[Sorabh]

Hello, I am solving a 2D-axisymmetrical laser heating problem.



The laser radius is 0.4mm and it has a profile I = I0*exp(-del*x), where x is the x co-ordinate of the cell and del is the absorptivity coefficient in m^-1 . I wrote the following macro for heat source:

DEFINE_SOURCE(top_hat,c,t,dS,eqn)
{
    real x[ND_ND],time;
    real x0,y0,source;
        real I0 = 1e5;
        real del = 1;
    time=RP_Get_Real("flow-time");
    C_CENTROID(x,c,t);
    x0 = x[0];
    y0 = x[1];
    if (y0 > 0 && y0 < 0.4e-3)
    {
        source = I0*exp(-del*x);
        dS[eqn] = 0;
    }    
    else
    {
        source = 0;
        dS[eqn] = 0;
    }
    
    return source;
}

However results are not what is expected. I expected a parabolic profile of temperature, but I get the following.



Is the source term macro correctly defined?

Thanks

[gearboy]

Originally Posted by Sorabh

Hello, I am solving a 2D-axisymmetrical laser heating problem.



The laser radius is 0.4mm and it has a profile I = I0*exp(-del*x), where x is the x co-ordinate of the cell and del is the absorptivity coefficient in m^-1 . I wrote the following macro for heat source:

DEFINE_SOURCE(top_hat,c,t,dS,eqn)
{
    real x[ND_ND],time;
    real x0,y0,source;
        real I0 = 1e5;
        real del = 1;
    time=RP_Get_Real("flow-time");
    C_CENTROID(x,c,t);
    x0 = x[0];
    y0 = x[1];
    if (y0 > 0 && y0 < 0.4e-3)
    {
        source = I0*exp(-del*x);
        dS[eqn] = 0;
    }    
    else
    {
        source = 0;
        dS[eqn] = 0;
    }
    
    return source;
}

However results are not what is expected. I expected a parabolic profile of temperature, but I get the following.



Is the source term macro correctly defined?

Thanks

DEFINE_SOURCE will apply to all cells in the domain. So your condition y0 > 0 && y0 < 0.4e-3 will apply to all the cells whose y coordinate <0.4e-3.
You should add additional condition to specify only the first column cells near the left wall. Or another method, do not use DEFINE_SOURCE, just use DEFINE_PROFILE to specify the heat flux on left wall.

[Sorabh]

Originally Posted by gearboy

DEFINE_SOURCE will apply to all cells in the domain. So your condition y0 > 0 && y0 < 0.4e-3 will apply to all the cells whose y coordinate <0.4e-3.
You should add additional condition to specify only the first column cells near the left wall. Or another method, do not use DEFINE_SOURCE, just use DEFINE_PROFILE to specify the heat flux on left wall.

Thanks... but I have defined a condition 'I = I0*exp(-alpha*x)' where alpha = 1.
Will that not be enough to constraint along x axis?
I also considered using the DEFINE_PROFILE to specify heat flux on the wall.. but it is supposed to be a volumetric heat source, hence both x and y (not just y) co-ordinates should be involved.

[obscureed]

Hi Sorabh,

Here are a few thoughts:


++ It is a mistake to write "exp(-del*x)", since x is an array. A helpful compiler would have issued a warning about this. Instead, try "exp(-del*x0)".


++ If you make this correction, the source looks correctly defined. The test for "if(y>0)" is pointless (since y<0, and on this occasion even y==0 are impossible).

++ I do not remember the details of source terms in 2D-axisymmetric simulations, but I do remember that you need to check the details. Is the source really "per m3", or is it in fact "per angle of rotation" (hence missing a factor of 2*M_PI)? You need to check this -- and I would not trust my understanding of the manuals (and I would not assume that UDFs and GUI-defined values use the same rules), so you need to check this in a test model. I cannot stress this too much. If you do not do this check, you should regard your results as doubtful to within a factor of 2*M_PI.


++ If your model's extent in the x-direction is small compared to the lengthscale "(1./del)", then the rate of source will be approximately constant in the x-direction. In that sense, I do not see your results as obviously wrong.

Good luck!
Ed

[Sorabh]

Yeah, I did what you said.. the 'x' in the equation was actually x[0], and the heat generation is defined in W/m^3, so that is sorted out.

I noticed that whenever the point of heat generation is at one of the boundaries, the solution is borked.. but it works when the heat is generated 'within' the doman...