Immersed solid with cavitation

shivasluzz · June 4, 2015, 23:42

I am doing a simulation of gear pump with low inlet pressure condition.
I use 2 fluids (liquid and vapor) and set saturation pressure to account for the 'cavitation effects'.
The solver says 'immersed solid with muliphase combination' is not supported. But the solver runs and converges. Can I use the result or not?
In help documentation, it is given that 'mulitphase flow does not properly INTERACT with immersed solid'.
Here "INTERACT' means what?
I want to check only the reduction in mass flow if cavitation occurs? So can i use the result?

shivasluzz · June 5, 2015, 08:05

the results are converged to the sufficient accurancy (rms : 1e-6)...
i could see the pressure of vapour also..
but there is only one warning during starting that 'Warning: You have used Immersed solids with Mulitphase option. This combination is not supported'
Is that solution is totally wrong?

ghorrocks · June 6, 2015, 00:47

If the fluid cavitates then yes, you results are likely to be completely wrong. Immersed solids cannot account for varying density. But if you do not cavitate or the cavitation volume is small then you might be OK.

shivasluzz · June 9, 2015, 10:42

Thanks ghorrocks for your reply! Then I think deforming mesh is the only option.. But is it possible to simulate Gear mesh motion?

ghorrocks · June 9, 2015, 18:34

For a gear pump that will be tricky. the only way it is going to work is with dynamic remeshing.

shivasluzz · June 9, 2015, 23:10

Dynamic remeshing? Is is not same as Mesh displacement?

Please share some link or some similar example...

ghorrocks · June 9, 2015, 23:26

Moving mesh is where the mesh topology remains the same but it is distorted to move. It is only suitable for small ranges of motion. Dynamic remeshing is where moving mesh is used up until the mesh quality drops below a defined criteria, then a remesh is triggered and a new mesh generated and the simulation continues on the new mesh. This obviously involves interaction with the meshing software.

I think there are example dynamic remeshing simulations on the ANSYS customer webpage. ANSYS support will also have some I suspect.

vivjk94 · December 30, 2021, 08:12

Quote:

Originally Posted by shivasluzz

I am doing a simulation of gear pump with low inlet pressure condition.
I use 2 fluids (liquid and vapor) and set saturation pressure to account for the 'cavitation effects'.
The solver says 'immersed solid with muliphase combination' is not supported. But the solver runs and converges. Can I use the result or not?
In help documentation, it is given that 'mulitphase flow does not properly INTERACT with immersed solid'.
Here "INTERACT' means what?

I want to check only the reduction in mass flow if cavitation occurs? So can i use the result?

Hi, I would like to know how did you model the cavitation in gear pump? I hear you can do it in fluent. If you have solved your problem please share your procedure and computation time. I am also in same problem.

Gert-Jan · December 30, 2021, 08:28

You can do gear pumps in CFX using the Twinmesh technology (https://www.twinmesh.com/)
Alternatively do this in Fluent (or Star-CCM+) using Deforming mesh or Overset-Meshing.
All approaches are difficult and require a lot of perseverance.

Using Immersed solids is a bad idea. The solids only affect the velocity of the continuous phase, and completely ignore Volume fractions, temperatures, and other scalars. They go though the solids as if there are not there.
Therefore, its applicalbility is quite limited. Only use it for a very rough approximation.

June 4, 2015, 23:42	Immersed solid with cavitation	#1
shivasluzz Senior Member sluzzer Join Date: Jul 2014 Posts: 142 Rep Power: 11	I am doing a simulation of gear pump with low inlet pressure condition. I use 2 fluids (liquid and vapor) and set saturation pressure to account for the 'cavitation effects'. The solver says 'immersed solid with muliphase combination' is not supported. But the solver runs and converges. Can I use the result or not? In help documentation, it is given that 'mulitphase flow does not properly INTERACT with immersed solid'. Here "INTERACT' means what? I want to check only the reduction in mass flow if cavitation occurs? So can i use the result?

June 9, 2015, 23:10		#6
shivasluzz Senior Member sluzzer Join Date: Jul 2014 Posts: 142 Rep Power: 11	Dynamic remeshing? Is is not same as Mesh displacement? Please share some link or some similar example... Last edited by wyldckat; June 10, 2015 at 15:29. Reason: merge consecutive posts, posted a few minutes apart

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June 5, 2015, 08:05		#2
shivasluzz Senior Member sluzzer Join Date: Jul 2014 Posts: 142 Rep Power: 11	the results are converged to the sufficient accurancy (rms : 1e-6)... i could see the pressure of vapour also.. but there is only one warning during starting that 'Warning: You have used Immersed solids with Mulitphase option. This combination is not supported' Is that solution is totally wrong?

June 6, 2015, 00:47		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	If the fluid cavitates then yes, you results are likely to be completely wrong. Immersed solids cannot account for varying density. But if you do not cavitate or the cavitation volume is small then you might be OK.

June 9, 2015, 10:42		#4
shivasluzz Senior Member sluzzer Join Date: Jul 2014 Posts: 142 Rep Power: 11	Thanks ghorrocks for your reply! Then I think deforming mesh is the only option.. But is it possible to simulate Gear mesh motion?

June 9, 2015, 18:34		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	For a gear pump that will be tricky. the only way it is going to work is with dynamic remeshing.

June 9, 2015, 23:26		#7
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Moving mesh is where the mesh topology remains the same but it is distorted to move. It is only suitable for small ranges of motion. Dynamic remeshing is where moving mesh is used up until the mesh quality drops below a defined criteria, then a remesh is triggered and a new mesh generated and the simulation continues on the new mesh. This obviously involves interaction with the meshing software. I think there are example dynamic remeshing simulations on the ANSYS customer webpage. ANSYS support will also have some I suspect.

December 30, 2021, 08:28		#9
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,827 Rep Power: 27	You can do gear pumps in CFX using the Twinmesh technology (https://www.twinmesh.com/) Alternatively do this in Fluent (or Star-CCM+) using Deforming mesh or Overset-Meshing. All approaches are difficult and require a lot of perseverance. Using Immersed solids is a bad idea. The solids only affect the velocity of the continuous phase, and completely ignore Volume fractions, temperatures, and other scalars. They go though the solids as if there are not there. Therefore, its applicalbility is quite limited. Only use it for a very rough approximation.