Learning Forum

[mikeljapan]

I have just started using ANSYS FLUENT. If you have any knowledge, I hope you can help.

There are several tubes in a square space, and water vapor and hydrogen exist uniformly at an arbitrary volume fraction. A pressure boundary is set between the upper surface of the square space and inside the tubes. The thick part of the tubes is set as a porous zone, and only one substance (water-vapor or hydrogen) flows into the tube due to the viscous resistance of the porous. Multiphase flow model is used to set the porous viscous resistance for each substance. At present, material diffusion is not incorporated, so the UDS equation was set. However, the values of uds0 and uds1 are all 0 on the console screen of Fluent. Please tell me about this cause. Is nothing entered in Φk of the UDS equation with the current settings?

Here are the current settings.

Multiphase - Eulerian (Phase1 water-vapor, Phase2 hydrogen)

Energy - On

Viscous - Standard k-e

Radiation/Heat Exchanger/Species/Discrete phase/Acoustics/Eulerian Wall Film - Off

 

?uds-0    Inlet Diffusion - On

Phase - water-vapor (Phase1)

Solution Zones - all fluid zones, Flux Function - mass flow rate, Unsteady Function - default

 

?uds-1    Inlet Diffusion - On

Phase - hydrogen (Phase2)

Solution Zones - all fluid zones, Flux Function - mass flow rate, Unsteady Function - default

 

?Source Terms - Off (all cell zone)

 

?UDS Diffusion Coefficients

water-vapor - constant (e.g. 1.0e-5), hydrogen - constant (e.g. 1.0e-5)

 

?UDS Boundary Condition

Specific Flux - 0 (all boundary including inlet and outlet)←default settings

 

User Scalar 0 :0, User Scalar 1 :0

 

 

Thank you for reading to the end.

[Amine Ben Hadj Ali]

Why should uds now move? And why multiphase,?

[mikeljapan]

Does UDS not work with the current settings? I don't have an opinion to answer the question of why it move. It worked when set according to the user's guide, but all the values on the console screen became 0 like photo. Do I need to specify ?k? I didn't know how to do that after reading the manual.

Multiphase: I want to allow only water vapor to pass through the thick part of the tube and flow into the tube. For that purpose, the thick part of the tube was made porous. The multiphase was used only to set the viscous resistance of the porous material with vapor and hydrogen. Although it is a multiphase, both materials have gas values in their properties. Are there any alternatives to porous and multiphase?

Best regards mikeljapan

[Amine Ben Hadj Ali]

You are not providing diffusion and no convection so shall it change?
I do not understand your argument with multiphase as you can provide resistance too based on mass fraction via UDF.

[mikeljapan]

I want to provide diffusion and convection. What specific operations are required to provide diffusion and convection via UDS? Need to write program code? I think the diffusion coefficient will be given as a constant.

Best regards, 

mikeljapan

[Amine Ben Hadj Ali]

Share screenshot of UDS panel.

[Ramesh Chandra Mishra]

Hi

I have a problem after exporting UDF output to a text file. I am running simulation on a cluster and it runs well. I basically have 2 issues:
a)The value of UDS appears to be zero in the console for all the iterations. UDS is for the concentration of species which are emitted from a cell zone. Please note that the source is specifies in GUI and not the UDF. A snippet of my code is as follows:

DEFINE_ON_DEMAND(pch_udf)
{
FILE* fp_pch;
fp_pch = fopen("PCH.txt", "a");
Thread *t,*to, ;
face_t f;
cell_t co;
Domain *d;
d = Get_Domain(1);

real A[ND_ND];
real x[ND_ND];

real PCH_turb_roof=0;




//loop for turbulent component of PCH(Roof)
thread_loop_f(t, d)
{
begin_f_loop(f,t)
{
F_CENTROID(x, f, t);
if (x[0] >= 108 && x[0] <= 126 && x[1] == 18 && x[2] >= 90 && x[2] <= 126 )
{
F_AREA(A,f,t);
co = F_C0(f, t);
to = THREAD_T0(t);
real integrand;
real conc_grad_roof;
real mu_t_roof = C_MU_T(co,to);
C_UDSI(co,to,0)= C_YI(co,to,0) * RHO_1;
conc_grad_roof=(C_UDSI_G(co,to,0)[1]);
integrand = (mu_t_roof /0.7)*conc_grad_roof;
PCH_turb_roof -= integrand*NV_MAG(A);
}
}

end_f_loop(f,t)
}
fprintf(fp_pch, "PCH_turb_roof %g\n",PCH_turb_roof);
}

b) After complete simulations, the parameters defined under execute on demand are 0 for some iterations and non zero for some in the output text file. but it should be non-zero after every iteration as far as I understand. Please let me know if I am doing something wrong or interpreting them wrong. A snippet of the output file is as follows:

PCH_turb_roof 0
PCH_turb_side1 0
PCH_turb_side2 0
PCH_mean_roof 0
PCH_mean_side1 0
PCH_mean_side2 0
PCH_turb_roof 0
PCH_turb_side1 0
PCH_turb_side2 0
PCH_mean_roof 0
PCH_mean_side1 0
PCH_mean_side2 0
PCH_turb_roof 0
PCH_turb_side1 0
PCH_turb_side2 0
PCH_mean_roof 0
PCH_mean_side1 0
PCH_mean_side2 0
PCH_turb_roof 0
PCH_turb_side1 0
PCH_turb_side2 0
PCH_mean_roof 0
PCH_mean_side1 -4.6371
PCH_mean_side2 4.36109
PCH_turb_roof 0
PCH_turb_side1 0
PCH_turb_side2 0
PCH_mean_roof 0
PCH_mean_side1 0
PCH_mean_side2 0
PCH_turb_roof 0
PCH_turb_side1 0
PCH_turb_side2 0
PCH_mean_roof 0
PCH_mean_side1 0
PCH_mean_side2 0
PCH_turb_roof 0
PCH_turb_side1 0
PCH_turb_side2 0
PCH_mean_roof 0
PCH_mean_side1 0
PCH_mean_side2 -4.1951

 

Please note that other parameters visible in the text file have been specified in the code but not mentioned here.

Can you tell me how can i fix it?

[Rob]

Please don't post much the same question into many threads.