Positive displacement pump moving mesh

eng_norouzi · May 29, 2016, 02:22

I am working on a positive displacement pump (piston pump) using Ansys CFX. The inlet and outlet ports are opened and closed respectively based on the movement of piston. I am using moving mesh for the entire fluid domain. The problem is that when the inlet port is completely closed an error occurs. Therefore always a small gap should exist. How can I remedy this problem? I guess I should use remeshing but I am not familiar with this process.
My case is similar to the movement of internal combustion engine which is a tutorial of CFX. In that example the outlet port is not completely closed. But this does not agree with real condition.
best regards,

ghorrocks · May 29, 2016, 07:29

There are a few possible approaches:

1) Move the valve to almost closed and stop - so never totally close the valve.
2) You can improve option 1 by putting a momentum source term on the valve curtain and when the valve is shut you use a momentum source term to stop flow.
3) You can use an interface which you can slide shut. This allows you to totally shut the valve, but you will have to change the geometry a bit to fit a sliding interface in.
4) You can move the valve to almost shut and then remesh such that you do not mesh the valve curtain so the valve is completely shut. This approach means you shut the valve a little earlier than it should, which can be offset somewhat by modifying the timing at valve closed to give a similar effective flow.

There are probably more options as well. But there is some for you to think about.

May 29, 2016, 02:22	Positive displacement pump moving mesh	#1
eng_norouzi Member ali Join Date: Feb 2011 Posts: 37 Rep Power: 15	I am working on a positive displacement pump (piston pump) using Ansys CFX. The inlet and outlet ports are opened and closed respectively based on the movement of piston. I am using moving mesh for the entire fluid domain. The problem is that when the inlet port is completely closed an error occurs. Therefore always a small gap should exist. How can I remedy this problem? I guess I should use remeshing but I am not familiar with this process. My case is similar to the movement of internal combustion engine which is a tutorial of CFX. In that example the outlet port is not completely closed. But this does not agree with real condition. best regards,

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May 29, 2016, 07:29		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	There are a few possible approaches: 1) Move the valve to almost closed and stop - so never totally close the valve. 2) You can improve option 1 by putting a momentum source term on the valve curtain and when the valve is shut you use a momentum source term to stop flow. 3) You can use an interface which you can slide shut. This allows you to totally shut the valve, but you will have to change the geometry a bit to fit a sliding interface in. 4) You can move the valve to almost shut and then remesh such that you do not mesh the valve curtain so the valve is completely shut. This approach means you shut the valve a little earlier than it should, which can be offset somewhat by modifying the timing at valve closed to give a similar effective flow. There are probably more options as well. But there is some for you to think about.