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Compression and Pressure Volume Diagram

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Old   December 31, 2010, 05:01
Question Compression and Pressure Volume Diagram
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Hi Guys,

I have two question and firs of all i explain my study. It is a 2D dynamic simulation of compression chamber and valve. I gave the images respectively of crank angle. At first image, valve closed and decompression started. At second image, valve opened and at the top. At third image, valve just started to close. Then after one degree of crank angle suddenly static pressure contour is destroyed. As if fluent split the cell zones. Pressure distribution is important for me during the closing of valve. Why its hapening and how can i observe closing of valve?

My second question is about pressure volume diagram. Can FLUENT plot the pressure volume diagram of compression and how?

Best regards and thanks in advance..
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Old   January 3, 2011, 05:50
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Old   January 3, 2011, 06:02
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Quote:
Originally Posted by chshaini View Post
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P-V diagram is very urgent

非常感谢
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Old   January 6, 2011, 10:06
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something is weird
Ca you post a picture (actually same as your 2nd picture) with a zoom on the white lane at the extremity of your piston
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Old   January 6, 2011, 11:00
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Thank you for your interest..

Valve opens at 45[deg] of crank angle and started to close 70[deg]. After 70 [deg] above and belove of the valve cells like splitted and problem doesn't converge.
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Old   January 7, 2011, 05:37
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ok it seems you have interfaces working well till crack angle 75°
Then the interfaces aren't working anymore since they seem t be treated as wall.
Can you repost the 2 last pictures with mesh
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Old   January 7, 2011, 06:01
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Good point you're right. In boundary conditions interfaces turned to wall after 70°. Why?
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Old   January 7, 2011, 06:56
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Did you set any event?
define/dynamic-mesh/events...
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Old   January 7, 2011, 07:40
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Yes i use "Create/Delete Sliding Interfaces" and "Deactivate/Activate Cell Zone".

Actually i use "Deactivate/Activate Cell Zone" for prevent the leakage between the valve and plate. I cant use truly the minimum valve lift. I also expect an advice about minimum valve lift.

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Old   January 7, 2011, 08:02
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As events are linked with time, check at which time appears this error, and compare with the time you gave in the event
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Old   January 7, 2011, 08:15
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It appears when "delete sliding interface" event become active.
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Old   January 7, 2011, 08:17
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why do you want them to delete?
If you delete them, then Fluent understands wall... and this is what you get
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Old   January 7, 2011, 10:00
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I take the studentFLUENT - SI Engine Tutorial as reference. It dosen't happen in tutorial but you're right, that event delete the interfaces. I wont use it.. Thank you for your interest. So what about p-v diagram?
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Old   January 7, 2011, 10:18
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p-v diagramm:
you can try something with plot/xy-Plot, but not sure you can pick something else as a lenth for x-axis
Else you write what you want in files, and handle your stuff with excel, gnuplot etc...
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Old   January 7, 2011, 10:24
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i'll try it. thanks i'm grateful to you.
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Old   January 14, 2011, 10:02
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Hi guys it's me again,

With your help my simulations are almost issueless. I think i have leakage problem near the valves. As it can be seen in stream function and mass flow rate over the interfaces near the valves when the valves closed. The mass flow rate over the interfaces is equal the mass flow inlet value.

There are only a range of cell between the valve and plate. The cells height is 0.005 mm. I use 0.006mm as minimum valve lift in IC DM Parameters.

How can i define the valves as leakproof?
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Old   January 14, 2011, 10:23
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You can enforce the leakfree valve by using an event: switch the interface BC as wall at special time
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Old   January 14, 2011, 11:13
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Thank you max but your suggestion is break down the dynamic mesh process and fluent received a fatal signal. I couldn't understand what exactly the minimum valve lift and how can i use it?
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Old   January 17, 2011, 02:31
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From Online-Help:
"FLUENT assumes that once you have set up the mesh topology, the mesh topology is unchanged throughout the entire simulation. Therefore, FLUENT does not allow you to completely close the valves such that the cells between the valve and the valve seat become degenerate (flat cells) when these surfaces come in contact (removing these flat cells would require the creation of new boundary face zones). To prevent the collapse, you need to define a minimum valve lift and FLUENT will automatically stop the motion of the valve when the valve lift is smaller than the minimum valve lift value. The minimum valve lift value can be specified in the Dynamic Mesh Parameters panel. For the current example, a minimum valve lift value of 0.1 mm is assumed.

When the valve position is smaller than the minimum valve lift value, it is normal practice to assume that the valve is closed. The actual closing of the valves is accomplished by deleting the sliding interfaces that connect the chamber cell zone to the dynamic layering zones on the valves. The interface zones are then converted to walls to close off the "gaps'' between the valves and the valve seats. The valve opening is achieved by the reverse process. When the valve lift has reached beyond the minimum valve lift value, the valve is assumed to be open and you can redefine the sliding interfaces such that the chamber zone is now connected to the dynamic layering zones above the valves."
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