Hi,

The courant number is calculated from the formula v*dt/dx. So if you don't have movement of your fluid, it normal you have courant number equal to zero ( this is the consequence, not the cause). Your real problem is that you don't have any movement of you fluid.

Did you check you boundary and initial conditions? Do they really allow the movement of your fluid?

Yes sir i allow to move the wall as it is moving wall condition,with sinusoidal motion. I have attached udf. Can u plc check and highlight the mistake in this.

Thankyou

I never used Fluent and I'm not really an expert in C code. But taking a look at your, do you really specify to the software which coordinate of wall nodes you want to move? Which part does it?

What do you need Courant no.for? Fluent,Phoenics,etc use IMPLICIT schemes ,therefore they do not need Courant criterion.They are unconditionally stable.

Sir for transient condition i am giving velocity also so in that case during iteration, there should be some change in courant no. But in my case it coming fixed at zero

Are you using FLUENT? If so where do you ask the program to print Courant?

Courant will be computed if you use Fluent in its explicit or semi-implicit form.If you use it in its implicit mode it is zero simply because it is not computed.

Yes sir i m using fluent

R u implicit in time?

Dear

Is your case an unsteady one? Please make sure of this. Secondly time step size and minimum mesh size(Spatial axis) also matters. please check explicit or implicit schemes.

Regards

Taimur Ali Shams

I m doing in explicit scheme

So it should not be zero

Thats the problem i was facing

If u check your velocities and are not zero than it cannot be zero. Now do u compute it with your own programming?

If yes u obviously overwrite the velocities to zero.

yes sir i m doing it with my own programming

i m using sinusoidal udf.

i have attached it.

#include "udf.h"

# define A 0.05 /* AMPLITUDE = 0.05 m/s2 */

# define w 3.75 /* ANGULAR VELOCITY = 3.75 rad/s */

real AlnrX;

DEFINE_ADJUST(Accl,domain)

{

real t;

t = RP_Get_Real("flow-time");

AlnrX = A*sin(w*t); /* SINUSOIDAL MOTION */

printf("Time = %f\n",t);

printf("Acceleration = %f\n",AlnrX);

}

DEFINE_SOURCE(xmom_source,cell,thread,dS,eqn)

{

double pos[ND_ND];

double rho;

real source;

C_CENTROID(pos,cell,thread);

rho = C_R(cell,thread); /* DENSITY */

dS[eqn] = 0.0;

source = -AlnrX*rho; /* MOMENTUM SOURCE TERM */

return source;

}