geometry and griding a stirred tank
 

I am trying to create a geometry of a stirred tank with rushton turbine in gambit to simulate in fluent, i have created the geometry through create volume option then i have united the volumes of the shaft, disc and blades to one volume and this volume is subtracted from the tank + baffle volume. I donot know what i have done is correct or incorrect i need to apply sliding mesh method in fluent but do not know how to grid the stirred tank.

this is my first post please somebody helpme. is there a tutorial available for geomerty, griding, mesh for stirred tank in gambit or elsewhere pls guide me.

You have to create 2 distinct zones: a zone surrounding the impeller (zone1) and the remaining one (zone2). If you want to use sliding mesh you have to create 3 interfaces between these 2 zones: one for vertical face(s) of zone1, one for the top face of zone1 and the last for the bottom face of zone1.
Zone1 will rotate, zone2 will remain static: proper sliding is ensured by interfaces.

Daniele

[Gambit] geometry and griding a stirred tank
 

Hi Daniele,

thank you for your reply.
When i create a volume near the impeller the volume of the tank get divide in two part while meshing the outer portion do i need to create more volumes such that the outer part is covered cant i mesh it directly.

Also since i have united the volumes of the Blade and disc. i am not able to mesh the common faces between the blade and the disc.

The sliding and the stationary zones and the interfaces have to define in Gambit or in Fluent

once again i thank you for your reply. Pls let me know if i am going wrong somewhere.

regards
meen

Hi!
I don't understand very well your questions.
I'm attaching a sketch of what you have to do.
Interfaces are defined in gambit in boundary conditions, then in fluent you have to couple interface1 with interface4, interface2 with interface5 and interface3 with interface6.
You can split more the volumes to control the mesh, but in zones definition, in gambit you have to set only 2 different zones, as represented in the picture.


Daniele

In complement to Daniele's advices, I add that your both volumes have to be disconnected.
copy and move trick always helped me (copy rotor volume anywhere, delete original volume . Enjoy this exotic rotor's placement for setting rotor interfaces (and also stator's ones). And finally move back. Now volumes are disconnected and interfaces are properly defined)

Q1: Is this necessary to create the sliding mesh interface (I do believe so). What will happen if we model this as single rotating reference frame similar to rotor with stationary casing?

Q2: Will there be any difference in results from both approaches?

Q3: How far interfaces should be placed?

@Daniele: Like this?

http://imageshack.us/a/img854/5774/stiringtank001.jpg

http://imageshack.us/a/img703/778/stiringtank005.jpg

http://imageshack.us/a/img834/2900/stiringtank004.jpg

http://imageshack.us/a/img819/3632/stiringtank006.jpg

http://imageshack.us/a/img27/6444/stiringtank003.jpg

When you have baffles or anything else which can interact with the fluid, sliding mesh is the most appropriate method; however, in certain cases, rotating reference frame can be a valid approximation (for example when you haven't baffles).

It depends: in general, sliding mesh approach will give the best approximation; as said before, if you have a simple tank with a central shaft/impeller, results should be similar.

This is the first question I tell to myself when approaching for the first time this type of problem: however, there's not a rule: simply your volume must contain the impeller.
Results should not change too much in respect of the size of the volume surrounding the impeller.

Yes, it seems correct to me.

Daniele

Can anyone please mail me the tutorials for drawing the geometry of stirred tank with baffles???

As I know, there is no specific gambit tutorial to draw an impeller/mixing tank.

Daniele

Thanks Daniel for your reply.
Can you just let me know the steps if you have worked on it...

Regards
Tarang

I usually work on autocad to build my geometries and then import them in gambit.
Just draw the vessel, (cylinder, cylinder+cone or whatever), then draw the impeller.
It's simpler to use some tools such as sweep, extrude, etc. (these are available in gambit too).
It's not simple to explain "how to draw" your geometry :)

Daniele

What will be the rotational speed of the zone 1? Will that be determined by the rotaional speed of the stirrer?
Will i have to use moving mesh for stirrer as well as zone 1?