Boundaries explanation

Echidna · June 15, 2010, 13:42

Hello to everybody here.
This is my first post here and this is going to be a very easy question for all of you CFD experts. I am trying to analyse a competition car rear wing on Ansys CFX. I have designed the wing in CAD software. Then i must find a way to model a main boundary around this wing to model the air around of it.
Not knowing exactly how this is done in CFX, i also designed a large cube in CAD, i put the rear wing inside this large cube and then by means of "Boolean operations" i remove the volume of the wing out of the cube's volume. So i can make a decent analysis.
But i assume that there is some feature in CFX in which this is done automatically. The problem now is that i cannot take the walls of the rear wing and everytime the outer boundary (wall) is visible, confusing the things. I hope you can help me. Thanks!

Attesz · June 15, 2010, 15:06

So you want to turn on the wing visibility, and the outer walls not? In Mesh Regions there are all "Named" and Primitive faces, and you can turn them on separately. Is it your problem?

Echidna · June 15, 2010, 15:33

The real problem is that it seems wrong practise to me that you have to use Boolean operations in CAD to prepara the model and then analyse it.
To make it simpler:
Let's say you have a model for which you want to analyse its outer surfaces. For example an aircraft wing. Air is moving around the wing but not inside it.
You model the wing in CAD. Then you import the model in CFX. But, you need to have a large space aroung the wing which will simulate the space on which the wing is placed in reality, the open air.
So you need meshing onto this large space and on the outer surfaces of the wing. If you simply import the wing in CFX and you start meshing it, you will get mesh inside the wing's volume, something we don't want to occur.
So, my question is: How we set this large space (let's say the large boundary where thw flow is occuring) around the wing after we import the wing model in CFX?

Attesz · June 15, 2010, 16:03

Into CFX you can import only mesh.
The way is that you described, we have to cut out the solid bodies from the flow field's body. It is not simple?

in CAD you can do this also, or DesignModeller etc. You can create a cube, a cylinder, a half sphere, there are many ways depending on your case. You have to create the CAD model of the flow, because we want to simulate that.

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June 15, 2010, 15:06		#2
Attesz Senior Member Attesz Join Date: Mar 2009 Location: Munich Posts: 368 Rep Power: 17	So you want to turn on the wing visibility, and the outer walls not? In Mesh Regions there are all "Named" and Primitive faces, and you can turn them on separately. Is it your problem?

June 15, 2010, 15:33		#3
Echidna Member Join Date: Jun 2010 Posts: 77 Rep Power: 16	The real problem is that it seems wrong practise to me that you have to use Boolean operations in CAD to prepara the model and then analyse it. To make it simpler: Let's say you have a model for which you want to analyse its outer surfaces. For example an aircraft wing. Air is moving around the wing but not inside it. You model the wing in CAD. Then you import the model in CFX. But, you need to have a large space aroung the wing which will simulate the space on which the wing is placed in reality, the open air. So you need meshing onto this large space and on the outer surfaces of the wing. If you simply import the wing in CFX and you start meshing it, you will get mesh inside the wing's volume, something we don't want to occur. So, my question is: How we set this large space (let's say the large boundary where thw flow is occuring) around the wing after we import the wing model in CFX?

June 15, 2010, 16:03		#4
Attesz Senior Member Attesz Join Date: Mar 2009 Location: Munich Posts: 368 Rep Power: 17	Into CFX you can import only mesh. The way is that you described, we have to cut out the solid bodies from the flow field's body. It is not simple? in CAD you can do this also, or DesignModeller etc. You can create a cube, a cylinder, a half sphere, there are many ways depending on your case. You have to create the CAD model of the flow, because we want to simulate that.