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how to apply zero normal pressure gradient boundary on walls
Posted Apr 15, 2011, 2:23 p.m. EDT Version 4.1 1 Reply
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I am trying to simulate a simple lid-driven cavity flow in 2D (sinlge phase laminar flow in a square box). The bottom and two vertical walls are no-slip walls. the top wall is moving in tangent direction at a speed of 1 m/s. I have difficulty in setting boundary conditions for pressure. Pressure point constraint is not approporaite. I want to have zero gradient boundary conditions for pressure for all four walls, which means the normal gradient of pressure is zero. It seems no such boundary condition is available in COMSOL. I tried weak contibution/constraints for boundaries but failed. How to set zero pressure gradient boundaries for walls? should I use weak form? if yes, How to set weak contribution/constraints?
Thanks for your help.
Thanks for your help.
1 Reply Last Post Apr 15, 2011, 4:02 p.m. EDT
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Posted:
1 decade ago
Hi
I'm not sure I catch evrything of what you want to do,
but if you are solving for "p" (a dependent variable) then you have access to the components of its gradient as px,py,pz and second derivatives pxx,pyy,pzz (the latter provided you use at least 2nd order shape functions).
Furthermore, you have the normal direction of the poundaries ...nx,...ny,...nz (here ... is the physics code, i.e. "solid." for solid) and the tangeant boundary vaiables
So woith this you should ahve all your ingredients to build up the weak or "strong" condition at your will and need, no ?
--
Good luck
Ivar
I'm not sure I catch evrything of what you want to do,
but if you are solving for "p" (a dependent variable) then you have access to the components of its gradient as px,py,pz and second derivatives pxx,pyy,pzz (the latter provided you use at least 2nd order shape functions).
Furthermore, you have the normal direction of the poundaries ...nx,...ny,...nz (here ... is the physics code, i.e. "solid." for solid) and the tangeant boundary vaiables
So woith this you should ahve all your ingredients to build up the weak or "strong" condition at your will and need, no ?
--
Good luck
Ivar