CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > CFX

Simulation of rotating pistons

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   March 12, 2013, 09:33
Default Simulation of rotating pistons
  #1
New Member
 
Join Date: Mar 2013
Posts: 4
Rep Power: 3
donalffons is on a distinguished road
Hi everyone!

I'm a beginner with Ansys / CFX and after completing a bunch of tutorials and doing some simple analyses, I am struggling now with the following problem:

I want to simulate the rotation of the pistons of an axial piston pump (like this one). For simplicity, I broke down my problem to what you see in this picture:

The point is to simulate, how the rotating parts influence the fluid. The goal is to find out, how much drag force is created by the system. Until now, I fail to set up the system in CFX-Pre.

I tried several things here:
- Stationary fluid domain & rotating walls: This doesn't work, because the walls are not allowed to have normal velocity components
- Rotating fluid & stationary / rotating walls: I tried around with some boundary conditions, but the results were always not as expected
- Immersed solid (and a different mesh): This worked, but the results were quite incorrect. For example, I got result forces in X-Direction

So, I'm lost here. Can anyone give me a hint on how to solve this? Or should I take a somewhat different approach?

Last edited by donalffons; March 12, 2013 at 14:02.
donalffons is offline   Reply With Quote

Old   March 12, 2013, 13:59
Default
  #2
New Member
 
Join Date: Mar 2013
Posts: 4
Rep Power: 3
donalffons is on a distinguished road
...for example: When I simulate the problem with a rotating fluid domain, the shaft and pistons as no-friction walls and the housing as a counter rotating wall, I get this as a result (velocity contour):

... which is not what I expect, of course. Since the fluid should move much faster near the center, where the rotating parts are.
When I change the contour plot to velocity in Stn Frame it looks like this:

...which kind of looks like what I am aiming for. I'm still not quite sure, if this is the right way to do such an analysis and if it actually captures what is happening physically. Can anyone tell me, if what I'm doing here is going into the right direction?
donalffons is offline   Reply With Quote

Old   March 12, 2013, 18:24
Default
  #3
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 9,594
Rep Power: 76
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Have a look at the tutorials for the difference between velocity and vel in stn. frame.

Are you trying to simulation the region between the swash plate and the cylinder block?
ghorrocks is offline   Reply With Quote

Old   March 12, 2013, 18:42
Default
  #4
New Member
 
Join Date: Mar 2013
Posts: 4
Rep Power: 3
donalffons is on a distinguished road
ghorrocks, yes, the area between the swash plate and the cylinder block.

I will do have a closer look at the tutorials tomorrow. Probably the multiphase mixing vessel could be a good start...
I would appreciate any comments and advices on my case setup, since I'm totally not familiar with Ansys and CFD software in general.

After the simulation, I want to extract the resulting drag moments with the torque_x@... functions.
donalffons is offline   Reply With Quote

Old   March 12, 2013, 19:11
Default
  #5
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 9,594
Rep Power: 76
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
The motion will be tricky. You might need to use moving mesh to model it. But, depending on what results you are looking for you might be able to simplify it to a frozen rotor model. That would be much easier, simpler and quicker - if it is appropriate.

Do the tutorial examples on moving mesh and rotating franes of reference to get a feel for these techniques.
ghorrocks is offline   Reply With Quote

Old   March 12, 2013, 19:36
Default
  #6
New Member
 
Join Date: Mar 2013
Posts: 4
Rep Power: 3
donalffons is on a distinguished road
I played around with moving mesh simulations a few days ago, but I really had a hard time in getting the simulation to succeed (because of the negative volume error message). So I actually was hoping to avoid this kind of simulation...
I will investigate on the frozen rotor issue + rotating frames a little more. Thank you for your input!
donalffons is offline   Reply With Quote

Old   March 12, 2013, 19:40
Default
  #7
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 9,594
Rep Power: 76
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Yes, movign mesh simulations are tricky to avoid folding the mesh. But that is going to be the most accurate way of modelling it.
ghorrocks is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Simulation and Optimisation of centrifugal fan 3D to 2D eRzBeNgEl STAR-CCM+ 0 January 31, 2013 13:21
errors in simulation with a rotating bowl qq216 OpenFOAM Running, Solving & CFD 0 January 26, 2013 11:30
simulation results don't match with experimental results funquest CFX 2 January 19, 2013 20:24
transient simulation of a rotating rectangle icesniffer CFX 1 August 8, 2009 07:25
Rotating Arm Simulation fluentnoob FLUENT 0 June 23, 2009 10:56


All times are GMT -4. The time now is 00:52.