# inlet boundary condition based on specified water level

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

 August 28, 2013, 15:37 inlet boundary condition based on specified water level #1 Member   Hale Join Date: May 2013 Posts: 53 Rep Power: 6 Hi, I am dealing with a two phase flow problem where I need to specify a constant water level for the inlet. I do not want to do it by specifying a velocity or flux. I tried to do it by specifying a hydrostatic pressure (rho*g*h) for p_rgh and zeroGradient for U but it blows up! Is there any way to specify the height of the water at the inlet? Thanks Hale

 August 29, 2013, 14:30 #2 Senior Member   Nima Samkhaniani Join Date: Sep 2009 Location: Tehran, Iran Posts: 1,215 Blog Entries: 1 Rep Power: 17 well i guess you can do it via non-uniform alpha1 (i assumed you use interFoam as solver ) __________________ Telegram channel (https://telegram.me/openfoam4Iranian) My Weblog in Persian(http://openfoam.blogfa.com/) My Personal Website (http://nimasamkhaniani.ir/)

August 30, 2013, 03:53
#3
Member

Hale
Join Date: May 2013
Posts: 53
Rep Power: 6
Quote:
 Originally Posted by nimasam well i guess you can do it via non-uniform alpha1 (i assumed you use interFoam as solver )
Hi Nima,

Thanks for the reply. Yes, I use interFoam. For the inlet where I need a constant water level I have defined alpha1=1 and zeroGradient for everwhere else. What did you mean with non-uniform alpha1?

August 30, 2013, 04:05
#4
Senior Member

Nima Samkhaniani
Join Date: Sep 2009
Location: Tehran, Iran
Posts: 1,215
Blog Entries: 1
Rep Power: 17
well you can put a non-uniform alpha
something similar this :
Quote:
 y < h ? 1 : 0
where h is water level

you can used:

1- code stream
2: groovyBC

to create such nonuniform BC
__________________
Telegram channel (https://telegram.me/openfoam4Iranian)
My Personal Website (http://nimasamkhaniani.ir/)

 August 30, 2013, 04:16 #5 Member   Hale Join Date: May 2013 Posts: 53 Rep Power: 6 This is too complicated for me but would you please explain what will this non-uniform alpha1 do? I need a uniform water level at the inlet so why should I changed alpha1 to non-uniform?

 August 30, 2013, 04:41 #6 Senior Member   Nima Samkhaniani Join Date: Sep 2009 Location: Tehran, Iran Posts: 1,215 Blog Entries: 1 Rep Power: 17 in your post #1, you said you want a constant water level!, so i assumed! a portion of your inlet fill with water! if the whole inlet is water! then specify the velocity or flux whats wrong then? __________________ Telegram channel (https://telegram.me/openfoam4Iranian) My Weblog in Persian(http://openfoam.blogfa.com/) My Personal Website (http://nimasamkhaniani.ir/)

 August 30, 2013, 09:52 #7 Member   Hale Join Date: May 2013 Posts: 53 Rep Power: 6 The problem is that I'm simulating a real life problem where the flux is not known but the water level can be adjusted. Therefore I want to specify the water level in terms of hydrostatic pressure or something else that can allow the model to find the flux/velocity by itself.

 April 10, 2014, 11:18 Different water levels; BCs OpenFOAM #8 New Member   Join Date: Apr 2014 Posts: 3 Rep Power: 5 I have a similar problem. I have two water tanks connected by a pipe. The tanks have two different water levels. I want to keep this difference constant but I do not know the flow rate at the inlet and outlet. Therefore I should find the BCs that allows me to keep the water levels constant in the tanks. Any help? Thank you

 December 22, 2016, 05:10 #9 New Member   Tinu Join Date: Nov 2016 Posts: 11 Rep Power: 2 I have a very similar problem for open channel flows What I need is an upstream boundary that physically behaves like there would be an unlimited reservoir of water with a fixed water level and no prescribed flow rate / velocity at the boundary. Velocity at the upstream boundary should develop as a consequence of the velocities in the model. I have tried to fix upstream water level with groovyBC: Upstream BC ------------------ alpha.water: pos().z <= waterlevel ? 1:0 U: zeroGradient p_rgh: fixedFluxPressure Downstream BC (simulating free outflow) ------------------- alpha.water: inletOutlet, inletValue uniform 0; U: pressureInletOutletVelocity p_rgh: totalPressure p0 uniform 0; Atmosphere ---------------------- alpha.water: inletOutlet, inletValue uniform 0; U: pressureInletOutletVelocity p_rgh: totalPressure p0 uniform 0; These BC seem to work nicely with a very simple rectangular open channel flow. With more complicated meshes the simulation seemed to blow up, developing unphysical pressure/velocity from one point near the fixed inlet water level. I suspect the combination of zeroGradient for U and fixedFluxPressure for p_rgh at inlet is not stable. Any ideas which combinations for p_rgh and U could work when fixing the inlet alpha.water level with groovyBC? Hints are highly welcome! Tinu Bashar likes this.

February 15, 2017, 22:14
#10
Member

Bashar
Join Date: Jul 2015
Posts: 63
Rep Power: 3
Quote:
 Originally Posted by tinu80 I have a very similar problem for open channel flows What I need is an upstream boundary that physically behaves like there would be an unlimited reservoir of water with a fixed water level and no prescribed flow rate / velocity at the boundary. Velocity at the upstream boundary should develop as a consequence of the velocities in the model. I have tried to fix upstream water level with groovyBC: Upstream BC ------------------ alpha.water: pos().z <= waterlevel ? 1:0 U: zeroGradient p_rgh: fixedFluxPressure Downstream BC (simulating free outflow) ------------------- alpha.water: inletOutlet, inletValue uniform 0; U: pressureInletOutletVelocity p_rgh: totalPressure p0 uniform 0; Atmosphere ---------------------- alpha.water: inletOutlet, inletValue uniform 0; U: pressureInletOutletVelocity p_rgh: totalPressure p0 uniform 0; These BC seem to work nicely with a very simple rectangular open channel flow. With more complicated meshes the simulation seemed to blow up, developing unphysical pressure/velocity from one point near the fixed inlet water level. I suspect the combination of zeroGradient for U and fixedFluxPressure for p_rgh at inlet is not stable. Any ideas which combinations for p_rgh and U could work when fixing the inlet alpha.water level with groovyBC? Hints are highly welcome! Tinu

Thanks for sharing the BC.I am simulating flow past plate with free surface.I will try your BC.

Sent from my iPhone using CFD Online Forum mobile app

 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 yosuke1984 OpenFOAM Verification & Validation 3 May 6, 2015 06:16 Mavier CFX 5 April 29, 2013 00:00 Clementhuon OpenFOAM Native Meshers: snappyHexMesh and Others 6 March 12, 2012 13:41 Chander CFX 3 March 11, 2012 22:18 sogolf FLUENT 0 September 27, 2009 15:05

All times are GMT -4. The time now is 10:31.