ghost wall, dynamic mesh

  • Last Post 27 March 2019
vmiglietta posted this 23 January 2019

I want to see the flow disturbances caused by a solid disk moving  in a fluid.  I have a disk mesh that moves relative to the fluid around it.  The disk is on the bottom of a cylinder of water.

In solution animations I see the disk move however it's walls do not appear to affect flow.  Vectors and pathlines of the solution go right through the disk.  The disk is set as a wall and its material solid aluminum.

Why does the disk act like a ghost, no showing any affect on the water around it, in solution animations?

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rwoolhou posted this 23 January 2019

Please can you post some images of the results and mesh? 

kkanade posted this 24 January 2019

please insert detailed zoomed in images and explain the issue. 

please try to reduce arrow size in vectors and check. 

vmiglietta posted this 24 January 2019

Hi, I posted one image of the disk mesh so you can see its approx size and location.  The other image is a slice at z=4cm which should cut right into the disk.  I don't know what kind of helpful detail a more zoomed image would show.  The flow shows no indication of there being an obstruction to the flow.

The tank is rotating. The disk is also rotating around the center of the tank (the disk is located at about 0.5r from the center of the tank).  The disk is moving very slowly in the opposite direction which the tank is rotating.

Any other pictures that could help solve this problem?

rwoolhou posted this 24 January 2019

Please can you post them as inline images? Use the insert image option: as staff we're not allowed to open attachments. 

vmiglietta posted this 25 January 2019

abenhadj posted this 25 January 2019

You need to assign the fluid walls (in connection)  with solid walls (in shadow) the same rotational motion as the solid itself.

Best regards,


rwoolhou posted this 25 January 2019

Did you do any split/subtract operations in Meshing? Fluent can read overlapping meshes and if you don't do anything to connect them will usually solve on both/all without any errors: strictly there's nothing wrong as the import is technically valid. 

vmiglietta posted this 25 January 2019

I don't understand what you mean by "in connection" and "in shadow".  The 2 cell zones are fluid, solid. 

The fluid is in rotational frame motion, relative to the absolute.

The solid is in rotational mesh motion.  Its motion is relative to the fluid cell zone.

Fluent only allows me to modify the boundary condition of the wall of the fluid.  The only option is to have the fluid wall move relative to the adjacent cell zone. 

Any suggestions?

rwoolhou posted this 25 January 2019

Have you got a wall - wall:shadow pair on the solid surface? 

vmiglietta posted this 25 January 2019

I don't know how to specify a boundary wall which will have a shadow.  This is done in meshing not geometry correct?

vmiglietta posted this 28 January 2019

No I did not split or substract anything.   I made two cylinders.  One large one for the tank, and one small one for the disk.  They are both very simple and dont need high resolution mesh. But fluent gives finer mesh to the small cylinder anyway.

vmiglietta posted this 28 January 2019

I've looked into this wall, shadow thing.  The closest thing that appears is wall and interior.  but for the cell zones only 2 appear, one for fluid and one for disk.  Please can you help me set up the disk so that it obstructs flow?

I've tried to setup a contact between fluid and disk in the mesh edit but it does not make any difference in the fluent setup.   I am not looking at what occurs at the boundary of the disk but at the greater area surrounding the disk.

Thank you for your help.

rwoolhou posted this 28 January 2019

Right, what you've got is two disconnected meshes - the flow goes through the large cylinder and the solid moves based on your code. As they're not connected the two volumes don't know about each other. 

You need to subtract the solid and then set up remeshing in the larger domain to move the walls. Have a look at tutorials etc on YouTube and notes in here for moving deforming mesh. 


vmiglietta posted this 12 February 2019

not moving togetherThe two contact regions do not move together. I do not know how to remedy this.  I have the rotating defined in CELL ZONE CONDITIONS . Do you know how I can get them moving together?

vmiglietta posted this 12 February 2019

Thank you.  I have done what you suggested.  I have watched a few tutorials and only in 2D tutorials it is shown how to move walls.  The 3D tutorials do not address how to move walls. In 3D I cannot find how to set walls as moving walls.   I posted a photo of the interfaces not moving together.  The outer region of the zone moves however the void made by the boolean appears to stay put. Any suggestions as how I can make my the contact regions moving together?

vmiglietta posted this 11 March 2019


    I followed a fan tutorial and made a region where the object moves.  I set up the mesh and regions like a fan with one blade.  And it works with no mesh issues. However the speed I set the object to move at, also sets the fluid in the region it moves through to rotate at the same rate.  After some time, about 10 sec,  the rotation of the tank that the object is in does take over the fluid motion (in the region the object moves through).  But the physics of the model is wrong. The water above the moving object is supposed to be stagnant, the entire column above the moving object.  This had to do with the rotation of the fluid and the slow rate the object is moving at.  But water keeps flowing right over the object. 

rwoolhou posted this 11 March 2019

Are you plotting absolute velocity? 

vmiglietta posted this 11 March 2019

tangential velocity

vmiglietta posted this 27 March 2019

So the solution to this was to define the region the object moves through; define this in the meshing process. The object moves but I guess the contact region does not move, it needs to be defined through the entire path the object is moving through.