Learning Forum

[Deepak_296]

Dear, Experts!

I have simulated the trajectory of particles (10 microns each)in the 2D planar domain with a 2 mm bubble (spherical void) in it. Water is flowing from the inlet at a constant velocity. The velocity of the particle at the injection time is zero. I am able to see the particle trajectory after running the case, but it shows that few particles cross the spherical region which is not desirable. Particles should either slide on the spherical region or get attached to it. How can I achieve that?

[Rob]

Can you plot the flow velocity contour? Ideally with node values off.

[Deepak_296]

Thanks, Rob for your kind reply.
Please find flow velocity contour and velocity streamline with the particles.

[Rob]

I'm not sure the flow is converged and that's not with node values off: look in the Fluent contours panel for that.

[Deepak_296]

How can I check whether the flow has converged? Also, how can I check the time step convergence and mesh convergence?

[Rob]

Convergence is judged from the residuals, monitors and fluxes. If you're not sure about how, please click on Help in Fluent and review some of the tutorials.

[Deepak_296]

Thanks, Rob.
Residuals can be used to monitor the overall convergence of different parameters. Is 1e-3 is good convergence criteria for each residual? Also, how can I check the convergence for each time step for a given number of iterations?

[Deepak_296]

I have run the case for 5 timesteps for a given max number of iterations. Residuals are converging for each time step. I want to plot the residual for each variable separately. How can I plot it after running the case?

[Rob]

You can't unless you want to use the transcript file and do some work in Excel. You'll need a lot more than 5 time steps too to clear the initial conditions out of the model.

[Deepak_296]

Actually, I have to check my time step convergence. So, what would be a better way to check that? I considered only 5 time steps which are not good as you pointed out. What would be an ideal number of time steps depending to confirm the time step convergence?

[Rob]

You need all time steps to converge, and run enough to complete the simulation. To check for time step convergence plot the number of iterations used, I think there's a default report for that.

[Deepak_296]

While using the DPM model, how can I ensure that it is one-way coupling so that phase flow is not affected by the particles but the particles' motion is affected? I am trying to simulate the flow of water around a spherical void in a 2D planar domain, but the phase flow itself is getting affected by the particles. This can be seen in one of the pictures. I am unable to fix that.

[Rob]

One way coupling is automatic, two way needs the "interact with continuous phase" turned on.

[Deepak_296]

Will the streamline of phase flow be the same as without the injection of particles? Because I can see that it gets changed on injection of particles as shown in the previous figure. I am confused now.

[Rob]

The particles will not alter the streamlines if the DPM isn't coupled. However, if the solution is transient or poorly converged the streamlines will change between iterations.

[Deepak_296]

My solution is transient. So, is it desirable for the streamline to get altered?

[Rob]

Streamlines are a way of showing the flow patterns: if the flow changes then I'd expect the streamlines to change.