[jjfm20]

Hello guys,

Hope you're well, I need to use the mass-average-weighted total temperature of an outlet as the backflow temperature input of the same outlet, I guess is kinda an iterative process but I don't have any clue of how to do so... Hope you can help me with steps or something like that.

Regards.

[sdarmayuda]

Hi,

I'm also facing a similar problem. I need to calculate the new rotational velocity based on the torque given from the last iteration. Have you found the solution? I'll be very grateful if you can share it here. Thanks.

Best regards,
Darma Yuda

[jjfm20]

Hi Darma Yuda,

I did solved it but it needed a UDF for the iterative part, you should check this possibility.

Regards.

[sdarmayuda]

Hi jjfm20,

Thanks for your reply. I see. Right now, I'm trying to simulate the fluid coupling which consist of pump and turbine side. The pump's rotational velocity is set to constant for now. And the turbine side should rotate because the torque from the fluid. (This torque will accelerate the turbine side). I have tried to write an UDF for this case but the udf is not right yet.

**********************************************
#include "udf.h"
#define Niter 25 /* iteration update interval */
#define omg_ts 0.0 /* starting omega */
#define omg_tf 600.0 /* final omega */
#define Jt 0.000554 /* Moment Inertia of the Turbin*/
#define delta_t 0.001 /* Delta-t Simulation */

DEFINE_ADJUST(testudf,domain)
{
int zoneID;
int iter = (nres==0)?(1):((int)count2[nres-1]);
float omgt;
Thread *tc;

zoneID = 2;
tc = Lookup_Thread(domain,zoneID);

if ( (iter%Niter)==0 )
{
Mt = 15*parameter-1; /*The moment was calculated per blade, There is 15 blade*/
del_omgt = Mt/Jt;
omgt = omg_ts + del_omg*(iter/Niter);
if ( omgt > omg_tf ) omgt = omg_tf;
THREAD_VAR(tc).fluid.omega = omgt;
}
}
******************************************

1. Do you mind pointing my mistakes from my UDF-code out? Or if you still have your UDF, do you mind sharing it?
2. Just to make sure, so will our UDF only be read by Fluent once at the beggining of the calculation? I thought at first that, this UDF will be read at every iteration.
I really appreciate your help. Thanks for your help once again.

Best regards,
Darma Yuda

[AlexanderZ]

Your UDF does nothing. You do not use any flow variable inside the code.
To see, if the UDF is hooked by fluent you may use Message functions.

Best regards.

[sdarmayuda]

Hi AlexanderZ,

Thanks for the reply. Can you give me some more tipps or referenz regarding this flow variable? http://jullio.pe.kr/fluent6.1/help/html/udf/node108.htm I should find the variable for the rotational velocity right? I can only find the velocity in u,v, w direction.

Actually I also am trying to input the torque resulted by the fluid into code, by i don't know how I could obtain the variable? Should I use the tool "Output Parameter" and create a new parameter? Or does Fluent already have a certain variable for this measurement? I'd be very grateful if you can give me some tipps. Thanks you very much once again.

Best regards,
Darma Yuda

[MKuhn]

Using calculated values from a outlet boundary in a inlet boundary works only with an UDF. The tool "output parameter" does'nt help.
This UDF calculateds first an average temperature at the boundary with the ID 24, which is the input for the calculation of the temperature for an inlet stream.

#include "udf.h"
DEFINE_PROFILE(calc_inlet_temp,thread,nv)
{
Domain *d;

real temp=0.;
real flux=0.;
real temp_in;
real temp_in_min = 183;

face_t f;
Thread *t;
d = Get_Domain(1);
t= Lookup_Thread(d, 24);

begin_f_loop(f,t)
{
flux+=F_FLUX(f,t);
temp+=F_T(f,t)*F_FLUX(f,t);
}
end_f_loop(f,t)

temp=temp/flux;

temp_in=2.0573E-5*temp*temp*temp-1.4976E-2*temp*temp+3.8548*temp-150.22;

if (temp_in < temp_in_min){temp_in=temp_in_min;}

begin_f_loop(f,thread)
{
F_PROFILE(f, thread, nv) = temp_in;
}
end_f_loop(f,thread)
flux=0.;
}

[sdarmayuda]

Hallo MKuhn,

Thank you very much for your help. I have adjusted my UDF Code to yours.

