Problem with a 2D geometry

[Anonymous]

Hello to everyone,

I am new CFD user, and i need some help with a simple 2D geometry.

I want to simulate the flow between a stator and a rotor. The problem is that simulation CFD 2015 seems to calculate velocities and pressure where there is not fluid, and the results doesnt seem to be accuracy.

Please, help!!!.

I have attached the support file. 

Lot of thanks to everyone!

[Jon.Wilde]

Hi,

I'm sure we can help. Need to take a step back and ask a few questions first though.

I guess I am a littlle confused by the axisymmetric in Y choice, was that deliberate?

What is it that you need to know from the CFD analysis? Just to see the flow or get something quantative?

Could I also ask if you have run through any tutorial models from the help?

I am guessing that this should simply be a 2D model, in which case I think this article and associated links will be most useful:

Rotating Region Best Practices

Thanks,

Jon

[srhusain]

There are some things you need to do to set up the model properly:

1. Materials- you only have two parts, i am assuming that the stainless steel is the one that is rotating. One approach would be to enlarge the water part to enclose the steel and then enclose these parts inside yet another water part which can be a square domain. Then you would reassign a rotating region to the parts comprising the annular and enlarged water part (you can leave the steel part as before), During the assignment of the rotating region, you need to decide if you want a constant speed or some other behavior. The constant speed needs a RPM value and is the simplest to start with.
2. Boundary conditions- assign zero pressure on the left and right end of the square domain.
3. Run the analysis.

Please consult help documentation or tutorials that will help you on a step-by-step basis.

Hope this helps.

[Anonymous]

Hi,
First of all, thank you for answering so fast.
The Y axysimmetric is because i tought it doesnt matter if it should be X
or Y, because it is a circle geometry. Even so, if i only use 2D geometry
(no X or Y axyssimmetric) it gives me the some problem.
>From Inventor i take de 2D CAD, and it seems to difference the 3 parts
(stator, water and rotor). But when i run the solver, it seems that water
is also in the rotor part, because if i hide it in the results, i can see
velocities and pressures (and it doesnt happens in the stator part).
Answering your question, i want to simulate the flow and take something
quantitative (i began simulating the 3D problem, but i thougt it would be
useful to begin with a 2D geometry)
And, finally, yes, i have seen lot of tutorials, but i could not find 2D
tutorials.

Lot of thanks again, and sorry for my english, it isnt really good.

Javier

[srhusain]

The rotating region is also water and you will see non-zero velocities in this region- this is normal. What is meant by the phrase "rotating region" is that the coordinate frame attached to same is actually rotating bu that the fluid in this region may not exactly follow the rotation as in Omega Cross R, where Omega is the (prescribed) speed of the rotating frame.

To see the velocities in the "stator" part, you need to run the analysis with a sufficiently small time step and at least 150 time steps, such as "3-degrees per step" which is available in the solver dialog.

[Anonymous]

the problem persist although using motion instead of rotational region, using ADV5 and a really small time step :S

[Jon.Wilde]

Use a rotating region, this way we can still have a boundary layer in the mesh and this problem should go away, far better 🙂

Also, the 2D setting as you now have it is OK.

Axisymmetric assumes that it is symmetric around an axis also, so this was initally a toroid in shape - I could not get my head around how this could be built 😄

[Anonymous]

but using rotation region, the program seems to see the rotor (which is a solid part) as it was fluid, because there are pressures and velocities.