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chandrasekhar.gullapalli January 11, 2011 08:36

New user for Fluent modeling -- help me
1 Attachment(s)
Problem is:
Attachment 6030
one circular face top of that, one trapezium face is there. Inclined edges of this trapezium are tangent to circle. As it is trapezium, edges will not touch circle at o or 270 degrees. They may touch at 285 and 350. So, how to create this type of face (Mix of trapezium and circle)

-mAx- January 12, 2011 02:13

1 Attachment(s)
You can create your face in 2 ways (also if you need a 3d geometry):
*with a cad sofware, then import in Gambit
*within Gambit
Attachment 6031

chandrasekhar.gullapalli January 12, 2011 02:43

How u r able to draw inclined line.

Thanks for the reply.. How u r able to draw inclined line...

If I am able to draw the exact line... then my problem will be solved. But, without knowing the angle, how it can be drawn...

-mAx- January 12, 2011 02:53

you can create a disk with diameter 1600. Place it at its right place according to your sketch.
Then if you well built the rectangle 1998x1158, you can use the vertex bottom left as center for a disk with radius 1166
Intercept the 2 disks, and you have the point defining your angle

chandrasekhar.gullapalli January 20, 2011 10:05

PA fan modeling
1 Attachment(s)
Hi Max,

I am able to. Now, one more problem araised..

Please find the attached. There are 2 views. It's outlet of fan.

Top portion iam able to. As it is hollow cubes... using boolean operations. I am to do..

But, bottom portion is hollow and surface profile is typical one...

can u please suggest, how to do model in Gambit...

I tried sweeping option, but iam not able to ...

If this task is over... Then I want to start modeling of blade profile...

Thanks & Regards,
chandrasekhar G.

Attachment 6148

-mAx- January 20, 2011 10:15

post a picture of what you already did, and repost your sketch with higher resolution (don't see anything)
and also a perspective view (if you have)

chandrasekhar.gullapalli January 21, 2011 00:52

Fan outlet modeling.
1 Attachment(s)
Attachment 6160

Hi Max,

The above drawing contains 2 views. This is outlet duct of fan. Top rectangualar section, which was considered as upper half can be modeled easily. It was done.

Now iam modeling lower half. it's a hollow one enclosed with surfaces of 8 mm thickness. With your help I did modeling for one side plate. remaining plates how to model. These are not simple in shape. I tried sweeping option. If i use sweep option, it will be not be hollow...

Please suggest the steps to model the lower half.

Thanks & Regards,
chandrasekhar G.

-mAx- January 21, 2011 02:29

Before going further, you have to ask you what do you want to compute?
If you say that your duct is hollow, it means your duct will be filled with your flow. So on the cfd side,your volume won't be hollow.
You need to mesh the fluid domain, not the solid.

chandrasekhar.gullapalli January 21, 2011 02:43

Analysis of air flow in side fan...
Hollow portion will be filled air. I agree. This need not to specify in continuum specifications. As it will be covered plates around it... And Inlet of fan, outlet of fan can be given as boundary conditions.

coming to meshing, I want to do meshing on inner surface of the plate and hollow portion. But, for the time being I don't know how to provide meshing.

Before that, I would like to model the profile as it is in the drawing. It helps for me to do simulation.

So, Please suggest me to do how to proceed further for modeling the hollow duct... Or is it the right approach...

-mAx- January 21, 2011 03:01

So you want your volume (extern surfaces designed following your drawings), but filled (not hollow), right?

chandrasekhar.gullapalli January 21, 2011 03:32

modeling & meshing...
Additions: I am going to add, Impeller in suction box. over that blades.

What u said is correct... modeling outer surfaces and provide meshing for the continuum (Here it is air). and face exposed to continuum. It may be inner surface of plates, blades, impeller hub and shaft...

So, please let me know how that type of profile to be modelled...

-mAx- January 21, 2011 03:42

ok, then from your front surface you can extrude it with a 1278 depth.
You can do that by sweeping your surface with the right vector. (you have now a volume)
Then you need to cut the lower and slant part.
From a lateral side, create the slant edge and small edge (detail X), and sweep those edges with 1998 depth.
Finally split your volume with the 2 surfaces, and delete the volume you don't need.
That's it
Be sure you have a real volume, and not a virtual (v_volume.xx), else you will have difficulties for substracting fans and other elements you will implement.

chandrasekhar.gullapalli January 21, 2011 05:04

:confused: Finally I am creating volume. :( It will look like a solid block...

It will not resemble actual physical representation, how fan looks like... outer casing made up of plates and inside impeller and blades can be viewed etc...:)

I think iam going in wrong track...

Please suggest the same...

If required i can forward my file... May I know what files do u need really... and the process...

-mAx- January 21, 2011 05:12

what do you want to calculate?
post a simply sketch with a box instead of your duct, your fan and expected streamlines
If you don't create a volume, then you have surface... and the only surface mesh you can compute is a planar one: for 2d

chandrasekhar.gullapalli January 21, 2011 05:59

PA fan simulation.
1 Attachment(s)
Attachment 6165

Hi attached.. is the fan model how iam making.. snap shot...

I want to see air pattern in side fan. when fan is rotating. and want to optimize the pressure drop.

Finally, i want to see simulation with impeller rotating along with blades over that air is moving... surrounding outer casing...

For example, if a hollow volume containing an obstruction attached to an innner surface, opened at opposite end... one is inlet and one is outlet.

How it can be modeled. After modeling Can I able to see inside obstruction over that how boundary layer is going to form...

Thanks for ur patience...

-mAx- January 21, 2011 06:19

You cannot do anything with your fan, since you only have outer surfaces.
Again: you need to mesh the fluid domain, eg: the volume where air is flowing.
With the mesh, you subdivide the fluid domain into small (very small) control volumes (or cells). And with CFD you will try to "solve" the NS equations on each cell.
So if you don't have fluid domain, then you don't have control volume (or cell), and you cannot compute anything.
Do a simple test: try to compute water flow in a 3d-pipe (straight one), with a massflow
Very very simple to model, mesh and compute.

chandrasekhar.gullapalli January 21, 2011 07:00

meshing and cut sections.
Thanks Max. The basic thing is clear. Yes u r right...

for meshing i need some thing... I can't create mesh inside air...

Type of mesh generally, how to select... Hexogonal, or triangualar. and near to boundaries how i can vary my mesh density.

or fluent it will take automatically the meshing... Can the surfaces be changed to glass type of look.

From where i can observe what is happening inside... or cutting sections...

-mAx- January 21, 2011 07:04

First create your computationnal domain (here volumes :) )

chandrasekhar.gullapalli January 27, 2011 04:55

Volume modeling for fan completed...
Hi max,

Modeling of volumes completed. There were 2 different types of volumes.

one is fluid volume, where fluid is continuum.

the other one is solid volume. This is the volume where fan blades, hub and shaft will come in the fluid domain, which i have to subtract.

Next step is : How to select grid type?

and one more querey?: Is there any option like offset in gambit?


-mAx- January 27, 2011 05:02

First substract your solid volumes from fluid domain
Then you have the definitiv volume fluid, and you can start meshing.
You can select grid type when you are in volume mesh panel.
But gambit will automatically choose one for you.
If your volume isn't "fit" for hexa, then you will have to subdivide your volume into logicals volumes, which could be hexa-meshable
I don't understand your last query

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