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 miles_davis October 13, 2011 13:16

coding a steady multiphase solver twophaseeulerfoam

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,

 miles_davis October 13, 2011 13:16

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())

1. 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?

1. 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,

 alberto October 14, 2011 20:52

Just a suggestion: do not post the same message multiple times, or you won't receive any answer.

Best,

Alberto

 miles_davis October 15, 2011 19:45

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

 alberto October 15, 2011 19:49

Quote:
 Originally Posted by miles_davis (Post 328059) 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. :-?

 gned June 7, 2016 06:03

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

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