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Old   March 26, 2020, 14:18
Default Piston-fluid simulation
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hi guys,i want to simulate fluid (in fluent) that enter into a cylinder which have a piston linked to a spring that have a stiffness and a preload.
once the fluid enter in the inlet the piston will move to the right until the spring overcomes the force applied by the fluid.
i think that i shoud use dynamic mesh but i really need guiding.
help
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Old   March 27, 2020, 03:15
Default Piston
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Fluent has a 1DOF model based on 6DOF. It has an inbuilt spring model as well. You can make use of it.
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Old   March 27, 2020, 07:20
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u mean 6dof option using dynamic mesh ?
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Old   March 27, 2020, 07:45
Default 6dof
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Yes, that's what I meant. Within 6DOF, it has a 1DOF option which is meant for scenarios similar to yours.
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Old   March 31, 2020, 11:22
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hi, i'm entering a fluid in a cylinder with profile of pressure p(t) and i want to see how fluid in moving in the cylinder due to the force of the pressure.
any help ?
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Old   March 31, 2020, 11:28
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That's exactly what 1DOF (or 6DOF) simulation does. Look for a tutorial on this; most likely it is available on ansyshelp.ansys.com
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Old   March 31, 2020, 16:24
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i 've seen tutorials w they are all defining new interfaces.
i don't know why ?
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Old   April 1, 2020, 03:15
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There is a reason for the interfaces, however, interface requires an external domain, which you don't have. If the wall of the cylinder is an interface, piston can slide easily and no mesh deformation is required, however, this requires a domain outside the piston wall. You may create a thin solid layer representing cylinder to use that methodology. Better option is to define the wall of the cylinder as deforming. The reason it is deforming is because its size is changing as the piston moves up and down. The meshing in the fluid region can be controlled either via layering, if mesh is made of prisms (quad or tri), or via remeshing, if mesh is made up of tet cells.
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Old   April 1, 2020, 11:34
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As a beginnig i want to model the problem in 2D as u can see in the attached photo . in the orange zone, between the piston and the fluid, there is a contact? what kind of boundary condition should i make there ?
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Old   April 1, 2020, 12:20
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Piston's crown is no-slip wall. Model it as axisymmetric. 2D planar implies a rectangular piston.
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Old   April 1, 2020, 17:04
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Hi again,
For the inlet which is a wall, i want to enter a pressure profile , i read it then when i want see th motion, it seem like "Warning: Can't identify any field of profile pressProfile.
No motion specified."
i wonder if there a way to enter a pression via that wall
that inlet wall in used in the dynamic mesh and will be the reason of the defomation in the fluid
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Old   April 3, 2020, 10:54
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i enter at first inlet as pressure inlet w i have the same problem, fluent can't read it as i guess.i'm stuck in this pb for a good while.
if u have any idea that could help me i'll appreciate that.
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Old   April 6, 2020, 05:58
Default Inlet as wall
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Inlet should be inlet and not wall. No fluid can enter through a wall. If, for any specific reason, you want to model inlet as wall, then you have to provide some source term to increase either the volume, which can be due to increase in the mass or the pressure.
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Old   April 6, 2020, 07:40
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that's mean that we can't apply pressure in a wall.
i apply pressure in the inlet as well and i putted fluid as deforming in the dynamic mesh but also there is no movement in the fluid
and i get this warning ; Can't identify any field of profile pressProfile.
No motion specified."
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Old   April 6, 2020, 07:46
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Even in real life, no pressure can be applied by a pressure until and unless the wall moves, e.g., the walls of a container or a room. The only way a walls can cause such a thing is if it is porous or if there is some reaction occurring that increases the mass or the temperature, which in turn increases the pressure.

No cell zone should be defined as deforming zone. It should only be boundaries that need to be defined as deforming. Cell zones could have a motion defined though. However, for your case, it has to be done via one-DOF. I hope there are tutorials available online for this.
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Old   April 6, 2020, 07:59
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what do u mean by 'It should only be boundaries that need to be defined as deforming.' ?
1DOf can be applied only for rigid body as i know w not a deforming fluid
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Old   April 6, 2020, 08:14
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In Fluent, you need to define the boundaries that deform or move. For the deforming options, only boundaries should be selected. E.g., in your case, the size of the fluid region will increase, in other words, it will deform. But you should not define this cell zone as deforming. However, the sides of the cylinder must be defined as deforming.
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Old   April 6, 2020, 08:31
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ah ! ok i get it i 'll try that. thanks for the explanation
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Old   April 6, 2020, 11:28
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hey again,
if i i have understood well,
this is the fluid (oil)
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Old   April 6, 2020, 11:32
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I suppose the following tutorial should be able to help you

https://www.youtube.com/watch?v=aO1a4-Zm7Ag
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