# gap between the wall and moving piston

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 March 14, 2006, 16:12 gap between the wall and moving piston #1 Nan Guest   Posts: n/a Hi, there, I am simulating the moving piston in a cylinder. But I want the gap between the cylinder wall and the piston as small as possible. Ideally the pistion is sealed. Any suggestions. Thanks a lot.

 March 14, 2006, 16:57 Re: gap between the wall and moving piston #2 Glenn Horrocks Guest   Posts: n/a Hi, What aer you trying to do? Model the flow into piston ring crevices or past the piston rings? Or are you just trying to get a piston to compress the flow? Regards, Glenn Horrocks

 March 14, 2006, 17:26 Re: gap between the wall and moving piston #3 Nan Guest   Posts: n/a Thanks for the response. I just want to see the flow compressed by the piston.

 March 14, 2006, 17:29 Re: gap between the wall and moving piston #4 Nan Guest   Posts: n/a So I don't want the flow bypass through the gap between the wall and the piston.

 March 14, 2006, 18:56 Re: gap between the wall and moving piston #5 Rajit Guest   Posts: n/a Hi Nan, In this case do not leave any gap between the piston and the cylinder(if the gap is small). Just have a look at the moving mesh tutorial ur problem is petty simple.Just move it as a function of time and distance. Thanks Regards Rajit.

 March 14, 2006, 19:10 Re: gap between the wall and moving piston #6 Nan Guest   Posts: n/a Thanks. I will give a try. That means the length of the cylinder wall will be changed automatically? Domain also changed? You mentioned moving mesh tutorial, is that tutorial 20? If it is not, can you tell me which tutorial I should look at. Thanks again.

 March 15, 2006, 02:39 Re: gap between the wall and moving piston #7 Rajit Guest   Posts: n/a Yes both the questions. the wall is moving down compressing the flow. Thanks Regards Rajit

 March 15, 2006, 12:05 Re: gap between the wall and moving piston #8 nan Guest   Posts: n/a Thanks. That is great. If we imagine a rectangular domain, 1 ---------------------- | | 2| |3 | | | | ----------------------- 4 if 4 is moving down, 2 and 3 will become longer automatically. Is my understanding correct? Thanks a lot.

 March 15, 2006, 19:55 Re: gap between the wall and moving piston #9 Rajit Guest   Posts: n/a I could see what you mean.Lets put it this way.If you have a rectangular domain with:- A-Top wall B,C-Side walls D-Bottom wall If we are moving wall A downward then B & C should move along with A with an unspecified motion in the settings. Side walls Should not be stationary when the top wall is moving down and connected to the sides. I hope i have anwsered your question and not confused you Thanks, Regards, Rajit

 April 23, 2011, 04:06 similar problem!!! #10 New Member   Kaustav Join Date: Jul 2010 Posts: 2 Rep Power: 0 I have set up a similar problem with non-newtonian highly viscous fluids at a given temperature. there are two fluids that differ in viscosity by some order of magnitude arranged in a stack to begin with. the top surface is imagined as the bottom of a piston that pushes the assembly down. the two side walls (with no gap between the side walls and the top) are at infinite friction which is closest to real situation. As the piston pushes through, the fluids emerge out from the other end. But, the piston only moves till it reaches the first junction between the two fluids in the stack. then it stops running. Is it possible that the velocity is too low at this point for the piston to overcome the combined effect of the change in viscosity to even higher at that temperature with the effect of the infinite friction at the wall? Should it help to increase the piston velocity at this point? some answer should help.

 April 26, 2011, 22:04 #11 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 13,986 Rep Power: 107 "Then it stops running..." What stops? Any error messages? What happens at that time?

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