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-   -   [ANSYS Meshing] Complete beginner :) - help/links needed! (http://www.cfd-online.com/Forums/ansys-meshing/97250-complete-beginner-help-links-needed.html)

Craig February 13, 2012 10:50

Complete beginner :) - help/links needed!
 
Hello. I'm completely new to this, and I'm trying to do some CFD analysis on an air intake from an aircraft. I've made a CAD model of the intake in Solid Edge, and I can export this in any format necessary. My main problem is that I have no idea how to create the mesh to go in CFX!

I've imported my CAD into Workbench, and then opened the Meshing tool but after that I can't understand where to go next - should I create a large box in the CAD file to act as an enclosure?

As I'm sure that I'm not the first person to be in this situation I was wondering if someone could point me in the direction of some tutorials/guides for complete beginners like me. There are way too many posts on here for me to search through, but hopefully somebody will have some good links.

Thank you!

PSYMN February 14, 2012 10:34

The tutorials are all up on the ANSYS customer portal... Check your license for your customer number which will allow you to create a login.

Even students with academic versions qualify...

I think there is also an academic portal now also, but I have not checked it out yet.

Craig February 21, 2012 06:02

Thanks PSYMN, but I can't currently access the portals (and hence the tutorials!).

I guess my current biggest problem is not knowing what the Meshing program expects of me. I've got a CAD model of the air intake, but do I need to have some sort of box around it? I don't know how the Meshing program knows how far away to make the mesh otherwise... or is it just making a mesh of the solid part? Do I otherwise need to make some sort of 'negative' CAD model, with a solid mould of the area that I'd like to mesh?

Thanks for your continued advice!

diamondx February 21, 2012 22:33

Ok, now you have your CAD model of the air intake. But that is not what your should be meshing. Yes, you need the box. What you need to do is actually create a big box and inside that box there is your air intake. pay attention when you create your box in ansys designmodeler, you need to specify the "add frozen" so the box won't merge with your geometry. After creating the box with that method , you will have two bodies. You need to do a boolean operation and delete the geometry of your air intake, WHY ?? Because the box represent the fluid moving and that is what you should be meshing, THE FLUID. and therefore your air intake will become like wall. Go to youtube and search for Analysis blunt body cfx and you will get a video about it. Let me know if you have more question. I'm a beginner too but i think i cleared that stage :D

mecbe2002 February 22, 2012 06:03

Hi,

Post your geometry, so that u ll get better answers.

From your post i guess ur trying to do internal aerodynamics of an intake, in that case u ve to mesh the interior domain.

Link to view the Ansys Fluent 12 tutorial guide http://my.fit.edu/itresources/manual...g/main_pre.htm

Do the first few tutorial to understand the CFD methodology and then try to solve proble. All the very best

Cheers
KGN

Craig February 24, 2012 13:10

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Thanks very much for your help guys - I think I'm slowly getting there! The youtube videos that diamondx mentioned were especially good - despite the terrible background music!

I've experienced a whole bunch of error messages (including lots about defeaturing) but I've managed to contain it to just 4 errors - have a look at the attached image for the screenshot. I've also included a picture of my geometry and a screenshot of my current mesh settings.

My problem now is that I'm just tweaking the mesh settings based on trial and error, and I'm not sure if I'll ever get something that finally makes the mesh :(! Interestingly, although it says that the mesh did not generate, it has a perfect wireframe model of the mesh, which even works when I take section planes...

Any further suggestions would be greatly appreciated! Thanks :)

diamondx February 24, 2012 13:15

You should be meshing that part ! you should be meshing the big rectangle. go back to ANSYS DESIGNMODELER and manke a boolean operation. target body is gonna the big rectangle and the tool body is gonna be your current geometry. then delete your geometry and keep only one body wish is the big rectangle and then mesh it. IF YOU DONT MIND SEND ME YOUR GEOMETRY TO TAKE A LOOK AT IT

Craig February 24, 2012 13:17

Hmm.. but if you look at http://www.youtube.com/watch?v=4wRCkh_qW3c then it suggests using an enclosure around the solid body is the way to go...

I'll try it your way now and see how I get on!

Craig February 25, 2012 06:50

diamondx - I tried it your way (by adding a box to my intake and using the boolean method, but it wouldn't mesh at all, no matter what I did to it. Using the enclosure technique as in the Youtube video I linked to above would at least display the mesh over the correct volume, even if it produced the errors in the screenshot I uploaded above.

Either way, I'm still no closer to doing any CFD analysis... :(

diamondx February 25, 2012 08:14

can you send me your geometry so i can take a look at it

diamondx February 27, 2012 16:36

I made a video on your geometry on how to export it to Ansys meshing . i divided by to because there is a symmetry. I hope it can help you :
http://www.youtube.com/watch?v=Bb8Tsd9eGe4

Craig February 28, 2012 12:55

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Thank you so much for taking the time to make a video - much appreciated! :D

Sadly however the problem still lies in the actual meshing procedure - if you'd let the meshing process run you'd have seen that it churns out various error messages depending on the minimum cell size chosen. The error messages seem to suggest increasing the cell size -but when I do this it simply fails due to a lack of detail.

It does mention using virtual topology, but I can't work out what that is or how to use it...

Anyway, I've attached a screenshot of the errors for what it's worth.

diamondx February 28, 2012 15:54

Sorry for not finishing the meshing process that was my bad. You were right. Something is going wrong with the meshing apparently because of your geometry. As i'm a beginner, my limits ends here, i tried using different method but it doesn't work. I hope somebody can hijack this thread and gives us a solution for it. Meanwhile, i look at some tutorials and lecture from the training material in Ansys meshing. I found a very interesting section talking about vitual topology and it might help you take a look at it it's easy to understand. start reading carefully from page 19. here is a link to the tutorial acccessible from my dropbox public folder.

http://dl.dropbox.com/u/35161486/AM-...ng_methods.pdf

diamondx February 28, 2012 17:24

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I'm back again, i analysed your geometry i found something wish is not good try to avoid this (see picture below)

Craig February 29, 2012 13:22

I noticed exactly the same thing - it's weird because it doesn't appear on my original CAD model (which I made in Solid Edge). Also, it doesn't appear on the opposite side, so I tried to get round the issue by halving the model on the other side to how you showed in the video, but that didn't work either... Pesky geometry!


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