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luai May 18, 2012 20:23

aerator simulation with CFX
hi all...
i'm trying to solve this problem with CFX5, but till now i failed due to wrong configurations, hope you can help me with these one,and i w'll be so greatful.
my problem explain how aerator works in sludge lagoon in waste water treatment plans, the aerator rotate at 43 rpm and i already made symmetry plans,but the main problem i had is what the boundary that i should add, the interfaces too, and why i can't run the problem with turbo mode?
the purpose for this problem is to simulate how water get in and out throught the aerator. and to know the dead point.



ghorrocks May 19, 2012 07:25

Can you show an drawing or photograph of what you want to model?

luai May 19, 2012 08:18

the surface aerator schemes
this may help!
surface aerator drawing:

surface aerator work flow:

picture for aerator (the blades here is different from my model, but with the same working idea)

surface aerator (solidworks part):

thanks ghorrocks,


ghorrocks May 20, 2012 07:18

Thank you for the very clear description. I understand what you are trying to do now - few people bother putting clear descriptions in their posts.

First of all, a comment which will make a major difference to run time:
Your geometry appears to have 15 or 20 blades. So rather than model a 90° segment with 5 or so blades, model 1/n of it, where n is the number of blades - that is a single blade passage. Use periodic interfaces on either sides. Providing the flow is the same in all passages this approach will save a lot of time and difficulty.

A second comment which also simplifies things:
You do not need a stationary and rotating part in the model I see you have above. Just put the thing in one big rotating domain. Then you do not need interfaces and that simplifies things.

There are a few approaches you can take with this. Rather than the inlet flow rate you have specified, why not just put the device in liquid and let it generate its own flow? That is what the thing does in real life.

luai May 21, 2012 07:21

some comments
Thanks a lot for your car ghorrocks,
I got the main idea that you provided, but I’m not sure if i can do it right without your help!!!
This is the modified 3D aerator with one blade and two passages. I put some boundaries on it but not sure if its right!?

Where i must put periodic interfaces, (in the both sides of the water domain!?)
i make two domain, have the same fluid (water), and both are rotating at 47 rpm, but i fail to show the total blades in CFD-POST, because the main goal of the simulation is to show the water how get in and out by plotting a section that explain that. [There must be some dead point having zero velocity due to low rotating speed (47rpm).]
The idea of "generate its own flow" is little bit confuse for me.
Here is what I done lately:

CFD 3D Viewer file: aerator

ghorrocks May 21, 2012 08:24


Thanks a lot for your car ghorrocks
I gave you my comments, no my car. I need my car to get to work tomorrow :)

Use periodic interfaces, not symmetry planes. Have a look at the turbo machinery tutorial examples for how to set this up.

You correctly say you need something for the flow to react against otherwise it will just rotate at the impeller velocity - in this case you set the bottom and outer walls as counter rotating walls, which in a rotating frame of reference means they are stationary.

luai May 23, 2012 04:48


Originally Posted by ghorrocks (Post 362195)
I gave you my comments, no my car. I need my car to get to work tomorrow :).

:):):) got what i meant, right!

thank again for your care, I'll do it from the beginning.
hope to be just fine.


luai May 24, 2012 04:57

needs some help with the setup configurations
ghorrocks, I made” Multiphase Flow in a Mixing Vessel” tutorial and it helps a lots. Thanks
For the setup solation:
But the results did satisfy me enough, there is something wrong with boundary or interfaces maybe!?
I made an impeller domain (rotate at 47 rpm) and lagoon domain (stationary), without inlet and outlet boundary; i take the buoyancy effect too.
I configure Periodic surfaces to the lagoon and the impeller domains, and all interfaces in the impeller domain. Till now everything being good, at least I guess!!
For the results:
The water must get in from the bottom of the impeller and get out from the passages to lagoon, and that not happen!! The angular velocity is right i check it.
The Torque is very small.
I don’t know what’s wrong; I relay need some help with the setup configurations for the modal.

ghorrocks May 24, 2012 07:22

Many of the other tutorials will also be of assistance. Have a look at free surface flow over a bump and some of the rotating machinery tutorials.

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