Learning Forum

[Kanak BUET19]

I am simulating the Selective Laser Melting (SLM) process in Ansys Fluent. I have designed the powder bed domain (along with the gas domain) with dimensions of 0.8 mm (x) x 0.2 mm (z) x 0.28 mm (y). During initialization, I patched the region with a height of 0.2 mm along the Y-axis as solid, and the rest as the gas domain, as shown in the image.

I need to apply a laser heat source at the interface of the solid-gas contact surface and also apply recoil pressure and Marangoni effect equations. I understand that a UDF is required for this. I found a UDF code from one of the posts in this forum (which does not include the Marangoni effect) which I have added at last part of the post. 

 

Here are my questions:

 

1. Material Properties Usage: If density and specific heat data are specified within the UDF, what is the use of the material properties defined in the "Materials" section inside Fluent? How does Fluent determine which properties to use during the simulation?

 

2. UDF Implementation Issue: I successfully compiled the code within ANSYS, hooked it under the Adjust section, and added the heat source term under the Cell Zone Boundary Condition. However, I don't see any changes in the results (i.e the phase shape does not change from the initial state) . I even defined 12 User-Defined Memory (UDM) locations. Can you help me identify what might have gone wrong?

 

UDF Code : 

 

 

 

#include "udf.h"

#include "sg_mphase.h"

#include "mem.h"

#include "sg_mem.h"

#include "math.h"

#include "flow.h"

#include "unsteady.h"

#include "metric.h"

 

#define A 0.4 // Absorption coefficient

#define P 200 // Laser power

#define R 80e-6 // Spot radius

#define v 0.1 // Scan speed of laser

#define h 25 // Heat transfer coefficient

#define Ta 300 // Ambient air temperature

#define s 5.67e-8 // Stefan Boltzmann constant

#define e 0.5 // Emissivity

#define Pi 3.1415926535

#define Ts 1658 // Solidus temperature

#define Tl 1723 // Liquidus temperature

#define x0 0.0// Initial x position of the laser

#define y0 0.1e-3 // Initial y position of the laser

#define Lv 7.45e6 // Latent heat of Vaporisation

#define Tv 3090 // Evaporation Temperature

#define Rg 8.314 // Universal Gas constant

#define M 0.005593 // Molar mass

#define Pa 101325 // Atmospheric pressure

#define domain_ID 3 // Domain ID of metal substrate

 

DEFINE_ADJUST(adjust_gradient, domain)

{

    Thread *t;

    Thread **pt;

    cell_t c;

    int phase_domain_index = 1.0;

    Domain *pDomain = DOMAIN_SUB_DOMAIN(domain,phase_domain_index);

    {

        Alloc_Storage_Vars(pDomain,SV_VOF_RG,SV_VOF_G,SV_NULL);

        Scalar_Reconstruction(pDomain, SV_VOF,-1,SV_VOF_RG,NULL);

        Scalar_Derivatives(pDomain,SV_VOF,-1,SV_VOF_G,SV_VOF_RG, Vof_Deriv_Accumulate);

    }

    mp_thread_loop_c(t,domain,pt)

    if (FLUID_THREAD_P(t))

    {

        Thread *ppt = pt[phase_domain_index];

        begin_c_loop (c,t)

        {

            C_UDMI(c,t,0) = C_VOF_G(c,ppt)[0];

            C_UDMI(c,t,1) = C_VOF_G(c,ppt)[1];

            C_UDMI(c,t,2) = C_VOF_G(c,ppt)[2];

            C_UDMI(c,t,3) = sqrt(C_UDMI(c,t,0)*C_UDMI(c,t,0) + C_UDMI(c,t,1)*C_UDMI(c,t,1) + C_UDMI(c,t,2)*C_UDMI(c,t,2));

        }

        end_c_loop (c,t)

    }

    Free_Storage_Vars(pDomain,SV_VOF_RG,SV_VOF_G,SV_NULL);

