[sanjeetlimbu]

I am trying to simluate the compression stroke by a piston using 2D axisymetric.
Currently i am trial s fo rthe 2D planner mesh using the dynamic mesh - profile mode, I created the profile by using the time and velocity for 1440 points from matlab taking time step as 0.000041667s.

But I am unable to get exact mesh motion. I got the zone motion correct.
The piston has crevice shape- I made two cellzone- body which defoems and crevice - as moving mesh.

I did the following: Cell zone- crevice .set as mesh motion type, and set write profile- having motion history points which also will be used for rigid bodies
Piston – as moving wall in boundary condition(piston is of two part its inteface with body and crevice both moving)
The dynamic mesh- piston as rigid body- profile selected,
Body- as deforming layering only, unchecked the remeshing and smoothening
Crevice as rigid body- profile selected.

I using the profile define to get the dynamic motion.. average velocity is 9m/s to max 14m/s
But when i using the preview mesh motion I am getting the negative volume error. even i tried to reduce the time step to 4.1667E-8, also getting the same error
Please tell how to do mesh


please help me I am not able to do anything ..
it seems that the crevice part get blocked by the body mesh as seperate and it donot reduce the volume

[sanjeetlimbu]

I am getting negative volume error during the dynamic mesh motion preview

[sanjeetlimbu]

Please share some update on how to make it work....

I tried some simple case by removing the crevice part- just the cylinder- 2D rectangle, then using the edge sizing and mesh mapping... it size as 0.0001 mm.
I was able to do mesh motion preview for very small time step 4.16E-07s.

So the issue seem to be due to the mesh interface between the body and the crevice part at that wedge shape. Can you please tell how to make it work in dynamic mesh motion to avoid negative volume error

[acimino]

I think that your problem is that you are defining both a sliding mesh and a deforming mesh. As far as I know, that is not possible in FLUENT 18.

A sliding mesh does not change the shape of its cells, but it moves relative to another block of cells (e.g., when you model a turbomachine, using a static block of cells for the inlet and a block of cells fixed to the rotor, see FLUENT's theroy guide). Such meshes can be created using the tab moving mesh in cell zone conditions.


what seems to be happening is that the crevice's mesh is being superimposed to the other one because of its motion.

I gues you need to find a different approach.

Hope it helps