Hi Dear All,

I try to write a code for flows around circular cylinder. The basic parameters are

radius=6.8

IN=20 (inlet position from the cylinder)

NX=478 (must be larger than radius*50)
NY=71 (must be odd, must be larger than radius*2 I think).

Re=100 (Reynolds number)

t_max=500001 (Maximum time step)

ui=0.0666 (Inflow velocity:fixed within a low Mach number limit)

rho0=1.0 (Inflow density)

dt=dx=1 (lattice size and time step)

double nu = ui*2.0*radius/Re;

double tau_f = (6.0*nu+1.0)/2.0;
double re = ui*2.0*radius / nu;

int a = IN*(int)radius; // center of cylinder in x direction

int b = (NY-1)/2; // center of cylinder in y direction

Here i can also post the inlet/outlet and bounce back boundary conditions, may be i do some mistake here.

void bc_inlet()

{

int i,j;

i=0; // inlet bc

for(j=1;j<=NY-2;j++) {

f_1[i][j][1] = f_1[i+1][j][3] + 6.0*rho[i+1][j] w1ui;
f_1[i][j][5] = f_1[i+1][j+1][7] + 6.0*rho[i+1][j+1]

*w2*ui;

f_1[i][j][8] = f_1[i+1][j-1][6] + 6.0*rho[i+1][j-1]

*w2*ui;

}

}

void bc_outlet()

{

int i,j,k;

i=NX-1; // downstream bc

for(j=1;j<=NY-2;j++){

for(k=0;k<=8;k++){

// f_1[i][j][k] = 2.0*f_1[i-1][j][k] - f_1[i-2][j][k];

f_1[i][j][k] = f_1[i-1][j][k];

}

}

}

//bounce-back boundary condition for wall(channel) between 0 and 1 or between NY-2 and NY-1

void bc_bounceback()

{

int i;

for(i=0;i<=NX-2;i++){

f_1[i][0][5] = f_1[i+1][1][7];

f_1[i][NY-1][8] = f_1[i+1][NY-2][6];

}

for(i=1;i<=NX-2;i++){

f_1[i][0][2] = f_1[i][1][4];

f_1[i][NY-1][4] = f_1[i][NY-2][2];

}

for(i=2;i<=NX-1;i++){

f_1[i][0][6] = f_1[i-1][1][8];

f_1[i][NY-1][7] = f_1[i-1][NY-2][5];

}

}

For convergence test i used the L2-norm with the tolerance 1.0e-9

Inlet and outlet boundary conditions: Those proposed by Grunau et al.

Wall boundary condition: Symmetric and Bounce back boundary conditions

I have the following questions:

- Initially for 30000 time steps there is no lift coefficient and the convergence goes to 0.000001 and then increases again. I don’t know how many time steps is ok for this problem and why it happened.
- If i used the tolerance 5.0e-6 the convergence meet very quickly but i got no lift coefficients, don’t know why.

Can any one help me that the way i define all the parameters it’s ok or not. And why the shedding not happened for Reynolds number(=100) from initial also.

I need some help about such types of problems and if any one want to discuss about these problems and about my code then i can post the code on wiki also.

Thanks in advance

Khan