}

 

 

 

DEFINE_SOURCE(heat_source, c, t, dS, eqn)

{

    Thread *pri_th;

    Thread *sec_th;

    real source;

    real x[ND_ND], time;

    time = CURRENT_TIME;

    C_CENTROID(x, c, t);

    real T = C_T(c,t);

    

    pri_th = THREAD_SUB_THREAD(t, 0);

    sec_th = THREAD_SUB_THREAD(t, 1);

    

    real alpha = C_VOF(c,sec_th); // Use sub-thread for cell volume fraction

    real gamma = C_LIQF(c,sec_th); // Use sub-thread for cell liquid fraction

    

    real Pv = 0.54*Pa*exp((Lv*M*(T-Tv))/(Rg*T*Tv));

    real mv = (0.82*M*Pv)/(sqrt(2*Pi*M*Rg*T));

    real rhog = 1.6228; // Density of argon

    real rhos = 7900; // Density of solid SS316

    real rhol = 7433 + 0.0393*T - 0.00018*pow(T,2); // Density of liquid SS316

    real rhom = rhol*gamma + rhos*(1-gamma); // Density of SS316

    real rho = alpha*rhom + rhog*(1-alpha); // Density of cell containing metal and gas

    real Cpg = 520.64; // Specific heat of argon

    real Cps = 462 + 0.134*T; // Specific heat of solid SS316

    real Cpl = 775; // Specific heat of liquid SS316

    real Cpm = Cpl*gamma + Cps*(1-gamma); // Specific heat of SS316

    real Cp = alpha*Cpm + Cpg*(1-alpha); // Specific heat of cell containing metal and gas

    real factor = (2*rho*Cp)/(rhom*Cpm + rhog*Cpg);

 

    if(C_VOF(c,sec_th) > 0.05 && C_VOF(c,sec_th) < 1)

    {

        if(C_T(c,sec_th) < 3090)

        {

            source = (((2*A*P)/(Pi*R*R))*exp((-2*(pow(x[0]-x0-v*time,2.) + pow(x[1]-y0,2.)))/(R*R)) - h*(T-Ta) - s*e*(pow(T,4.) - pow(Ta,4.)))*C_UDMI(c,t,3)*factor;

            dS[eqn] = 0.0;

        }

        else if(C_T(c,sec_th) >= 3090)

        {

            source = (((2*A*P)/(Pi*R*R))*exp((-2*(pow(x[0]-x0-v*time,2.) + pow(x[1]-y0,2.)))/(R*R)) - h*(T-Ta) - s*e*(pow(T,4.) - pow(Ta,4.)) - Lv*mv)*C_UDMI(c,t,3)*factor;

            dS[eqn] = 0.0;

        }

    }

    else

    {

        source = 0.0;

        dS[eqn] = 0.0;

    }

    return source;

}

 

 

 

 

[Rob]

If you set material properties in the UDF as fixed values the code may use those if you tell it to. Or you can use the cell values which may make more sense. 

Looking at the code, it is a source term UDF. So, assuming you've hooked up the source term into the fluid volume, have you met the criteria for a heat source or is source=0 ?

[Kanak BUET19]

1. "Or you can use the cell values which may make more sense. " ------------ Can you tell me how exactly can I define in fluent to use the values within the code (and NOT the material data under the materials section? ) 
2. I am sorry I did not comprehend the question "have you met the criteria for a heat source or is source=0?" properly. I added this source term in the x-momentum source in cell zone boundary condtion. But I am not sure if this is correct , hear source ( whether they are surface or volumetric) should be inside ENERGY source right? 

I will really appreciate your suggestions on this problems sir . Thank you 

[Rob]

If you check the various examples you'll see Fluent has macros to call cell data, eg https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v242/en/flu_udf/flu_udf_DataAccessMacros.html  

You may have added the momentum source, but have the criterion of C_VOF and C_T been met to give a non zero value of source (heat_source)?