[vidysgr]

Hello,
I am new to this site because I always solve problems by myself. Unfortunately, for this sort of issue, I couldn't know how to approach it.

My question is As you see in the image I want to estimate the Cl and Cd graph.
After solving it the graph looks unusual.
Before this, I got the same results with an unmodified geometry that shows a warning with geometry issues in ANSYS.

Later I modified it in Solidworks and then I simulated it in ANSYS. I didn't see geometric errors. But the Cl and cd graphs and residuals convergence looks unusual. In fact, the solution is diverging.

As far as I know, I want to improve my meshing. But It's not possible. I tried different techniques to improve the mesh. But the mesh is not imroved is not generating in fact it shows a warning the couldn't be generated. So I stick to the default mesh with a bit more sizing as shown in the image.

Before the meshing, I saw a section plane that looks normal like a hallow inside. But after the meshing, it looks natural to me.

Considering my flight is flying at a low altitude ~2000 ft at speed of ~ 50 m/s. the density of air =1.154 kg/m^3
Initial gauge pressure is calculated with P =ρgh

For Post-processing: The Model is K-Epsilon.(considering K and E values in the boundary conditions for the velocity Inlet).
The pressure outlet I choose I didn't choose any value. (Is it correct or should choose the same as Initial gauge pressure)
What out K and Epsilon values in pressure outlet ?(Here it didn't choose the values are same where are k=1 and ε = 1) Is it correct?

The Area Choose is the Logitunidal section of the Aircraft instead of the Lateral section (Includes Wing area)
However it tried different possibilities by changing Aera, K, and ε however the results are the same.

Guys, I kindly request you to have a look at my problem and help with the solution.
Basically, I am using the 2015 version of ANSYS which I am comfortable with.
I have to evaluate this as soon as possible. and I will be waiting for your reply.

Sincerely,
Sagar

[LoGaL]

Your simulation is diverging, nothing unusual.
Either it's a bad mesh or wrong settings. I bet on the first one. What is your maximum skewness as reported by the ansys mesher?

[vidysgr]

Dear Lorenzo Galieti,
Thank you for responding immediately I this version I may not visible skewness that you can usually find in the 2019 version. The Orthonalaltiy is less as the software says.
As I mentioned I tried to improve mesh I Hexa dominant method with Free facing mesh type as all quad for an enclosure and tetrahedrons for the aircraft.
But the mesh is not possible.
(The related images are attached )
Is there any possible solution to this unimproved meshed file?. If it is In which way I should proceed?

Best wishes,
Sagar.

[LoGaL]

Dear Sagar,

No, if the mesh is really garbage (as it is), Fluent won't like it and you will get no solution. Or if you get something, it's as garbage as the mesh you provided. Period. You will spend more time trying to make Fluent work than the time you would spend to fix your mesh.

I can guarantee you from personal experience with the ansys mesher, that EVERYTHING can be meshed with a good quality mesh, provided you make the effort to do so. Some stuff take more time, some stuff take less

What you wrote here makes me feel that you opened the mesher, pushed some buttons and hoped it worked.

Originally Posted by vidysgr

As I mentioned I tried to improve mesh I Hexa dominant method with Free facing mesh type as all quad for an enclosure and tetrahedrons for the aircraft.
But the mesh is not possible.

However, since you are meshing a slightly complicated geometry, this clearly did not work. It's normal. Actually, in those cases, i.e. complicated geometry, easy physics, you spend a lot of time to generate a good quality mesh, then you open fluent, give basics settings, push the start button and it works flawlessly. I can guarantee also that.

What i suggest is to plot the skewness in the ansys mesher (NOT in fluent, in the mesher), to see where the bad quality cells are, so as to understand what is causing the problem. Then at that point it can be fixed.

In the ansys mesher, in the mesh options there's the possibility to select skewness in the "quality" part. Then it is also possible to set some ranges to display only the elements whose quality is in the range.

It could be that you simply need to set smaller elements in some regions of the domain, because the geometry is relatively small compared to the size of the aircraft ( I bet on the part below the aircraft, where there are all those beams)

It could also be that the CAD geometry is bad. In that case it has to be fixed in the CAD or in design modeler.

The problem is that if you don't spend time to understand what is generating a bad mesh, you wont solve your problem.