Learning Forum

[awesomestudent]

Hello, I recently performed a simulation of Fluid Flow (Fluent). In the end, the calculation was made, at this residual chart was created. But I have no idea the meaning of it. Is good the chart? What is that fluctuating line? what causes it? Why some lines are straight? How do I fix/improve this? Any help would be much needed.

[Rob]

The residuals are a function of the error in the solution, and are one of the tools we use to judge if the solution is accurate. Have a look in the tutorials (click on Help) and other materials (click on Courses at the top of the page) for more information.
The plot you have suggests the solver is still trying to find a single converged state so may need to be run on for more iterations. However, you also need to check the mesh (cell quality and resolution) and set up to ensure it's suitable.

[awesomestudent]

I see, my cell quality is quite good. It has skewness below 0.98 and the resolution I used is 2. All are at high and fine meshing. I try performing on a higher number of iteration. Basically what I understand here is that the meshing greatly influence the residual chart.

[Rob]

A skew below 0.98 isn't good, below about 0.8 is good, under 0.95 is probably acceptable. Resolution of 2 just means you set a cell size: how does that compare to the geometry and flow field?

[awesomestudent]

This is the result of meshing

[Rob]

That just tells me the cells are all good. Plot a few contours of velocity & pressure with the node values off and post those.

[awesomestudent]

how do I do that? Do you have a link as guide?

[Rob]

Click on "Help" in Fluent and do the first few tutorials. All (should) become clear.

[awesomestudent]

I still don't know how and which HELP button to click

[Rob]

Any of them in Fluent - they all link to the documentation.