Learning Forum

[bsmith643]

Hi, I'm relatively new to Fluent and I'm running a pretty simple flow analysis on a model. I'm looking at velocity and pressure drop for air flow through a heat exchanger. I haven't had any trouble meshing the model or setting up the analysis in Fluent, but when I start the calculation it never gets to the first iteration. I can see the background task running on my task manager but it never progresses. I have left it overnight before to see if it could make progress, but it was still on 0% and no iterations when I came in the next morning. The mesh has decent quality (0.2) and there are no errors when I run mesh checks or when I do the case check prior to beginning the calculation. I'm using hybrid initialization.

Any ideas where to start looking?

[Nikhil Narale]

Hello,

I would suggest you to try out following things:
1: Can you click on 'Check Case' button in the Run Calculation tab? Check what it has to say.
2: Can you try initializing using standard method and assign non-zero value to the flow variables?

Can you also tell,
1: What are the boundary conditions?
2: Are the material properties constant or defined as a function?

Nikhil

[Rob]

Can you post the panel you hit iterate on too.

[bsmith643]

Check case doesn't have any recommendations.
I haven't tried that.
Boundaries are 1 mass flow inlet with a fixed gas flow rate and a pressure outlet set to 0.
Using the standard Fluent "air" material.

[bsmith643]

Check case has no recommendations
This didn't work either
1 mass flow inlet with constant flow, 1 pressure outlet at gauge pressure
Using Ansys default air for fluid material. No solid geometry in the model.

[bsmith643]

Snip of the iterate screen.

[Rob]

Please post images in-line as staff aren't permitted to open attachments.

[bsmith643]

[Rob]

OK, that rules out the reporting interval clanger - ie you'd set the iterations in the update input and then nothing displays anywhere. With constant density you should use a velocity boundary for stability (won't alter the current issue). Does Mesh Check flag anything? How many cells have you got, and how much RAM?

[bsmith643]

Nothing from mesh check. Cell count is 35,933,399. RAM is 128GB

[Rob]

That should be OK but with only 8 cores it'll take a while to do the first iteration. How many monitors are there? Do you have 8 physical cores on the machine, if you're relying on hyperthreading it'll not end well.

[bsmith643]

I've left for about 14 hours before and it never completed the first iteration. Do you think it might take longer than that?
Computer has 12 cores on it.

[Rob]

No, I'd expect 10s of minutes. Even if the model then failed it should have reported something. I'd expect you be using around 90GB RAM too.