Learning Forum

[Anthony Bowers]

Hello all,

I am trying to implement a custom advection-like term that occurs at a gas-liquid interface using User-Defined Scalara functions. See equation (1) 


To accomplish this term I am manipulating the DEFINE_UDS_FLUX term. See image below :

To implement this term using DEFINE_UDS_FLUX, the volume fraction gradient is obtained from a specific adjustment function where it is read by the DEFINE_UDS_FLUX. To make this term a flux, I linearly interpolate the volume fraction gradient values at neighboring cells to get a face value. See code below: 

DEFINE_UDS_FLUX(VolumFracGrad_Sink, f, t, i)

{

    cell_t c0, c1 = -1;

    Thread *t0, *t1 = NULL;

    real NV_VEC(A), flux = 0.0;

 

    // Cell pointers

    c0 = F_C0(f, t);

    t0 = F_C0_THREAD(f, t);

    c1 = F_C1(f, t);

    t1 = F_C1_THREAD(f, t);

    real grad_alpha[3];

    // Compute face area vector

    F_AREA(A, f, t);

    if (BOUNDARY_FACE_THREAD_P(t))

     {

            flux = 0;

     }

    else

    {

      // -------------------------------

    // 5. Gradient of alpha

    // -------------------------------

    grad_alpha[0] =(C_UDMI(c0, t0, 0)+C_UDMI(c1, t1, 0))*0.5;

    grad_alpha[1] =(C_UDMI(c0, t0, 1)+C_UDMI(c1, t1, 1))*0.5;

    grad_alpha[2] =(C_UDMI(c0, t0, 2)+C_UDMI(c1, t1, 2))*0.5;

    flux =  -NV_DOT(grad_alpha,A);

    }

 

    return flux;

}

However, when I run this code using a volume of fluid approach with a sharp interface and a highly refined domain, I obtain this result.

Has anyone came across a similar problem? I'd expect a uniform result, not a skewed result. If I just take the x-direction gradient with no face area attachted, I get this result :


It is very strange because If I plot the volume fraction gradient obtained in the defined adjust function (which is saved as C_UDMI(c,t,0 to 2) this is the results: 


However, it does seem that ansys is predicting a y-direction volume fraction gradient.. could this be the issue?