Learning Forum

[Max4]

Hello,

I want to simulate the movement of the piston in black. Around the piston there is an inflation layer, which moves with the piston and set as rigid body in the dynamic mesh.

In the dynamic mesh zones, I set wall_p_1 and wall_p2_ as Deforming, and the simulation works well right down to the corner. The wall_p_1 belong to the inflation layer.

The problem is that I get negative cells in the corner (see the mesh below)

My question is, is this coming from the wall and the software doesn't understand that it has to continue? I want to have a situation like below.

Regards,

Maxime

[Amine Ben Hadj Ali]

Is it possible to use "Deform Adjacent BL with Zone" for piston and using deform for the cell zone and walls?

[Keyur Kanade]

this looks tricky. i have not tried this anytime. 

you may need to decompose the geometry so that you you have a wall_p_3 when piston goes up. wall_p_3 = wall_p_1 + wall_p_2 in your last image. 

you may try with non conformal interface at wall_p_3. 

[Max4]

For this simulation, I have used "Deform Adjacent BL with Zone" for the piston and Deforming for the cell zone (mesh) and walls.

I have tried to merge the wall_p_1 and wall_p_2 but it doesn´t work.

How can I create this wall_p_3?

 

[Keyur Kanade]

you may need to do it at geometry level

[Max4]

I have to create two cell zones, and set this wall_p_3 as an interface? In Create/Edit Mesh Interfaces, may I have to use the function "Coupled Wall "?

[Raef.Kobeissi]

Coupled wall for heat transfer purposes?

[Max4]

Hi,

I´m trying another approach, where the walls don´t overlapp. Let us consider the following system:

In the dynamic mesh setup, I have:

Piston - Rigid Body (UDF Piston)

Wall_p_1 - Rigid Body (UDF Piston)

Wall_p - Deforming (Layering?)

Fluid_around_wall - Stationary

Fluid_around_piston - Rigid Body

Fluid_around_wall_p - Deforming

Fluid_rest_domain - Deforming

 

• Around the piston (black), I have an inflation with 1 layer. I have an inflation around the wall (blue) too.


• Around the wall_p_2 (red) and wall_p (green), I have create another zone (in DesignModeler), in order to have quad cells on the wall


• The rest of the domain is composed of triangular cells

When I try to run this, I obtain the following situation. Inflation, which is supposed to remain fixed in relation to the piston, deforms. On the corner (picture 2), the inflation around the wall is deforming even if it´s as Stationary.

 

Regards,

Maxime

[Amine Ben Hadj Ali]

The answer to the original question would be to use non-conformal interface as you a topological change.

As the piston travels over the edge, the elements become negative. The only solution is to build a non-conformal mesh whose interface is a bit longer than the piston movement. 

Without looking into the case will be hard to give any other suggestions here. As ANSYS Stuff we cannot download attachments and would not work on any cases. Perhaps one non ANSYS-Stuff can help you there.

[Max4]

Thank you for your answer. I have extended the length of the wall_p and delete the corner in order to avoid the overlapping. The problem is that I have to have inflation or quad cells around walls for a better convergence of the solution and for the examination of the boundary layer.

I´m facing another problem with the movement of inflation which should be attached to the piston.

Moreover, I´d like that the quad cells attached to the wall_p deform (using Layering) according to the movement of the piston. The problem is that I cannot choose just the quad cells attached to the wall_p and then the wall_p and wall_p2 are moving at the same time.

 

Regards,

Maxime

 

[Keyur Kanade]

as suggested in my previous post 

you may need to decompose the geometry so that you you have a wall_p_3 when piston goes up. wall_p_3 = wall_p_1 + wall_p_2 in your last image. 

you may try with non conformal interface at wall_p_3. 

 

recommend you to us only tri mesh first. once you are successful with tri mesh then you can think of adding prisms.  

[Max4]

Thank you for your reply.

I have understood, that I have to use non conformal mesh, but I´m not facing this problem yet.

The problem is the add of prisms around walls, especially along the wall_p.

I have separate the cells by shape (iso-value) and then seperate the shape composed of prisms in inflation around the piston or the wall. The problem is that all the prisms moves when I run a simulation.

[Max4]

Hi,

The system is as follow. I have separate the geometry in 3 zones in DesignModeler.

Green: Fluid_Remeshing - Deforming (Smoothing and Remeshing)

Orange: Fluid_prism_piston - Rigid Body

Grey: Fluid_prism_wall - Deforming (Layering)

 

The red line is the wall and I have set it as Deforming (Layering)

The black line is the piston and I hav set it as Rigid Body and it moves thanks to a UDF.

When I run a preview mesh motion, the Layering on the Fluid_prism_wall (grey) doesn´t work and I don´t know why.

 

Regards,

Maxime

[Keyur Kanade]

the prism on left side walls will not be remeshed. 

please remove prism on left side wall. 

[Max4]

Why can't these cells be remeshed with Layering?

I have to keep this prism cells on the wall in order to guarantee a better convergence of the solution and for the examination of the boundary layer.

[Keyur Kanade]

then you have to have that cell zone as different than tet. also there should be non conformal between tet and quad. then you can use layering for quad and remeshing for tet. 

please try without prisms on left side wall and check how it goes. 

[Max4]

I have created 3 zones in DesignModeler. Then I created different cell zones in Fluent using Mark/Adapt and Separate.

 I used Layering for the cell zone along the wall, and Remeshing + Smoothing for the cell zone with tet cells.

[Keyur Kanade]

you need to have non conformal between left side prism and tet

[Max4]

Should I do it in Fluent or in Meshing ? I have found this: http://www.afs.enea.it/project/neptunius/docs/fluent/html/ug/node189.htm (Using a non-conformal mesh in ANSYS Fluent).

The bold green line is the interface between prism cells along the wall and the tet cells, but it´s set as Interior and I can´t change it as Interface.

 

In DesignModeler, I have grouped the different bodies in 1 part, so that Fluent knows that all parts represent the fluid.

 

 

For create the different zones in DesignModeler, I used in Operation "cutting material". Is it better to use "Add frozen" or "Add material"?

 

Regards,

Maxime

[Max4]

Hi,

I have created an Interface (in yellow) in ANSYS Meshing (picture 1). Then I have separate the prism cells (rper:015 and rper:005) along the wall on the left side (picture 2).

The fluid should cross this interface, thus what Option should I use in Mesh Interfaces in Fluent? Should I create 2 Interfaces, one for each zones ?

 

Regards,

Maxime

[Keyur Kanade]

there should be interface between left side prism and bottom prisms

[Max4]

When I have created it, what should I apply to this interface?

[Keyur Kanade]

yes, you should apply interface. 

[Max4]

I should apply "Interface" as Type, and then should I still done anything else?