Learning Forum

[Fares]

Hello, everyone,

I am about to enter the boundary conditions for the simulation of a piston compressor. When I did the hybrid initialization, I get the following error message in fluent, that the convergence is not reached . i don't know exactly what the reason for this may be. Could you help me further?

[Karthik Remella]

Hi,nRegarding hybrid initialization - what is the mesh quality? This could be because of the poor mesh quality.nAre you applying 'Shared Topology' on your geometry? If you are willing to go through all these interfaces carefully, you can do that. If not, I'd strongly recommend performing 'Shared Topology'. on the geometry.nThanks.nKarthikn

[Fares]

Hi Karthik, nthank you very much for your feedback and help.nYeah, you're right.The mesh quality is not optimal because I use the student version: nI used an element size 2.1 mm for the fluids and 5 mm for the other bodies. Furthermore I created 3 layers per fluid.ni have for the global mesh a curvature of at least 1 mm and curvature normal angle 20°. nAn improvement of the mesh quality would be almost nimpossible, otherwise I would be over 512000 elements. nregarding the Share topology, I have used it but with the setting Automatic. Should I select the Imprints setting? nThanks!nFaresn

[Rob]

Try to remove some of the smaller features as that'll reduce the cell count (or allow you to use it more efficiently). If you've got contact regions where you don't expect them have a look to see what they are. The tool uses a tolerance algorithm which can be confused by smaller gaps between disconnected bodies that are small compared to the overall domain size. n

[Fares]

thank you very much for your support Rob. I checked the contact areas again and now I don't get the useless interfaces in fluent anymore. I have removed the screws to use the cells for refining the mesh in the fluid spaces.However, it still shows the message that the convergence is not achieved. nHow can I know how fine my mesh should be to achieve the convergence? or can the problem be due to something other than the mesh quality? nCan you please help me ?nThanks!nFaresnn

[Karthik Remella]

Can you please check your mesh quality - Max skewness should be less than 0.9 and Min orthogonal quality should be greater than 0.1. nBtw, have you tried running the simulation? Do you observe divergence?nThanks.nKarthikn