Bluff body problem


#1

Can someone explain why am I getting an error here
https://www.simscale.com/workbench/?pid=8142977915054623270#tab_1-0


#2

Hi @happy_gerrard,

can you just tell me of which simulation you are talking about?

Your bluff bodies remember me a bit of the so called Ahmed body. Is that what you are investigating at the moment?

You can have a look at a Project Spotlight I did a while ago: Ahmed Body

By importing the project you can see what has been done during the Pre-Processing & Post-Processing.

Feel free to add you questions/comments.

Cheers!


#3

Actually this is a bit different form ahmed body. Can you tell me why new-10-sp and10degsideplates are giving me an error. Some of the simulations are running just fine while others are showing an error even as the mesh and simulations are duplicates of the one which was error free.


#4

Hi @happy_gerrard, hope you are well. I had a look at your simulation and read the above comments. So I suspect from what you said, that this is caused by running out of memory. Although if I remember correctly you should get an error message saying this. If this is the case it is likely caused by your large meshes which are 17 and 34 million cells. So with this many cells, we need to be running on 32 cores, this is because the memory distribution also increases with a number of cores although I have forgotten how exactly it is distributed.

That said, I don’t think this level of refinement at the bluff body is required. I think I would be tempted to refine further the mesh region around the body and decrease it at the surface. This would increase the accuracy in the recirculation zone and have better results if you are looking at drag forces etc. I can see you are trying to fully resolve the boundary layer, so it might be better adding more layers instead of refining the surface that low. But this is my opinion, you know the problem your solving better than I do.

One more improvement that might improve stability is to add an initial velocity condition of -30m/s this means that there is no dramatic change when the simulation starts.

So in short if this is the issue one of these two will run without errors:

  1. Reduce mesh size
  2. Increase amount of Cores

If this doesn’t work then it isn’t a lack of memory. And we can investigate further :slight_smile:

Hope this helps you, any further issues just write back here
Darren


#5

Thanks, working out so far.


#6

Hi @happy_gerrard, glad it’s working out for you. I wanted to just say that I noticed that there was space between the bluff body and the symmetry edge of your mesh:

Not sure if this is intentional, but this would mean that there would theoretically be two bluff bodies separated by a thin channel.

Kind regards,
Darren


#7

It is intentional, although it would not mean two bluff bodies but a single one with a wide channel in the middle.