********************************
#include "udf.h"
DEFINE_ADJUST(testudf,d)
{
real omega_ts=0.0; /*starting omega*/
real omega_tf=600.0; /*final omega*/
real Jt=0.000554; /*Moment Inertia of the Turbin*/
real delta_t=0.0001; /*time step simulation*/
real alpha_t; /*angular acceleration, delta t*/
Thread *t;
cell_t c;
t=Lookup_Thread(d,9); /*Zone ID = 9*/
begin_c_loop (c,t)
{
alpha_t= Mt/Jt; /*M = J*alpha, but how can I retrieve the value of Mt?*/
omega_ts+=alpha_t*delta_t;
if (omega_ts > omega_tf)
{omega_ts = omega_tf;}
THREAD_VAR(t).fluid.omega=omega_ts; /*I'm not sure if this Syntax correct*/
}
end_c_loop (c,t)
}
*********************************

1. I think I should use cell loop instead of face loop, because it is about rotational velocity of the Body. Is that correct?

2. If the tool "Output Parameter" doesn't help, how should I retrieve the calculated torque Mt and input to my UDF Code? In your case, you have F_Flux(f,t). But I can't find a way to retrieve the torque working on the body.

3. So will this UDF Code be read/executed only once? Or will it be read every time step? I'm using delta_t= time step of my simulation. I assume that Fluent will read the part of my code from "begin_c_loop ..." until "end_c_loop(c,t)" at every time step. But I'm not so sure about that.


Thanks once again for your help and your code.

Best regards,
Darma Yuda

[MKuhn]

Hello sdarmayuda

Sorry but I'm not an expert in UDF, I just adopted an existing UDF to my case. Concerning your questions:
1. Just try cell loop instead of face loop
2. No idea, maybe an UDF expert knows where a list with all available variables exists.
3. The UDF will be read every time step

Moritz

[sdarmayuda]

Hallo Moritz,

I see. Thank you very much for your help. I'll try to ask in Fluent UDF and Scheme Programming then.

Best regards,
Darma Yuda

[AlexanderZ]

Use ANSYS Fluent Customization Manual to find build-in macros (you call them variables) that are avaliable in fluent.

Instead of DEFINE_ADJUST function I'm suggesting you use DEFINE_PROFILE or even 2.3.41.DEFINE_TRANSIENT_PROFILE.

DEFINE_PROFILE is the common tool to modify boundary conditions in Fluent.

Best regards,

[sdarmayuda]

Hi AlexanderZ,

Thank you for your reply. I'm following your suggestion and change my UDF to DEFINE_TRANSIENT_PROFILE. But I still can't find the macro that let me use the calculated torque. I'm using Fluent 17.2 Academic. (I'm using the built in manual and this source https://www.sharcnet.ca/Software/Ans...f/flu_udf.html)

Can only the torque be calculated using the pressure*blade-area*arm? Here is my UDF.

******************************************
#include "udf.h"

DEFINE_TRANSIENT_PROFILE(testudf,CURRENT_TIME)
{
real omega_ts=0.0; /*starting omega*/
real omega_tf=600.0; /*final omega*/
real Jt=0.000554; /*Moment Inertia of the Turbin*/
real delta_t=0.0001; /*delta t simulation*/
real CURRENT_TIMESTEP;
real CURRENT_TIME;
real alpha_t; /*angular acceleration*/
Thread *t;
cell_t c;
t=Lookup_Thread(d,9); /*Zone ID = 9*/

begin_c_loop (c,t)
{
alpha_t= Mt/Jt; /*M = J*alpha, but how can I retrieve the value of Mt?*/
omega_ts+=alpha_t*CURRENT_TIMESTEP;

if (omega_ts > omega_tf)
{omega_ts = omega_tf;}

THREAD_VAR(t).fluid.omega=omega_ts;
}
end_c_loop (c,t)

}
************************************************** *

Thank you very much for your help. I'm really looking forward to your further reply.

Best regards,
Darma Yuda