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

Rigid Body Motion + Remeshing

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 22, 2017, 06:24
Default Rigid Body Motion + Remeshing
  #1
New Member
 
Ganesh Narayana
Join Date: Oct 2015
Location: Bengaluru
Posts: 12
Rep Power: 7
Ganesh.aero is on a distinguished road
hi all!

Am trying to simulate a jerk type fuel pump, it basically contains a plunger which compresses the fluid against a valve (supported by a spring at its back) which opens only when the pressure build is sufficient to overcome the spring stiffness of the valve spring.

I have taken a rigid body solution for the valve movement as it is determined by the fluid forces acting on it.

Since the valve displacement is large re-meshing had to be used, the domain around the valve body is taken as the re-meshing zone & ICEM Replay script file has been used.

The valve displacement output monitor using an expression for total centroid displacement has been set up which is used as a scalar parameter for ICEM CFD Mesh control.

The re-meshing criteria has been set using an interrupt condition using an expression for min. orthogonality angle < 15 deg.

A profile data for the plunger movement has been read using a csv file.

The total time is 0.00896sec with 30 time steps.

The rigid body solution is calculated every co-eff loop with 10 iterations per loop.

I have setup time-step initialization in solver to previous & to use latest mesh for mesh deformation under the interpolator in advanced settings in the global initialization using CFX solver.

"The calculation stops after only 1 time step every-time" Displaying a message saying the run has finihed normally.

Am loading the previous time step result as initial values for the next time step & solving.

How to Solve this?
i also get this message: ERROR- problem interpolating results onto new mesh file.

Any suggestions
Ganesh.aero is offline   Reply With Quote

Old   February 22, 2017, 16:48
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 16,642
Rep Power: 130
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough
I would probably split this simulation into two:

First a moving mesh only (no rigid motion stuff) to do the compression stroke with the valve fixed shut. When the force on the valve is high enough to overcome the spring force I would stop this simulation then restart on a second simulation with rigid body activated on the valve and the valve should move straight away.
ghorrocks is online now   Reply With Quote

Old   February 23, 2017, 05:51
Default Tried it but pressure ain't increasing!!
  #3
New Member
 
Ganesh Narayana
Join Date: Oct 2015
Location: Bengaluru
Posts: 12
Rep Power: 7
Ganesh.aero is on a distinguished road
I had made the valve as stationary walls & tried to compress the plunger region, but the pressure was initially high in the first time step & decreased thereafter. Don't know why.
my simulation undergoes remeshing even when the interrupt condition of min ortho angle is not fulfilled.
is it even possible to employ rigid body motion with remeshing & moving boundary?
am using ICEM CFD Replay script for remeshing, with a replay file, have created a part for valve part mapping in the geometry control & have used mesh displacement ( the output monitor) as the scalar parameter for mesh control.
Do i need to alter that? because it gives me this error saying interpolating results on to new mesh is not possible.
For some cases it says CFX solver input file does not exist, again dont know why?
can you please tell me how to use remeshing with ICEM Replay file properly?
Ganesh.aero is offline   Reply With Quote

Old   February 23, 2017, 16:53
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 16,642
Rep Power: 130
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough
It appears you have multiple problems (strange pressure behaviour and remeshing not working).

In that case you should simplify this simulation so you have only one issue to deal with. So do a simulation with no remeshing and fix the pressure problem. Once you have fixed that then do a remeshing problem with a very simple flow. Then when both problems are resolved you combine the two into a simulation which has both issues fixed and you can run your entire simulation - and you are bound to run into problems with the combination of the two models as well.

Trying to debug a simulation with multiple problems is very difficult.
ghorrocks is online now   Reply With Quote

Old   February 24, 2017, 02:51
Default have tried immersed solid approach
  #5
New Member
 
Ganesh Narayana
Join Date: Oct 2015
Location: Bengaluru
Posts: 12
Rep Power: 7
Ganesh.aero is on a distinguished road
Hi there!

I came across this approach called immersed solid approach as it is true of my case where the valve inside the fuel pump is completely immersed in fuel. The next component that follows a fuel pump is a fuel injector. I thought the pressure is strange because of improper value ( 0 Pa, w.r.t relative pressure) given at the the fuel pump outlet.
Don't you think at the fuel pump outlet, the pressure value to be given has to be the pressure of the environment it flows into?
because at 0 Pa at outlet the rigid body motion is not happening at all & i increased the outlet pressure to around 1800 psi (which is generally the pressure inside a fuel injector), i can see some valve displacement but very small though.
Ganesh.aero is offline   Reply With Quote

Old   February 24, 2017, 05:53
Default
  #6
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 16,642
Rep Power: 130
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough
I have not seen what you are modelling or how you modelled it so cannot say in your case. But in general for high pressure fuel injection the outlet of the pump is at high pressure (say 1800psi) and the fuel system from the pump to the injectors are at approximately that pressure. There will be some dynamic wave effects and I am not sure exactly how large they get, also flow losses along the way.
ghorrocks is online now   Reply With Quote

Old   February 24, 2017, 06:23
Default Moving wall ain't moving now!!
  #7
New Member
 
Ganesh Narayana
Join Date: Oct 2015
Location: Bengaluru
Posts: 12
Rep Power: 7
Ganesh.aero is on a distinguished road
Take a look at the pictures, may be that'l help, the moving wall compresses the fluid (which is at 1 atm) inside which further pushes the valve, the velocity of the moving wall is 0.62832 m/sec. my moving wall section should compresses itself because of the specified displacement given to it using an expression.
From the figure you can figure out that the outlet is a little far from valve. Though there is rigid body motion but the moving wall ain't moving 2.PNG

3.PNG
Ganesh.aero is offline   Reply With Quote

Old   February 25, 2017, 05:53
Default
  #8
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 16,642
Rep Power: 130
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough
It is difficult to handle valves cracking open (or shutting) as the mesh gets squished into oblivion. You need to do something to handle the case for when the valve is only open by a tiny amount.

The approach I recommended in post #2 is good here, because you can start the second simulation with a moving valve with the valve already open enough to put a reasonable mesh in it.

You can also do it using interfaces, source terms, and functions to make the first opening big enough to be meshable. But I would try the suggestion in post #2 first because it is easiest.
ghorrocks is online now   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Rigid body motion in the polymer flow Igorenia Fluent Multiphase 0 March 30, 2016 15:42
Problem with rigid body motion ghost82 EnSight 11 March 12, 2015 09:22
Rigid Body motion?? arun7328 STAR-CCM+ 15 November 14, 2013 02:19
Dynamic Mesh Modeling - Six Degree Rigid Body Motion bluewings OpenFOAM Running, Solving & CFD 0 February 12, 2013 20:08
Using solidBodyMotion for rigid body motion L1011 OpenFOAM 4 July 5, 2011 04:59


All times are GMT -4. The time now is 06:42.