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-   -   [Other] Geometry and Meshing Questions (http://www.cfd-online.com/Forums/ansys-meshing/80548-geometry-meshing-questions.html)

Flaky September 29, 2010 09:00

Geometry and Meshing Questions
 
Hi all,

I am new to the ansys software.
At the moment i am suppose to model a fire tunnel with a heat source located at the center of the tunnel.

At the moment i have created a simple sample mode of 10x10x10 m fluid "enclosure" with a fire source of dimension 3x3x1m at the center of the enclosure.

I am i doubt regarding the geometry i have created as shown below.
Is the concept correct or should i remove the fire source geometry from the larger fluid enclosure to facilitate CFX simulation later.

Qns:
1) For CFD simulation, Hex element are usually preferred. Thus can i assume that the 2nd diagram would be the safer choice to proceed with?

http://i56.tinypic.com/vsjj8o.jpg
http://i56.tinypic.com/23kfebo.png

2) Is is possible to create a full hex mesh geometry of my above required description. Because the best i got was the diagram below. The mesh were unable to comform to each other when i try combining additional extrusion by both end along z and -z axis.

http://i53.tinypic.com/24111rk.png


Thanks in advance
I would appreciate comments and advice on improvement towards my geometry.

PSYMN October 1, 2010 22:19

Sweepable
 
Yes, it is possible to get a pure hexa mesh. You just need to chop your model into sweepable regions... There are tutorials that show how to do this.

Flaky October 4, 2010 08:04

Quote:

Originally Posted by PSYMN (Post 277474)
Yes, it is possible to get a pure hexa mesh. You just need to chop your model into sweepable regions... There are tutorials that show how to do this.

Thanks for your reply. I have since gotten some answers for my above questions. Have tired a pure hexa mesh vie sweep and edge sizing. Have attached a picture below.


http://i56.tinypic.com/255hq39.png
http://i56.tinypic.com/11uj03r.png


Dimensions base on 150m Length. Cross section 10m Wide 8m High.
Fire Source if 3mx3mx1m have been removed. Meshing is done on a split geometry for validation purpose later on.

Anyone with relevant expertise please kindly comment on my meshing if possible. Thanks in advance.

PSYMN October 5, 2010 18:00

Too Coarse
 
I would say it was much too coarse for CFD... but at least you got the sweep working...

Flaky October 5, 2010 21:47

Quote:

Originally Posted by PSYMN (Post 277976)
I would say it was much too coarse for CFD... but at least you got the sweep working...

Noted with thanks
Will try to work on the meshing.

Another question would be the geometry.
If i were to require a simple heat source to replace the "fire" in the tunnel,
do i have to model out a solid body so as to be able to set it as a domain and inserting a sub domain to input my heat release rate.

Because currently i am modeling the geometry with a void in the middle with the idea of setting the surface area around the void as a sub-domain for heat release rate. Is it possible to set the surface as a heat source without modeling a solid body?

Thanks in advance.

PSYMN October 7, 2010 12:44

Ask a Solver expert... But here is my 2 cents.
 
That sort of question is best asked on the solver threads.

Yes, you could just set a heat flux plus any radiation and temperature settings on that boundary. I guess you might need different settings for the sides front and top of the firebox...

Depending on your design, you may get a more accurate solution if actually modeled the firebox... For instance, the angle of the back walls inside an inset fireplace does affect the way that IR radiation (a key component in heat transfer from Fire) enters the room. If the angle is too steep, radiation just bounces back and forth within the box, but a shallower angle lets it radiate thru the opening and into the room. You have side an top surfaces to work with, so maybe you could take that sort of thing into account.

Flaky October 8, 2010 01:10

Quote:

Originally Posted by PSYMN (Post 278319)
That sort of question is best asked on the solver threads.

Yes, you could just set a heat flux plus any radiation and temperature settings on that boundary. I guess you might need different settings for the sides front and top of the firebox...

Depending on your design, you may get a more accurate solution if actually modeled the firebox... For instance, the angle of the back walls inside an inset fireplace does affect the way that IR radiation (a key component in heat transfer from Fire) enters the room. If the angle is too steep, radiation just bounces back and forth within the box, but a shallower angle lets it radiate thru the opening and into the room. You have side an top surfaces to work with, so maybe you could take that sort of thing into account.


Thanks a lot for your input and advice.
Much appreciated.


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