CFD Online Discussion Forums - Patching Volume Fraction in a sloped channel

CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)

- FLUENT (https://www.cfd-online.com/Forums/fluent/)

- - Patching Volume Fraction in a sloped channel (https://www.cfd-online.com/Forums/fluent/86469-patching-volume-fraction-sloped-channel.html)

Patching Volume Fraction in a sloped channel

Hello. I'm running an open channel VOF model of a sloped channel and would like to be able to patch a volume fraction of 1 for the area under the water surface. I understand how to do this in a flat channel using region adaption in Fluent. I can't however figure out how to do this for a sloped channel in which the water surface is also sloped at approximately the same angle as the channel bottom.

any suggestions?

Hi Katey,
you can do that with a simple UDF with DEFINE_INIT macro. loop over all cells and set a condition over y-coordinate ....

Thanks. I will look into that. I'm pretty new at this but I'm finding if I can't intialize the volume fraction for the water portion of the problem it takes a long time to get water through the channel.

Use of VOF Multiphase Macro

So in order to use the DEFINE_INIT macro I need to find the correct cell macro to initialize the volume fraction in the cell. I believe this is the C_VOF(c,t) macro but I'm a little confused about how to apply it...or I should say how to indicate which phase i'm changing, 1 or 2.

Any help is much appreciated.

Quote:

Originally Posted by KateyMT (Post 300909)

Hi,
the similar code is available in UDF manual that you can use it but your procedure is simpler:

Code:

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

UDF for initializing phase volume fraction

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

#include "udf.h"

/* domain pointer that is passed by INIT function is mixture domain */

DEFINE_INIT(my_init_function, mixture_domain)

{

int phase_domain_index;

cell_t cell;

Thread *cell_thread;

Domain *subdomain;

real xc[ND_ND];

/* loop over all subdomains (phases) in the superdomain (mixture) */

sub_domain_loop(subdomain, mixture_domain, phase_domain_index)

{

/* loop if secondary phase */

if (DOMAIN_ID(subdomain) == 3)

/* loop over all cell threads in the secondary phase domain */

thread_loop_c (cell_thread,subdomain)

{

/* loop over all cells in secondary phase cell threads */

begin_c_loop_all (cell,cell_thread)

{

C_CENTROID(xc,cell,cell_thread);

if (sqrt(ND_SUM(pow(xc[0] - 0.5,2.),

pow(xc[1] - 0.5,2.),

pow(xc[2] - 0.5,2.))) < 0.25)

/* set volume fraction to 1 for centroid */

C_VOF(cell,cell_thread) = 1.;

else

/* otherwise initialize to zero */

C_VOF(cell,cell_thread) = 0.;

}

end_c_loop_all (cell,cell_thread)

}

}

}

Thanks. I just found that and I'm running it now. Crossing fingers.