No pressure difference is shown in air cylinder compressed by a piston

[hs.simanto]

Hi!

I tried to simulate pressure difference inside a cylinder filled with air(compressible) due to force exerted by a piston.

Pressure should change if the air is compressed according to the rule PV=k.  But there were no pressure change as well as its showing air in the piston's previous position which should be compressed.

CFZ file is upload for your better understanding about my approach.

Thanks.

[Royce_adsk]

Hi Simanto,

Some quick edits to your geometry:

This helps align your geometry on best practice for motion and setups your diameter of the piston to always cover your air as it is driven downwards.

Make these changes and upload a new support file for me to review for you.

[hs.simanto]

Hi!  Royce!

Thanks for your reply.

I modified my geometry as you instructed.

After running my simulation as i approached, velocity and total pressure results are illustrated like the attached photos.

I also uploaded the CFZ file for you to review for me.

Thanks 🙂

[Royce_adsk]

Hi Simanto,

You will need to make the piston long enough to cover the fluid once the piston has gone far enough into the model. Keep in mind the mesh masking approach that motion is using to model the physics. 

Best regards,

[hs.simanto]

Hi!

thanks for your review. I made the model as you instructed. I compressed the air volume inside the cylinder to half of its initail volume. Pressure should be twice of the initial pressure as the Pressure Volume relation stands for PV=constant. But my model solution isn't showing that... instead its showing pressure 1.5multiple of initial pressure.

Initial pressure

Final pressure


CFZ file is attached for your review. thanks 🙂

[apolo_vanderberg · Accepted solution]

I havent looked at your sharefile yet, however typically for these this is the one situation where we need to step up the number of Inner iterations for Motion.

By default this is 10 for transient models, but set to 1 for Motion models. To do a proper compression model we need to set ~15inner iterations, this should help raise the computed pressure rise.

[hs.simanto]

Hi!  apolo. vanderberg

Thanks for your reply. I run the same simulation with increasing the number of inner iteration to 15 and now my result are satisfying 🙂
Initial Pressure


Final Pressure




I can visualize the pressure rising to a value which is twice the initial value as the volume of air is compressed to half of its initial volume.

Thank you very much !! 🙂 🙂