[Venky_94]

Hey,

I'm writing a UDF to calculate the viscosity of one of the phases in a multiphase simulation. I've hooked the UDF using DEFINE_PROPERTY macro and I know the code works properly but I want to define it using the DEFINE_ADJUST macro as I want the store the value in a UDM which I can access in the other UDFs.

I'm getting errors of "uninitialized local variable 't' used" and "uninitialized local variable 'c' used". I understand that it means that the thread pointer is not defined, but I'm not quite sure how to rectify it.

I want to access the cell thread that will be passed to the UDF in the case of hooking it by material properties tab, but I'm not quite sure how to achieve that. Any help would be appreciated.

/******************************************************************************
UDM for storing the non-Newtonian fluid viscosity calculated using APL model
*******************************************************************************/

#include "udf.h"

DEFINE_ADJUST(non_newtonian_viscosity_udm, domain)
{
Thread *t, *pt;
Thread *mixture_thread = THREAD_SUPER_THREAD(t);
pt = THREAD_SUB_THREAD(mixture_thread, 0);
cell_t c;
domain = Get_Domain(2);		/*Defines the primary phase which is the non-Newtonian fluid */

/* Declare the coefficients for APL model to calculate non-Newtonian viscosity */
real mu_0 = 15.9350;
real k = 19.5531;
real n = 0.2891;
real p = -1.00;
real shear_rate;

/* Calculate the viscosity and store in UDM */
shear_rate = C_STRAIN_RATE_MAG(c,pt);
C_UDMI(c,pt,0) = pow((pow(mu_0,p) + pow((k*pow(shear_rate, (n-1))),p)),pow(p,-1));
}

[pakk]

Thread *thread = Lookup_Thread(domain, ID);

(copied from the manual)

[Venky_94]

Originally Posted by pakk

Thread *thread = Lookup_Thread(domain, ID);

(copied from the manual)

I'm aware of that command but I do not understand the difference between Domain ID and Zone ID. I'm running a multiphase simulation and I need my loop to run only on the thread pertaining to one phase (similar to hooking a UDF using a material properties tab).

I know that the domain ID for the phase is 2 from the "Phases" tab. But I'm unsure of the cell zone ID as there are two cell zones (with IDs 3 and 4) and both contain both fluids.

Also is any thread pointer passed by the solver at all when using a DEFINE_ADJUST macro by default?

[pakk]

You can see what is passed by looking at the function header:

DEFINE_ADJUST(non_newtonian_viscosity_udm, domain)

The only thing that is passed is the domain. So you don't need to get the domain yourself anymore.

But you do have to 'select' cell zones. If you have two cell zones, why don't you just use both?

[Venky_94]

Originally Posted by pakk

You can see what is passed by looking at the function header:

DEFINE_ADJUST(non_newtonian_viscosity_udm, domain)

The only thing that is passed is the domain. So you don't need to get the domain yourself anymore.

But you do have to 'select' cell zones. If you have two cell zones, why don't you just use both?

The domain that is passed with the DEFINE_ADJUST macros is the mixture domain, and I want the phase domain in my case which is why I'm specifying a domain.

Also how do I select multiple cell zones? I can select a cell zone using the LOOKUP_THREAD command, but I'm not sure how to select multiple zones.

/* Calculate the viscosity and store in UDM */
shear_rate = C_STRAIN_RATE_MAG(c,pt);
C_UDMI(c,pt,0) = pow((pow(mu_0,p) + pow((k*pow(shear_rate, (n-1))),p)),pow(p,-1));

Or should I perform the same calculation again for the other zone after obtaining the corresponding thread using LOOKUP_THREAD command?

[pakk]

Originally Posted by Venky_94

The domain that is passed with the DEFINE_ADJUST macros is the mixture domain, and I want the phase domain in my case which is why I'm specifying a domain.

OK, I don't have much experience in mixtures in UDFs. Maybe this is correct, but it feels strange.

Also how do I select multiple cell zones? I can select a cell zone using the LOOKUP_THREAD command, but I'm not sure how to select multiple zones.

/* Calculate the viscosity and store in UDM */
shear_rate = C_STRAIN_RATE_MAG(c,pt);
C_UDMI(c,pt,0) = pow((pow(mu_0,p) + pow((k*pow(shear_rate, (n-1))),p)),pow(p,-1));

Or should I perform the same calculation again for the other zone after obtaining the corresponding thread using LOOKUP_THREAD command?

The last option : just do it twice.

[Venky_94]

Originally Posted by pakk

OK, I don't have much experience in mixtures in UDFs. Maybe this is correct, but it feels strange.

The last option : just do it twice.

I used a cell thread and cell loop and it works fine now

I'm writing another UDF to store area-averaged phase fraction of air in a UDM. I need to obtain the phase level thread pointer st for which I'm using the THREAD_SUB_THREAD command and it requires the mixture-level thread as an argument. DEFINE_ADJUST unfortunately doesn't pass the thread pointer as an argument and only allows to loop over all threads in the domain.

I'm using the Lookup_Thread command to get a mixture-level thread pointer. I need the same thread pointer that will be passed by the solver within DEFINE_ADJUST if I'm looping over all threads in the domain. Would my below approach guarantee that, or do I need to specify some particular ID?

#include "udf.h"
#define ID 1						/* zone ID for the interior */

DEFINE_ADJUST(phase_fraction_udm, domain)		/* domain is defined as the mixture-level domain by default */
{
Thread *t, *st;
t = Lookup_Thread(domain, ID);				/* define the mixture-level thread to be used for identifying the secondary phase thread pointer */
st = THREAD_SUB_THREAD(t, 1);				/* st is the thread pointer for secondary phase i.e. air */