Convergence per time step is fine. The simulation has run for more than 150 agitator revolutions. Residuals always bounce back at the begining of each new time step.

All the above sounds normal to me. A few thoughts.

Consider monitoring with USRTRN the velocities at several cells near the Rushton tubine but located in the stationary portion of the mix tank. Set the time step to give 3 to 5 degrees per step, so you can see how the movement of the blade impacts the local fluid velocities. Run for two or three full agitator rotations. Plot the data from USRTRN. If the solution is converged, you should see a repeating cyclical pattern in the velocities at the cells being monitored. There should be six cycles per revolution corresponding to the six paddles on the Rushton turbine.

If you restart from a dump file, be sure to read the grid from the dumpfile so the grid and solution field are matched.

Good Luck.

John

Hi Jan & John and other family members,

I have tried your suggestion of using quadratic time differencing; 15 and 30 iterations per time step, for 432 time steps. There is a modest convergence. I am running it again with more time steps.

John, I will try your suggestion of using USRTRN, however, I am not sure that I quite undertand your suggestion about the CYCLES PER REVOLUTION. Where do you specify this? What I have is just Z CYCLES PER REVOLUTION for the unmatched grid. My repeating geometry is a half tank so I set 2 cycles/rev. Provide more light please.

thanks

Nyatoto

If you are modeling half the geometry then 2 cycles per revolution is correct. But my previous comment was not referring the the cyclic connections. It was in reference to the flow field in the fixed portion of the vessel and how to determine if the model has reached a "stable" flow pattern. My comment was in response to your question on how may iterations did you need to run to get a converged solution. How about sharing your key learnings regarding convergence for your mixing tank model?

Thanks

Hi all,

I went for an overkill!! And I guess some people will disagree with my actions. Here is a summary of my systematic actions (done one at atime). -Refined the grids -doubled the default inner iterations -Used courant no of 5 and backward quadratic time scheme (as recommended by Jan, Thanks).

Then all the above set with.. -24,000 Total iterations!!! (that is NSTEP=600, MAXIT=40, DT=0.002sec, 60 impeller rev.)

Convergence seems better (It is still going on since Saturday 3.00pm, it is now 5.10 pm Monday).

As I had mentioned before, convergence is just one of the indicator of a good solution. I will inject my tracer and see what comes out now.

I will filter later some of the un necessary loads I have given my machine.

Many thanks John, Jan and KubaB. I will be back again with the tracer proper, after such a long suspension of the same.

regards nyatoto

[behruz]

hi all
i want to calculate mixing time in stirred vessel with tracer
i do not have any idea to do it.can any one help me?
thanks

[behruz]

hi all
i want to calculate mixing time with tracer.i do not have any idea to do it. can any one help me ? i need it extremly
thanks

[behruz]

hi
i am working in stirred tank . i want to calculate mixing time with tracer
i have not any idea to do it.can u help me?
i work with fluent.

[behruz]

hi all
i want to calculate mixing time in stirred vessel with tracer
i do not have any idea to do it.can any one help me?
thanks

[behruz]

hi all
i want to calculate mixing time in stirred vessel with tracer
i do not have any idea to do it.can any one help me?
thanks