relaxation factor for PISO algorithm

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 January 30, 2013, 17:48 relaxation factor for PISO algorithm #1 Senior Member   Sasan Ghomi Join Date: Sep 2012 Location: Iran - Tehran Posts: 187 Rep Power: 7 Hi every body, I have a question about relaxation factor : sonicTurbDymEngineFoam is a transient solver for compressible flow with mesh motion.(OP-1.6-ext) It uses PISO algoritm for solving equations.when I use relaxation factor in a case with this solver I get correct result.Do you think using of relaxation factor in PISO algorithm is wrong??? why??? In a header file of the source code of this solver I saw this code : Code: `UEqn.relax();` thanks, Sasan.

February 2, 2013, 06:51
#2
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Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
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In order to give a bump to this thread, here's what I answered Sasan the other day, through private messaging:
Quote:
Originally Posted by wyldckat
Hi Sasan,

I don't know much about this. All I know is:
1. Both PISO and SIMPLE can be used for transient simulations.
2. PISO algorithm is described here: http://openfoamwiki.net/index.php/Th...hm_in_OpenFOAM
3. SIMPLE algorithm is described here:http://openfoamwiki.net/index.php/Th...hm_in_OpenFOAM
4. Then there is PIMPLE, which is a mix of PISO+SIMPLE... and I quote:
Quote:
 Originally Posted by alberto PISO simply does not iterate over the equations: it solves alpha, Theta, U, p, k, epsilon and proceeds in time. PIMPLE is a combination of PISO and SIMPLE. In other words you can have outer correctors, if you set the appropriate keyword in the fvSolution PIMPLE sub-dictionary.
Therefore, the relaxation factors you're talking about may depend on whether you're using PISO or PIMPLE.

You might have gotten a better answer if you had asked in the public forum...

Best regards,
Bruno
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