droplet bagmode breakup under hight density ratio .

[张祥]

Dear all,

I am a student want to simulate 2 dimension droplet bagmode breakup under high density ratio. and now I have completed low density ration simulation .such as rhol/rhog = 80

But when i use high density ratio,such as rhol/rhog = 100/1.2,mu suface become unstable . what should I do to solve this problem ? I guess this is because the momentum unconserved .But I dont know how to solve .

and my total program is below 

#define dimension 2

#include "axi.h"

#include "navier-stokes/centered.h"

#include "two-phase.h"

#include "navier-stokes/conserving.h"

#include "tension.h"

#include "view.h"

// ============para===================

#define RHOL 800.

#define MUL 50.e-3

#define SIGMA 0.03

/**Air properties*/

#define RHOG 10.

#define MUG 1.e-3

/**Drop diameter and stream velocity*/

#define DIAMETER 6.7e-3

#define USTREAM 3.

int minlevel = 6;  

int MAXLEVEL = 9;  

double maxruntime = HUGE;

u.n[left]  = dirichlet(USTREAM);

u.t[left]  = dirichlet(0);

p[left]    = neumann(0);

u.n[right] = neumann(0);

p[right]   = dirichlet(0);

// =========================================

int main (int argc, char * argv[]) {

  L0 = 10*DIAMETER;

  X0 = 0.;

  Y0 = 0.;

  // nondimensional para

  double Re = RHOG * USTREAM * DIAMETER / MUG;

  double We = RHOG * USTREAM * USTREAM * DIAMETER / SIGMA;

  double Oh = MUL / sqrt(RHOL * SIGMA * DIAMETER);

  double rho_ratio = RHOL / RHOG;

  double mu_ratio  = MUL / MUG;

  fprintf(stderr, "\n==== Dimensionless Numbers ====\n");

  fprintf(stderr, "Reynolds number (Re):       %.2f\n", Re);

  fprintf(stderr, "Weber number (We):          %.2f\n", We);

  fprintf(stderr, "Ohnesorge number (Oh):      %.4f\n", Oh);

  fprintf(stderr, "Density ratio (rho_l/rho_g): %.2f\n", rho_ratio);

  fprintf(stderr, "Viscosity ratio (mu_l/mu_g): %.2f\n", mu_ratio);

  fprintf(stderr, "===============================\n\n");

 

  double minDelta = L0/pow(2.0,MAXLEVEL);

  double sigmaTSLimit = sqrt(min(RHOL, RHOG)*pow(minDelta,3.0)/(SIGMA));

  double muTSLimit = min(MUL, MUG)*minDelta/SIGMA;

  DT = min(sigmaTSLimit,muTSLimit);

  CFL = 0.4;

  f.sigma = SIGMA;

  rho1 = RHOL;

  rho2 = RHOG;

  mu1 = MUL;

  mu2 = MUG;

  TOLERANCE = 1e-4;

  run();

 

}

event init (t = 0) {

  refine (sq(x-2*DIAMETER) + sq(y) - sq(0.6*DIAMETER) < 0 && sq(x - 2*DIAMETER) + sq(y) - sq(0.4*DIAMETER) > 0 && level < MAXLEVEL);

  fraction (f, sq(0.5*DIAMETER) - (sq(x - 2*DIAMETER) + sq(y)));

}

event adapt (i++) {

  double uemax = 5e-2;

  adapt_wavelet ({f,u}, (double[]){1e-3,uemax,uemax,uemax}, MAXLEVEL, minlevel);

}

event end (t= 0.06) {

}

//==================log=================

event logfile (i += 100 ,first) {

  if (i == 0){

    fprintf (ferr,

       "t dt mgp.i mgpf.i mgu.i perf.t perf.speed grid->tn\n");

  }

  fprintf (ferr,

     "%g %g %d %d %d"

     "%.2e %.2e %ld \n",

     t, dt, mgp.i, mgpf.i, mgu.i,

     perf.t, perf.speed, grid->tn);

  fflush (ferr);

}

//===================ppm=========================

//====================================

int frame = 0;

event movies ( t += 1.e-3 )

{

  view (fov = 12, width = 1920, height = 1080,tx = -0.6 , ty = -0.2);

  clear();

  draw_vof ("f", filled = 1, lw = 1, lc = {1, 1, 1}, fc = {0.6, 0.8, 1.0});

  cells();

  char name[256];

 

  sprintf(name, "ppm/snapshot-%d.ppm", frame++);

  save(name);

}

//===================field=========================

//====================================

// int num2 = 0;

// event output_slice (t += 1.e-3) {

//   char name[80];

//   sprintf(name, "field/%d.csv", num2++);  

//   FILE * fp = fopen(name, "w");

//   fprintf(fp, "x,y,f,u_x,u_y,p\n");

//   foreach() {

//     fprintf(fp, "%g,%g,%g,%g,%g,%g\n",

//             x, y, f[], u.x[], u.y[], p[]);

//   }

//   fclose(fp);

// }

//===================dump=================

//====================================

// event dumps ( t += 1.e-2) {

//   char fn[99];

//   sprintf (fn, "dump/dump-%g", t);

//   dump (file = fn);  // 储存当前网格、变量等

// }

[David Tang]

Hello Xiang,

If you're still having trouble with the aerobreakup code, could you possibly try increasing the maximum grid resolution level first? Some of the spurious behaviour of the droplet surface would go away at higher grid resolution levels.

Best,

David