Close Domain - Engine Valve

Alessio · January 20, 2010, 09:35

Hi,
I’m trying to close a domain during a transient simulation with ANSYS CFX but I have some problems, such as a negative volume.
The problem is similar to an engine valve; during the simulation, the valve can be open or close, following a displacement function and the fluid must be stopped when the valve is close.
I’ve chosen the Mesh Motion Option, but it doesn’t work when two surface are in contact and the fluid domain is close.
Is it possible with ANSYS CFX 12.0 to close a domain during the simulation?
The only tutorial about Mesh Motion (Fluid Structure Interaction and Mesh Deformation) doesn’t explain this problem.
In this forum, I haven't found anything about my problem.

Many thanks to all,

Alessio

ghorrocks · January 20, 2010, 16:13

In V12 the expected way to model a poppet valve shutting is to use mesh motion until the mesh becomes too distorted and then interpolate onto a new grid to continue the motion. When the valve is almost shut you then interpolate onto a new mesh with the valve completely shut, so a gap exists between the port and the cylinder.

You can also model the valve as an immersed solid and then you don't have any of these problems but boundary layer resolution on the valve is not so good.

Alessio · January 21, 2010, 11:11

Many thanks Glenn

I'll find information about it. I think you are speaking about "remeshing" and "interpolating mesh".

In the tutorials, there isn't anything. Can you indicate me some references about this problem?

Thanks,

Alessio

Tristan · January 21, 2010, 12:46

Alessio,

I asked Ansys support a while back for more information about remeshing and they gave me a powerpoint presentation entitled "Multi-Configuration and Remeshing Capabilities in CFX R12.0". I don't know if the material in this presentation made it into a tutorial for CFX 12.1 because I haven't upgraded yet but it contains a pressure-relief valve example with remeshing that would be relevant to your problem. You should contact Ansys support and ask them to give it to you.

Tristan

ckleanth · January 21, 2010, 18:20

in addition what the others said you will probably find that at the moment the immersed solid cababilities of cfx are not that great function especialy when it is to model poppet valves where proper wall functions are important (you can search this forum to find why) and second you will need ICEM lisences (or if you are clever you can use your own meshing code) in order to remesh the geomerty. at the moment fluent is much more suitable for engine simulations if you can still choose a cfd solver.

Alessio · January 22, 2010, 03:34

Thanks to all!

I know Fluent and I think that it's better than CFX for the Internal Combustion Engine but I'd like to try also with CFX!

I'll contact ANSYS support for the presentation "Multi-Configuration and Remeshing Capabilities in CFX R12.0" (thanks @ Tristan)
Moreover, I've found in this forum that there're two tutorials:
1. IC Engine
2. Valve Motion
These tutorials aren't introduced in ANSYS V12, so I'll ask they to ANSYS support.

Thanks,
Alessio

January 20, 2010, 09:35	Close Domain - Engine Valve	#1
Alessio New Member Alessio Simi Join Date: Jan 2010 Posts: 3 Rep Power: 16	Hi, I’m trying to close a domain during a transient simulation with ANSYS CFX but I have some problems, such as a negative volume. The problem is similar to an engine valve; during the simulation, the valve can be open or close, following a displacement function and the fluid must be stopped when the valve is close. I’ve chosen the Mesh Motion Option, but it doesn’t work when two surface are in contact and the fluid domain is close. Is it possible with ANSYS CFX 12.0 to close a domain during the simulation? The only tutorial about Mesh Motion (Fluid Structure Interaction and Mesh Deformation) doesn’t explain this problem. In this forum, I haven't found anything about my problem. Many thanks to all, Alessio

January 21, 2010, 18:20		#5
ckleanth Senior Member George Join Date: Mar 2009 Location: Birmingham, UK Posts: 257 Rep Power: 18	in addition what the others said you will probably find that at the moment the immersed solid cababilities of cfx are not that great function especialy when it is to model poppet valves where proper wall functions are important (you can search this forum to find why) and second you will need ICEM lisences (or if you are clever you can use your own meshing code) in order to remesh the geomerty. at the moment fluent is much more suitable for engine simulations if you can still choose a cfd solver. __________________ Top 4 tips 1. Knowledge is everything and Ignorance is dangerous. 2. Understand your limitations and try to eliminate them. 3. Get yerself a bike and hoon the chuffer. You will soon learn why dogs like to hang their heads out the car window. 4. Please before asking any questions on how to run simulations in CFX, go though all the tutorials

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January 20, 2010, 16:13		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	In V12 the expected way to model a poppet valve shutting is to use mesh motion until the mesh becomes too distorted and then interpolate onto a new grid to continue the motion. When the valve is almost shut you then interpolate onto a new mesh with the valve completely shut, so a gap exists between the port and the cylinder. You can also model the valve as an immersed solid and then you don't have any of these problems but boundary layer resolution on the valve is not so good.

January 21, 2010, 11:11		#3
Alessio New Member Alessio Simi Join Date: Jan 2010 Posts: 3 Rep Power: 16	Many thanks Glenn I'll find information about it. I think you are speaking about "remeshing" and "interpolating mesh". In the tutorials, there isn't anything. Can you indicate me some references about this problem? Thanks, Alessio

January 21, 2010, 12:46		#4
Tristan Member Tristan Burton Join Date: Mar 2009 Posts: 43 Rep Power: 17	Alessio, I asked Ansys support a while back for more information about remeshing and they gave me a powerpoint presentation entitled "Multi-Configuration and Remeshing Capabilities in CFX R12.0". I don't know if the material in this presentation made it into a tutorial for CFX 12.1 because I haven't upgraded yet but it contains a pressure-relief valve example with remeshing that would be relevant to your problem. You should contact Ansys support and ask them to give it to you. Tristan

January 22, 2010, 03:34		#6
Alessio New Member Alessio Simi Join Date: Jan 2010 Posts: 3 Rep Power: 16	Thanks to all! I know Fluent and I think that it's better than CFX for the Internal Combustion Engine but I'd like to try also with CFX! I'll contact ANSYS support for the presentation "Multi-Configuration and Remeshing Capabilities in CFX R12.0" (thanks @ Tristan) Moreover, I've found in this forum that there're two tutorials: 1. IC Engine 2. Valve Motion These tutorials aren't introduced in ANSYS V12, so I'll ask they to ANSYS support. Thanks, Alessio