Stability problems with pressure as Bc

Altair Forum User

I have a concern regarding the stability of my simulation. I'm working with a snorkel air intake which suctions air from enviroment in order to feed the engine. I need to find the mass flow kg/s .

 

The geometry at inlet have some cells just like the snorkels for jeep , I have mesh this using a baffle approach and this part has a wall condition so fluid come in through this cells.

 

For that I have used at inlet pressure enviroment 101 325 Pa and outlet a negative pressure that represents vacuum (-33000 pa) flow must go from the snorkel (inlet) to the outlet which goes to the filter and after to the engine.

 

I'm using steady state simulation, spalart allmaras turbulence model.

 

I'm having non convergence and the value of the mass flow is super high which of course is non physical.

 

 

I would appreciate any comment or idea. I do think the problems are under Boundary conditions.

 

 

Thanks in advance.

ydigit

Please post your .inp and .Log files here. That would give more info, about the potential issues. Also a small sketch or screenshot of your setup would  be helpful.

Altair Forum User

Here is the files and  the image explain how this works , thanks!

<?xml version="1.0" encoding="UTF-8"?>

Unable to find an attachment - read this blog

Altair Forum User

Any suggestions?

ydigit

Apologies for the delay and thanks for the files.

There are two issues that were obvious from the .Log files. 

 

acuPrep: *** WARNING: Potential errors in boundary conditions: see file AEV_cfdmesh_setup_cp_v1.bc_warnings
acuPrep: ------------------------------------------------------------------
acuPrep:          Minimum coordinates = -7.9085e+002 6.2064e+002 3.8127e+002
acuPrep:          Maximum coordinates = 3.1172e+002 8.9606e+002 1.2587e+003

 

bc_warnings files needs to be checked and identify which nodes have warnings. If these are nodes between solids, it ok. If fluid nodes do not have a boundary condition, that needs to be rectified. 

 

Second issue is scaling. I guess you might have meshed in HyperMesh (from CAD data in mm). It needs to be scaled to 'Meters' to be best compatible with AcuConsole, as AcuConsole will write velocity,temperature,etc as Meter,Kg,Seconds, Kelvin.

In your case, the domain is -790m to 311m in X-Direction and so on. 

For such  a large case, #elements is clearly very less. 

 

Altair Forum User

Thanks how can I check dimensions (coordinates)  in my files? or in Acuconsole? in order to check if the dimensions are ok. I already fixed the issue of the BC warnings.

 

On the other hand how can I scale the mesh?

 

Many thanks!

ydigit

In acuConsole you can your MeshOp > Transform Coordinates to find or scale the dimensions. 

Another option, if you used HyperMesh to generate the mesh is to scale the mesh there, before export (Mesh > Scale).