[RodriguezFatz]

Residuals seem to be too high, but one can never just judge that from the numbers. Normally they should reduce to very low numbers. Did you try to run with just 1st order schemes?

[gustavosimiema]

No.. just second orders. Do you think it will be a good idea to start with first order and small values of mass flow. And after some convergence change to second order and increasing slowly the mass flow?

[RodriguezFatz]

These are two different things.
1) "Small flow": use it to get rid of the temperature divergence.
2) "1st order": use it to see if the high residuals are a numerical / mesh problem.

[gustavosimiema]

OK ..

2) If the residuals are still high with 1st order. Then I can conclude that I have a numerical problem or meshing problem? If it´s numerical what are the adjustments possible to be done? If it´s meshing, the adjustments should be change from unstructured to structured? Or maybe do more refinements?


An additional question:
To measure the mass flow in each hole I need to create a surface plane in each hole? There isn´t a easier way?

[RodriguezFatz]

2) There might be many reasons for high residuals... you say the flow is laminar, is this true at every region of your domain? The mesh could be too coarse, the solver not good...

I would create surfaces inside your domain in the design modeler and create named selections. Then in fluent, they will be treated as inner surfaces.

[gustavosimiema]

Very nice idea.

I will try everything we discussed today. Next week I´ll let you know what I obtained.

Thank you so much

[RodriguezFatz]

I don't recall that very good, but I think you have to have more than one fluid domain to get "inner" surfaces in the design modeler. So you might need to use "frozen" bodies in DM and join them via the "group". Then, you can select the inner connections as named selections.

[gustavosimiema]

My model I did at Inventor without assembly. Actually I modelled the negative so it is the fluid domain. As far as I could understand, this way I have done doesn´t allows me to create this inner surface. So I should create my model in different parts? Because one thing I don´t know (that´s why I have done the negative in one model) is because in my case is like I have One body inside the other (pipe inside the chamber). So with this configuration I could not create the fluid volume using the Fill concept in Design Modeller. Did I do something wrong? Do you have a better alternative? I did the negative in order to avoid using Fill concept...

[gustavosimiema]

So, increasing slowly the mass flow rate I solved the temperature problem. But the continuity residuals is constant but in a high value. Please, take a look in the attachment.
The mass flux report is as follow:

Mass Flow Rate (kg/s)
-------------------------------- --------------------
inlet 1.1438803e-05
outlet -1.1438793e-05
---------------- --------------------
Net 1.0004442e-11

What´s your opinion?

[RodriguezFatz]

That doesn't look good. Residuals are too high. What numerical settings do you use?

[gustavosimiema]

I used, SIMPLE, first order for all... and Pressure - Standard...
I have no idea what to do in order to improve it...

[gustavosimiema]

Maybe try something with under relaxation factor? I ran with default... maybe to decrease density factor or momentum factor... What do you think?

[RodriguezFatz]

I don't think this is the problem. I guess it is the mesh.
Did you improve the mesh from the pictures?
Could you post some pictures of the mesh? Maybe also some cuts through important regions to see some inner parts of the mesh?

[gustavosimiema]

Yes. I think I improved. At least looks better. I also simplified the model. I removed the curves in order to save calculation time.

Please find in attach the images.
1) Is the Cad model
2)Mesh
3)Mesh section

What´s your opinion?

[RodriguezFatz]

Ok, did you calculate Re in the pipes?
This is mass-flow inlet and pressure outlet, right?

[gustavosimiema]

Yes I calculated the Re... the highest was in the inlet ~90..
I attached some countours images.. Maybe can clarify something.

You are correct, I used mass flow inlet and pressure outlet.
What do you think?

[RodriguezFatz]

Hard to figure out from here... I would make the grid much finer and just see if residuals become smaller. If you can (numerically) afford that...

[gustavosimiema]

I also found this inofmration in the manual: (http://aerojet.engr.ucdavis.edu/flue...g/node1067.htm)

"Sometimes, however, this criterion may not be appropriate. Typical situations are listed below.

If you make a good initial guess of the flow field, the initial continuity residual may be very small leading to a large scaled residual for the continuity equation. In such a situation it is useful to examine the unscaled residual and compare it with an appropriate scale, such as the mass flow rate at the inlet."


Could my situation be this case?

[RodriguezFatz]

I don't run laminar cases, maybe this is ok...

[gustavosimiema]

Because I´m having problems just with the continuity residuals, the others are lower enough.

And the mass flux report shows imbalance less than 1%...

Mass Flow Rate (kg/s)
-------------------------------- --------------------
inlet 1.1438803e-05
outlet -1.1438793e-05
---------------- --------------------
Net 1.0004442e-11