# coding a steady multiphase solver twophaseeulerfoam

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 October 13, 2011, 13:16 coding a steady multiphase solver twophaseeulerfoam #1 Member   Miles Join Date: Sep 2011 Posts: 48 Rep Power: 13 Hi, I am using the twophaseeeulerfoam solver to simulate air bubbles in water. I want to have a steady state version of the solver. Solution1 According to what I have read, I should first try to under-relax the resolution and raise the time step. I do not understand why? In fact I do not understand the role of under-relaxtion factor in an unsteady solver. Does anyone have a point on the subject or some documentation of the relaxation process in Openfoam (and in general, reading is never bad!)? This could help me to understand. Solution2 On the other hand if I want to change the solver to be steady witch library I was thinking to do so - Remove time dependence in the solver - Change the vel-press scheme (I was thinking using simple scheme) - Modify the fvsol and fvscheme dict. Does this seem correct? Does this seem an affordable task for an OF newbee? Thanks for your opinions and help. Regards,

 October 13, 2011, 13:16 #2 Member   Miles Join Date: Sep 2011 Posts: 48 Rep Power: 13 Hi I have tried the first solution but it seems that putting a subdict for relaxation at the end of fvSolution has no effect. I am not sure if it is taken into account. So I switched to the coding of a steady twophaseeluerfoam solver. I am tryning to understand how the solver is coded. I have a few questions and my sorry in advance if it seems to easy but my C++ is very bad. 1.fvVectorMatrix UbEqn(Ub, Ub.dimensions()*dimVol/dimTime) Is it possible to modify the definition of fvVectorMatrix like that: fvVectorMatrix UbEqn(Ub, Ub.dimensions()) volScalarField rUaA(1.0/UaEqn.A()) I do not understand what is done here. What is the definition and the purpose of rUaA and UaEqn.A() ? Is this related to the first guess on momentum equation in the PIMPLE algorithm? Ua = rUaA*UaEqn.H() Same question for UaEqn.H() 4. DDTU.h What is the purpose of having a special file for the equation on UA and UB? Can it be included in my SIMPLE loop -since I will move the scheme from pimple to simple. Thanks for any help. Regards,

 October 14, 2011, 20:52 #3 Senior Member   Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,912 Rep Power: 35 Just a suggestion: do not post the same message multiple times, or you won't receive any answer. Best, Alberto __________________ Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats (current status: http://albertopassalacqua.com/?p=1541) OpenQBMM - An open-source implementation of quadrature-based moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using.

 October 15, 2011, 19:45 #4 Member   Miles Join Date: Sep 2011 Posts: 48 Rep Power: 13 Sorry for that That was not my intention. I wanted to move the thread to the proper section and delete the older. But I did'nt manage to find how to delete a thread... orry again. Miles

October 15, 2011, 19:49
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Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,912
Rep Power: 35
Quote:
 Originally Posted by miles_davis Sorry for that That was not my intention. I wanted to move the thread to the proper section and delete the older. But I did'nt manage to find how to delete a thread... orry again. Miles
Ooops, I did not pay attention to the sections Sorry. I answered in the other thread.

I don't know if it's possible to delete a thread without administrative rights. :-?
__________________
Alberto Passalacqua

GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats (current status: http://albertopassalacqua.com/?p=1541)
OpenQBMM - An open-source implementation of quadrature-based moment methods.

To obtain more accurate answers, please specify the version of OpenFOAM you are using.

 June 7, 2016, 06:03 #6 New Member   gned Join Date: Oct 2012 Posts: 18 Rep Power: 12 dear Alberto, as you expert of multiphase flows, if i have this case with, let's take, very simple geometry as a common pitzDaily nozzle with incompressible flow inside but which then really separates at the sharp corner so that, contrary to this usual picture where after the corner a vortex filled of liquid forms, we have really a void not-wetted stagnant zone. https://www.dropbox.com/s/8g5lsjydba2nhk0/pitz.png?dl=0 As the free-surface (in corrispondence of which we have a sharp change into the fluid density from rho to 0) detaching is unknown a priori, which solver to use in OF to find the solution? An incompressible solver will put at best, at the beginning, a stagnant pocket there but of fluid, and so unstable because with time this zone wil be filled with vorticity (also I find absolute negative pressure inside it). A compressible solver would solve an equation of state at the dead zone but actually rho=0 there (I fear to have continuity problems). So an interFoam maybe with a rho -> 0 (indeed I would like to find the solution with still no cavitation occurs, i.e. with the dead zone not still vapour-filled through an interPhase ChangeFoam but really void enveloped by separated flow) ? Or I must program some changes in a solver, what you suggest ? Thank you really much

 February 6, 2019, 16:25 Converting twoPhaseEulerFoam into steady state solver using fvoptions #7 Member   Join Date: Apr 2016 Posts: 30 Rep Power: 9 Hi all, I have been following this thread and I would like to ask if there is another way to convert twoPhaseEulerFoam into a steady state solver. fvSchemes has a option called ddt schemes. Code: ```ddtSchemes { default steadyState; }``` Using steadyState as a ddt scheme basically mean that the ddt term in the equations is zero. In that situation how are the rest of the terms of the equations calculated and would that constitute a steady state solver or can certain additions be done to make it a steady state solver? Thanks and Regards, Shantanu

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