# Negative Pressure In Fluid Simulation

 Register Blogs Members List Search Today's Posts Mark Forums Read

 February 25, 2011, 23:22 Negative Pressure In Fluid Simulation #1 New Member   zhe rong pan Join Date: Feb 2011 Posts: 2 Rep Power: 0 Hi,All: I'm working on a Euler Fluid Simulator, And I have applied free-slip boundary condition currently by applying the two rules(velocities are zero normal to wall and gradient are zero tangent to wall).But this settings can cause negative pressures. Consider a rectangular block of water falling down and has just hit the ground,all the velocity are pointing downwards and the ground velocity is zero because of free-slip,when solving incompressibility,I get all positive pressures. However,if the above block of water is leaving the ground,that is,all the velocity are pointing upwards and still ground velocity is zero.In this reverse setting, negative pressure is unavoidable. I'm considering modifying free-slip boundary condition:When the velocity is pointing away from the wall,boundary velocity is same as the fluid velocity.When the velocity is pointing to the wall,boundary velocity is zero. But I'm not sure if this will work,or negative pressure is just ok? Could anyone provide some suggestions?

 February 26, 2011, 02:01 #2 New Member   Vasiliy Join Date: Feb 2011 Posts: 9 Rep Power: 8 I think that negative pressure in fluid is ok when velocity flows from the wall. I saw such behaviour in turbomachinery. However it is not so often and can be connected with fact that you use incompressible water. Also you need to check convergence.

 February 26, 2011, 02:28 #3 New Member   zhe rong pan Join Date: Feb 2011 Posts: 2 Rep Power: 0 Thanks for reply,in my system,convergence is always checked to be below 1E-4. But if a block of water that Virtual Contacts the ceiling boundary wall and is starting to fall down,it will be impacted by the negative pressure and deform.Is this an expected phenomenon governed by NS equation?

 Tags negtive, pressure

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post moca CFX 3 September 18, 2010 06:00 Suzzn CFX 18 October 2, 2009 04:18 bioman66 CFX 5 June 3, 2006 01:40 Antech Main CFD Forum 0 April 25, 2006 02:15 AB Siemens 6 November 15, 2004 05:41

All times are GMT -4. The time now is 15:10.