[ANSYS Meshing] Meshing Element size

rizwan4081 · March 15, 2020, 16:56

Greetings.
I am new to Ansys Fluent. I am doing an analysis where I am analyzing the flow over a car in a tunnel. I have the Student version of the software with a limitation on the number of mesh elements of a max being 512000 cells. I would like to know how to calculate the minimum element size of the mesh?
The tunnel is 500 meters and by default the mesh element size is 25 meters, But I want to know if there is a way to calculate a minimum size so as to guarantee the convergence of solution?

fluidus · March 17, 2020, 14:28

Hi there,

I am no expert but some things come to mind:
-I think one of the key issues to reach convergence is to properly capture the boundary layer. How precisely do you want to capture it on the car surface? Depending on this you should set a minimum height to reach certain y+ values (https://www.cfd-online.com/Wiki/Dime...stance_(y_plus)). Ideally you should also capture it on the tunnel walls, but due to your limitation I think you should save some cells there.
-In my case it helps to divide your overall volume into smaller "boxes" and force the elements with Edge Sizing and increase the size as you get farther from the car.
-I don't know what mesher you are using. But if you are using Ansys Meshing you have some global parameters (under "Sizing") to play with. The ones I usually modify the most are the minimum size of element and face and the growth rate.

Finally, I think this reference would be really useful in your case: https://repository.lboro.ac.uk/artic...-0590_/9230000
It includes very detailed experimental data together with CAD model so you can validate your model.

I hope it helps.

March 15, 2020, 16:56	Meshing Element size	#1
rizwan4081 New Member Muhammad Rizwan Join Date: Mar 2020 Posts: 11 Rep Power: 6	Greetings. I am new to Ansys Fluent. I am doing an analysis where I am analyzing the flow over a car in a tunnel. I have the Student version of the software with a limitation on the number of mesh elements of a max being 512000 cells. I would like to know how to calculate the minimum element size of the mesh? The tunnel is 500 meters and by default the mesh element size is 25 meters, But I want to know if there is a way to calculate a minimum size so as to guarantee the convergence of solution?

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March 17, 2020, 14:28		#2
fluidus New Member Join Date: Dec 2019 Posts: 6 Rep Power: 6	Hi there, I am no expert but some things come to mind: -I think one of the key issues to reach convergence is to properly capture the boundary layer. How precisely do you want to capture it on the car surface? Depending on this you should set a minimum height to reach certain y+ values (https://www.cfd-online.com/Wiki/Dime...stance_(y_plus)). Ideally you should also capture it on the tunnel walls, but due to your limitation I think you should save some cells there. -In my case it helps to divide your overall volume into smaller "boxes" and force the elements with Edge Sizing and increase the size as you get farther from the car. -I don't know what mesher you are using. But if you are using Ansys Meshing you have some global parameters (under "Sizing") to play with. The ones I usually modify the most are the minimum size of element and face and the growth rate. Finally, I think this reference would be really useful in your case: https://repository.lboro.ac.uk/artic...-0590_/9230000 It includes very detailed experimental data together with CAD model so you can validate your model. I hope it helps.