UDF for wall heat flux ?
 

Hi ! Fluent users

I am tring to use UDF to modificate the heat flux at the wall boundary. However, I can't find the Fluent's variable which denotes the wall heat flux in the function " DEFINE_HEAT_FLUX".

Is there anybody who know this variable name? please let me know.

Thanks in advance.

Re: UDF for wall heat flux ?
 

Looks like you may want to use DEFINE_PROFILE instead of DEFINE_HEAT_FLUX. DEFINE_PROFILE allows you to define a heat flux profile while DEFINE_HEAT_FLUX allows you to define the way to calculate heat flux. In other words, if you want to specify heat flux as a function of location, DEFINE_PROFILE is what you need.

Re: UDF for wall heat flux ?
 

"Looks like you may want to use DEFINE_PROFILE instead of DEFINE_HEAT_FLUX. DEFINE_PROFILE allows you to define a heat flux profile while DEFINE_HEAT_FLUX allows you to define the way to calculate heat flux.In other words, if you want to specify heat flux as a function of location, DEFINE_PROFILE is what you need."

Hi, I have a similar problem: I want to specify a heat transfer coeficients profile around a turbine blade in 3d. Ok, my profile is constant all over the blade span. To have an exemple of what FLUENT expects as an input file. I ran a dummy case, then PROFILE-> Write, I choose my surface and Heat transfer coefficient and now I have a file with: 4 vectors (x, y, z, heat transfer coefficients). I have a huge amount of points (all the nodes of my mesh I guess...), but I just want to specify a few points. Is there a mean of doing that or have I really to specify a value for each nodes???

Re: UDF for wall heat flux ?
 

My understanding is that

DEFINE_PROFILE allows you to define the heat flux profile at the surface

whereas

DEFINE_HEAT_FLUX allows you to define the heat transfer co-efficient profile at the surface

I have used both in my codes.

You can specify a constant or variable values depending upon how you write your udf. Do this by accessing the node, face data and adjacent cell data at the surface.

Example: If you want to modify just some points for a different heat transfer co-efficient you can use the example for DEFINE_HEAT_FLUX in the udf manual and add a test to change h at a particular region on the surface.

Greg

Hi
I am writing UDF code for variable heat flux over a circular tube but H value is unacceptable, could you please look at my UDF and tell me my mistakes?

#include "udf.h"
DEFINE_PROFILE(axial_flux_profile,t,i)
{
real x[ND_ND]; /* this will hold the position vector */
real q;
real m;
face_t f;

begin_f_loop(f,t)
{
F_CENTROID(x,f,t);
q = 0.5; /* q is the heat flux at z=0 in W/m2 */
m = 1;
F_PROFILE(f,t,i) = q*exp(0.5*m*x[3]);
}
end_f_loop(f,t)
}


Best Regards
Farzad:)

please help
how can i define the heat flux as a function of temperature of wall

q=1000*(1-0.014*(T-298))

any one can help me in writing the UDF please

x[3] is wrong I think. Because x dim = x[0], y = x[1] and z=x[2]