New user for Fluent modeling -- help me
 

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)

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

How u r able to draw inclined line.
 

Max,

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...

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

PA fan modeling
 

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

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)

Fan outlet modeling.
 

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.

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.

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...

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

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...

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.

: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...

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

PA fan simulation.
 

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...

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.

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...

First create your computationnal domain (here volumes :) )

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?

Chandu.

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

Offset of circles, lines, mesh...
 

Imagine a circle was drawn with 1m dia. In Autocad, if I use offset command and enter 0.2m value, I will get one more circle with 1.4m dia.

Is there any option like this,...

or one more example: a line was drawn at 70 deg angle to the horizontal. I need one more line parallel to the original at a distance of 8mm. And the second one also, to be in the same angle.

1. Mesh: Meshing I have to do for volumes, surfaces and edges or only volume is enough?

2. how to split volume into logical volumes?

3. I have two options, one is tetra hydral and hexogonal... Which is
better?

4. How to select sources for doing meshing? Anu specific criterion like selecting edges or surfaces?

Thanks in advance...

face/copy, there is an option "scale"
Your second example is just a copy with translation (edge/copy)
1. you can direct mesh the volume
2. by creating a surface, you can cut your volume with this surface (-->split)
3. you have more than 2 options:
*full tetra
*tetra hexcore (fill your domain with hexa in the core)
*hexa-map (outer surface with quad)
*hexa cooper (sources meshed with quad-pave)
etc...

You may decide what kind of mesh you want.
If you don't have time for very nice full hexa mesh, I would advice tetra-hexcore in combination with size fonction for local refining

Fan Simulation
 

Hi Max,

As I told earlier, I have 2 volumes.

1) Solid - Rotating part.

2) Fluid - Stationary part.

When I browsed through some threads, i saw: There should be sepearte mesh for below problem.

http://www.cfd-online.com/Forums/images/misc/tag.png http://www.cfd-online.com/Forums/ima.../paperclip.gif VAWT transient cfd problem

1) Whether I have to proceed in the same way?... As the interface between solid and fluid will change continuously....

2) Whether my problem will come as dynamic mesh...like in combustion engine.

3) What type of condition i have to give so that whole solid assembly should rotate at some rpm?

Please guide me...

They separate volumes for computing a sliding Mesh.
Rotor FLUID volume rotates since stator FLUID volume is stationnary.
The limit between the two domains is defined as Interface.
But you need to substract your fan.
1),2),3) --> don't jump so quickly in moving mesh.
Try first a steady one, and then go to moving mesh

Meshing for rotating frames
 

Hi Max,

after a long time. I had problem with meshing. I tried to solve example in Fluent 6.3 version tutorial - "multiple rotating reference frame models". And example outlined is "centrifugal fan-2d".

There are 3 fluid zones. Fluid one is outer casing, fluid -2 is blades portion (Which is rotating), fluid-3 is close to inlet or center. Please find the first figure for overall picture.

Attachment 6668

In the next figure, A closure snap was taken, where mesh nodes are same at interfaces for fluid zone.

Attachment 6671

Problem:

But, When I tried to model, for opposition rotation of blades. i.e. middle fluid volume containing blades mirror about vertical. and tried to do meshing. Now, I am getting different grid points at boundary.

Attachment 6672

One more thing: as middle fluid volume is rotating reference frame, the interfaces (Describled as wall in gambit) with other faces i have convert into interior type in fluent. there are 2 walls. Let's say wall-1 and wall-2.

I have to match grid points at the interfaces. As, when export it to fluent, it will create wall-1 shadow, and wall-2 shadow as these are seperated by fluid volumes.

But, if the above mismatch is happening shadow items are not created. inturn iam not able change boundary conditions in fluent from wall --> interior. I am not getting that option at all... I found this is due to meshing mismatch at interfaces of different fluid volumes.

May I know how to match.

your fluid zones don't have to match since your rotor will rotate.
In other words your rotor zone should be disconnected to other fluid zones.
After disconnecting you should be able to move your rotor zone without error (no link with other geometry)

Max,

My rotor zone is seperate only. My problem is with meshing...

Fig: 1: contains center mesh: 25 interval size, tri and pave mesh.

middle one: rotor portion: 50 interval size, tri and pave mesh.

outer one: 100 interval size, tri and pave mesh.

If you observe closely in Fig.2...

grid nodes of rotor fluid volume and outer volume are connecting at interface.

similarly for the rotor volume and inner volume.

But, where as in fig:3 (Reverse direction of rotation):

inner volume and rotor volume grid points are connecting. where as it is not for outer and rotor volume.

I want to mesh such away that the second case grid points also match at interface (i.e, outer and rotor volume). What procedure i have to follow to match the points... how to get that type of grid pattern...

hope this understands:

I don't understand:
you want disconnected zones, where meshes are matching together at interfaces?

Please see Fig:2: There are 3 different meshes. top one is: 100 interval size, inner one: 50...

mesh elements in rotor fluid are varying in size from outer (bigger) to inner (smaller).

similar case for inner fluid also.

Where as in fig:3, with same mesh specifications.

mesh elements in rotor volume are of equal size. but, inner one are vaying in size.

i would like to have mesh elements in varying in size for the rotor fluid also.

Hope this helps...

you want your rotor mesh having mesh gradient (from fine: inner to coarse: outer)?