Autodesk cfd troubles

[kasper.keating]

Hello there, I have a few unexplained problems when using autodesk cfd. 

• First of all, is there a more reliable way to see the no. elements in the simulation? It estimates 1.1 million but it’s actually 31+ million. 
• Also is there any way to tell approximately how long the simulation will take to complete? 
• I’m also having trouble with many simulations not being stable and crashing at one point or another and files going completely corrupt. I would understand the crashing if it had to do with ram yet I have 80gb of ram. The issue I’ve been having recently is running the simulation, then when the simulation completes the whole application closes, upon reopening the file, the results are not visible, so then I redo 0 iterations from the Nth iteration and the same thing happens but this time the file no longer opens. 
• Also, how come i always see errors on both surfaces and edges in the diagnostics tool, there’s no explanation of why or what is causing the errors, they’re still there after using the edge merge and small object tool.
• One final question, for a system of pipes submerged in a vat filled with fluid, would 15 wall layers be beneficial? I’m struggling because the simulations are taking 24 hours and then won’t even display the results.

Any and all help would be much appreciated!

[karol.suchon · Accepted solution]

Hello Kasper,

• the only reliable way to get the number of elements is by creating the mesh before the simulation. The approximation does not take into account the wall layers which could blow up the number of the mesh.
• Before we start the simulation we are not able to determine the amount of time necessary to finish the simulation. But if you measure the time between the 1 and 2 iterations, you should get the time for 1 iteration and we multiply the value by the number of iterations left. More or less we shopuld get the time of the simulation. Of course, the simulation could converge earlier etc.
• there could be a problem with rendering one of the results features like plane etc. Please check the solution from an article in that simulation.
• You could have a not clean enough model, even if the software merges or delete small surfaces, object there could still be a lot of problems with the mesh creation. You could try to use a diagnostic tool and refine the problematic surfaces, but from my experience, it is always better to back to CAD software and clean or simplified it. Refining the surface to the moment when we do not get the mesh could give a few million additional mesh elements in a place where rather not be interested to get results.

• The wall layers should be directly connected to the turbulence model and Y+ parameter. Please check the webinar, it should give you more overall info about it. From the information you provided, I am not able to tell if that is enough or not 🙂

BR
Karol

[kasper.keating]

Excellent, thank you very much!