
[Sponsors] 
June 16, 2015, 10:38 
LTSInterFoam BC problem

#1 
New Member
xu cong
Join Date: Jun 2015
Posts: 4
Rep Power: 3 
Hello Foamers
I am new to Openfoam and I am doing a simulation about drainage,you can see model I use from the attachment length=5.5m width=3m depth=0.1m The left side is inlet (Q=20 L/s) The right side is outlet and there is a gully on the bottom.(we can assume the gully is the second outlet) The top floor is atmosphere. I used the LTSInterFoam for simulation because I heard this Foam is faster than interFoam.However, I found some very strange result after simulation: 1.As you can see in the attachment, the water cannot get into the gully. 2.The flow rate of inlet is not equal to the flow rate of two outlets. I think it should be the problem of boundary condition, but I don't know which one it is. So I listed my files U/P_pgh/alpha, I hope someone could help me. P_pgh Code:
dimensions [1 1 2 0 0 0 0]; internalField uniform 0; boundaryField { inlet { type buoyantPressure; value uniform 0; } outlet { type zeroGradient; } outlet2 { type zeroGradient; } sides { type buoyantPressure; value uniform 0; } atmosphere { type totalPressure; p0 uniform 0; U U; phi phi; rho rho; psi none; gamma 1; value uniform 0; } lowerwall { type buoyantPressure; value uniform 0; } } Code:
dimensions [0 1 1 0 0 0 0]; internalField uniform (0 0 0); boundaryField { inlet { type flowRateInletVelocity; volumetricFlowRate constant 20e3; rhoInlet 1000; } outlet { type zeroGradient; } outlet2 { type zeroGradient; } sides { type fixedValue; value uniform (0 0 0); } atmosphere { type pressureInletOutletVelocity; value uniform (0 0 0); } lowerwall { type fixedValue; value uniform (0 0 0); } } Code:
dimensions [0 0 0 0 0 0 0]; internalField uniform 0; boundaryField { inlet { type inletOutlet; inletValue uniform 1; value uniform 1; } outlet { type zeroGradient; } sides { type zeroGradient; } atmosphere { type inletOutlet; inletValue uniform 0; value uniform 0; } lowerwall { type zeroGradient; } outlet2 { type zeroGradient; } } Any help would be great, thank you so much! 

June 24, 2015, 09:02 

#2 
Senior Member
Tobias Holzmann
Join Date: Oct 2010
Location: Leoben (Austria)
Posts: 1,555
Blog Entries: 6
Rep Power: 27 
Hi,
Boundary Condition for U
Boundary Condition for alpha
Code:
inlet :: fixedFluxPressure all walls :: fixedFluxPressure outlet :: zeroGradient atmosphere :: depend what you want, I always prefer to set the prghPressureBC
__________________
Best regards, Tobias Holzmann Some interesting OpenFOAM tutorials, publications and videos on www.Holzmanncfd.de OpenFOAM Beginners should check out the new wiki on wiki.openfoam.com A list of some active OpenFOAM contributers can be found »here« A book about the basics of »Mathematics, Numerics, Derivations and OpenFOAM« can be found on www.Holzmanncfd.de 

June 26, 2015, 04:20 

#3 
New Member
xu cong
Join Date: Jun 2015
Posts: 4
Rep Power: 3 
Thank you so much for your kind reply, my model seems better now, but there is still a problem about the velocity in the vertical exit.
The exit is just some fast air flow, the velocity is more than 1000m/s which is obviously wrong, and the pressure is very low. 

June 26, 2015, 04:35 
velocity problem

#4 
New Member
xu cong
Join Date: Jun 2015
Posts: 4
Rep Power: 3 
The simulation is better
but there is a problem with the vertical exit The air speed is super high with a low pressure. Why is that? is it because of the pressure of atmosphere? 

June 29, 2015, 07:48 

#5 
Senior Member
Tobias Holzmann
Join Date: Oct 2010
Location: Leoben (Austria)
Posts: 1,555
Blog Entries: 6
Rep Power: 27 
Hi,
normally you should not ask "why this happens" (: Check your results, and then think about it. For me it seems that you choose a BC configuration that allows you to create a pressure gradient. This gradient will not be compensated with flux, so that a small gradient will always accelerate your flow till infinity or till your solver blow up. Can you share you case?
__________________
Best regards, Tobias Holzmann Some interesting OpenFOAM tutorials, publications and videos on www.Holzmanncfd.de OpenFOAM Beginners should check out the new wiki on wiki.openfoam.com A list of some active OpenFOAM contributers can be found »here« A book about the basics of »Mathematics, Numerics, Derivations and OpenFOAM« can be found on www.Holzmanncfd.de 

June 29, 2015, 08:51 
case

#6 
New Member
xu cong
Join Date: Jun 2015
Posts: 4
Rep Power: 3 
Here is my case.
Thank you for your reply and sorry about my way of asking. It has been over two weeks and I can't solve it so I was a little bit frustrated, sorry about that. 

Tags 
boundary condition, flow rate, multiphase flow 
Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
UDF compiling problem  Wouter  Fluent UDF and Scheme Programming  6  June 6, 2012 04:43 
Gambit  meshing over airfoil wrapping (?) problem  JFDC  FLUENT  1  July 11, 2011 05:59 
natural convection problem for a CHT problem  SeHee  CFX  2  June 10, 2007 06:29 
Adiabatic and Rotating wall (Convection problem)  ParodDav  CFX  5  April 29, 2007 19:13 
Is this problem well posed?  Thomas P. Abraham  Main CFD Forum  5  September 8, 1999 14:52 