InterFOAM Pressure Relaxation

Za-ck · March 4, 2014, 04:56

Hi,

if I have a look into the interFOAM code of OpenFOAM 2.2 I can't see the code for the underrelaxation of p_rgh. Normaly, like in pimpleFOAM for example there is a line "p_rgh.relax()" before the momentum corrector.

Nevertheless, the underrelaxation seems to work, because I get different results if I change the factor for p_rgh.

Can someone please explain me, how the relaxation is implemented in interFOAM.

Best regards,

Za-ck

Googlestuff · September 4, 2014, 08:59

I would also like to know how to estimate the relaxation factors for the use in interFOAM. Can anyone give a hint how to do that or give a guess for the values?

Regards,
Googlestuff

Za-ck · September 4, 2014, 11:04

Hi Googlestuff,

the underrelaxation values depend on the case and some other solver settings.

If you are using small timesteps you can run the solver in piso-mode. This means that you have only one outerCorrector(simple loop) loop but at least 2-3 corrector loops (piso loops). In this case you do not necessary need underrelaxation.

If you are running the solver in simple (or pimple) mode you only need one corrector loop but more outerCorrector loops. In this case the solution of the continuity equation is just an approximation and you need underrelaxation. Usally one recommended values like 0.3 for p_rgh and 0.7 for U. It is recommended to use values following the equation 1 = p_rghRelaxation + URelaxation to get fast convergency.

I'don't have any rules for the turbulence or the VOF equation.

I hope that answered your question.

Best,

Za-ck

Googlestuff · September 4, 2014, 12:06

Yes, thank you very much!

March 4, 2014, 04:56	InterFOAM Pressure Relaxation	#1
Za-ck New Member Join Date: Jan 2013 Posts: 17 Rep Power: 13	Hi, if I have a look into the interFOAM code of OpenFOAM 2.2 I can't see the code for the underrelaxation of p_rgh. Normaly, like in pimpleFOAM for example there is a line "p_rgh.relax()" before the momentum corrector. Nevertheless, the underrelaxation seems to work, because I get different results if I change the factor for p_rgh. Can someone please explain me, how the relaxation is implemented in interFOAM. Best regards, Za-ck

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September 4, 2014, 08:59		#2
Googlestuff New Member Sebastian Join Date: Nov 2013 Location: Germany Posts: 14 Rep Power: 12	I would also like to know how to estimate the relaxation factors for the use in interFOAM. Can anyone give a hint how to do that or give a guess for the values? Regards, Googlestuff

September 4, 2014, 11:04		#3
Za-ck New Member Join Date: Jan 2013 Posts: 17 Rep Power: 13	Hi Googlestuff, the underrelaxation values depend on the case and some other solver settings. If you are using small timesteps you can run the solver in piso-mode. This means that you have only one outerCorrector(simple loop) loop but at least 2-3 corrector loops (piso loops). In this case you do not necessary need underrelaxation. If you are running the solver in simple (or pimple) mode you only need one corrector loop but more outerCorrector loops. In this case the solution of the continuity equation is just an approximation and you need underrelaxation. Usally one recommended values like 0.3 for p_rgh and 0.7 for U. It is recommended to use values following the equation 1 = p_rghRelaxation + URelaxation to get fast convergency. I'don't have any rules for the turbulence or the VOF equation. I hope that answered your question. Best, Za-ck

September 4, 2014, 12:06		#4
Googlestuff New Member Sebastian Join Date: Nov 2013 Location: Germany Posts: 14 Rep Power: 12	Yes, thank you very much!