Convergence problem

Clarence91 · September 12, 2014, 16:38

Thanks for reading this post.

My problem setup is 3D mesh with sliding mesh motion, transient flow,DPM.
After setting-up all the parameters and run the case, I am not able to get the convergence after few time-steps. Can anyone please help me?

BC for outlet is pressure-outlet. I even decreased the URF of momentum to 0.3 and discrete phase URF to 0.4.

Thnak you.

gfoam · September 16, 2014, 08:53

Hi, I don't understand very well the residuals you posted. First, it seems that you did a steady state simulation, after that you turn on the transient solver and after 900 iterations you get the residuals stabilized? Is that correct? The reasons for you to get divergence may be a lot, but first of all. What is the relative velocity in the sliding mesh, and what is the size of the domain and the relation between size/velocity and the time step are you using? Is it enough to get a good temporary discretization? What Courant number are you using? What schemes of spatial discretization? Well, for now let's check that, then we can see what else we can do. Regards
Gonzalo

Clarence91 · September 16, 2014, 12:08

For the first I switched-off DPM for the convergence and the rest is with DPM and everything is in transient flow.
I am using 2000RPM for the sliding mesh and the size of the geometry is (10.8*10.4*10.2)cm with inlet (0.6*10.2)
Timestep size is 0.0002, i think this is good for the discretization point of view. I am using a pressure-based solver with SIMPLE spatial discretization method.

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September 16, 2014, 08:53		#2
gfoam Senior Member Gonzalo Join Date: Mar 2011 Location: Argentina Posts: 122 Rep Power: 16	Hi, I don't understand very well the residuals you posted. First, it seems that you did a steady state simulation, after that you turn on the transient solver and after 900 iterations you get the residuals stabilized? Is that correct? The reasons for you to get divergence may be a lot, but first of all. What is the relative velocity in the sliding mesh, and what is the size of the domain and the relation between size/velocity and the time step are you using? Is it enough to get a good temporary discretization? What Courant number are you using? What schemes of spatial discretization? Well, for now let's check that, then we can see what else we can do. Regards Gonzalo

September 16, 2014, 12:08		#3
Clarence91 Member MarkClarence Join Date: Jul 2014 Posts: 32 Rep Power: 11	For the first I switched-off DPM for the convergence and the rest is with DPM and everything is in transient flow. I am using 2000RPM for the sliding mesh and the size of the geometry is (10.810.410.2)cm with inlet (0.6*10.2) Timestep size is 0.0002, i think this is good for the discretization point of view. I am using a pressure-based solver with SIMPLE spatial discretization method.