internal field

sinatahmooresi · March 20, 2016, 14:00

Hi friends!
I'm modeling multiphase flow with two phase(water and brine) using openfoam. my question is about the exactly meaning of internal field for "P" ?
because I have a tank that it should be assumed with water and then a jet of brine is entering the tank. so internal field of p had a hydrostatic distribution I as it seems. but I think my imagination of this internal field is wrong .
all the best

TobM · March 21, 2016, 03:59

p is calculated from the solver in OpenFOAM multiphase solvers. You define p_rgh which is the pressure minus hydrostatic pressure: p_rgh = p - rho*g*h
This enables you to define a simple constant pressure boundary condition over different fluids and fluid heights.

sinatahmooresi · March 30, 2016, 09:56

dear TobM!
so that mean when I have a tank with water that is not exactly full of water( there is free surface of air ) I should assign atmosphere pressure for this internal field ? is the condition of this part of OpenFOAM like "operating conditions" in FLUENT ?
thank u for your guidance
all the best

TobM · March 30, 2016, 10:11

The last time I used Fluent was a few years ago...
From your words "free surface" I think you are using interFoam solver, right?
Just look into the tutorials of the solver and look up the boundary conditions used in those.
for walls p_rgh has to be fixedFluxPressure, for inlets/outlets you can use for example totalPressure BCs, or depending on your problem fixedValue.
Yes you can set the pressure to "atmosphere pressure" for both water and air.

sinatahmooresi · March 31, 2016, 07:03

i actually didn't run the model yet! because I'm beginner in Foam. i want to model a jet of brine that exit from a nozzle in bottom of a tank of water(ambient fluid). i have two choice for choosing the solver. one way is use directly one of the multiphase solvers of OpenFOAM. second one is using one of incompressible solvers with some modifications like pisoFoam. by first choice i dont know really which one of them is the best, i guess that "twophaseEulerFoam" could be . or maybe "two LiquidMixingFoam" but i think the first one is better. because i checked their tutorials and i found "bubbleColumn" in "twophaseEulerFoam" and "lockExchange" in "twoLiquidMixingFoam" . so my simulation i think is resemble with bubble columns more than something like lockExchange problem . so that is all ! i'm studying to find out which one is better
thanks for your guidance

sinatahmooresi · April 2, 2016, 12:42

also there is an another question about my project!
i told u that i have two choice in my last reply to thread. and i don't talked about my selection with "pisoFoam". i set the model and geometry with k-e for turbulence modeling. i also modified pisoFoam solver for calculating T and C scalar field. and when i run the model. it stops at reading epsilon from "0' directory. and the error is :
Cannot find patchField entry for INLET

i should say that the inlet is set with "patch" B.C in boundary file. INLET is the entrance of my tank .

March 20, 2016, 14:00	internal field	#1
sinatahmooresi Senior Member CFD_Lovers Join Date: Mar 2015 Posts: 168 Rep Power: 11	Hi friends! I'm modeling multiphase flow with two phase(water and brine) using openfoam. my question is about the exactly meaning of internal field for "P" ? because I have a tank that it should be assumed with water and then a jet of brine is entering the tank. so internal field of p had a hydrostatic distribution I as it seems. but I think my imagination of this internal field is wrong . all the best

March 31, 2016, 07:03		#5
sinatahmooresi Senior Member CFD_Lovers Join Date: Mar 2015 Posts: 168 Rep Power: 11	i actually didn't run the model yet! because I'm beginner in Foam. i want to model a jet of brine that exit from a nozzle in bottom of a tank of water(ambient fluid). i have two choice for choosing the solver. one way is use directly one of the multiphase solvers of OpenFOAM. second one is using one of incompressible solvers with some modifications like pisoFoam. by first choice i dont know really which one of them is the best, i guess that "twophaseEulerFoam" could be . or maybe "two LiquidMixingFoam" but i think the first one is better. because i checked their tutorials and i found "bubbleColumn" in "twophaseEulerFoam" and "lockExchange" in "twoLiquidMixingFoam" . so my simulation i think is resemble with bubble columns more than something like lockExchange problem . so that is all ! i'm studying to find out which one is better thanks for your guidance Last edited by sinatahmooresi; March 31, 2016 at 12:36.

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March 21, 2016, 03:59		#2
TobM Member Join Date: Sep 2014 Location: Germany Posts: 88 Rep Power: 12	p is calculated from the solver in OpenFOAM multiphase solvers. You define p_rgh which is the pressure minus hydrostatic pressure: p_rgh = p - rhogh This enables you to define a simple constant pressure boundary condition over different fluids and fluid heights.

March 30, 2016, 09:56		#3
sinatahmooresi Senior Member CFD_Lovers Join Date: Mar 2015 Posts: 168 Rep Power: 11	dear TobM! so that mean when I have a tank with water that is not exactly full of water( there is free surface of air ) I should assign atmosphere pressure for this internal field ? is the condition of this part of OpenFOAM like "operating conditions" in FLUENT ? thank u for your guidance all the best

March 30, 2016, 10:11		#4
TobM Member Join Date: Sep 2014 Location: Germany Posts: 88 Rep Power: 12	The last time I used Fluent was a few years ago... From your words "free surface" I think you are using interFoam solver, right? Just look into the tutorials of the solver and look up the boundary conditions used in those. for walls p_rgh has to be fixedFluxPressure, for inlets/outlets you can use for example totalPressure BCs, or depending on your problem fixedValue. Yes you can set the pressure to "atmosphere pressure" for both water and air.

April 2, 2016, 12:42		#6
sinatahmooresi Senior Member CFD_Lovers Join Date: Mar 2015 Posts: 168 Rep Power: 11	also there is an another question about my project! i told u that i have two choice in my last reply to thread. and i don't talked about my selection with "pisoFoam". i set the model and geometry with k-e for turbulence modeling. i also modified pisoFoam solver for calculating T and C scalar field. and when i run the model. it stops at reading epsilon from "0' directory. and the error is : Cannot find patchField entry for INLET i should say that the inlet is set with "patch" B.C in boundary file. INLET is the entrance of my tank .