How to choose end time for a steady state problem

mecbe2002 · March 5, 2010, 02:46

Hi,

I am using "rhopSonicFoam" solver for solving 3d steady inviscid flow around ONERA M6 wing. How to decide the end time?

Ma=0.84, alpha=3.04
Properties of air R-287.05 J/kgK, gamma-1.4, T-255.6K

Computational domain size is 11m x 5m x 10m (Hexahedral).
No.of cells = 341797
time step = 5e-07

djbungee · March 5, 2010, 05:54

Hi,

that is an interesting question. My suggestion is that you observe the development of the initial residuals for every equation for the cycles ('time' steps).

If you have sufficient (computation) time and perform this (kind of) simulation or case setup for the first time, I would suggest you do the simulation as long as possible to get an idea of how the residuals develop over computation time (and how low they can go) and try to find a suitable optimum for quality of results (i.e. reduction of change in residual for every cycle - which is not always the same

) and computational effort (time).

So, unfortunately, no general guideline available ...

Best regards, Ulf.

alberto · March 25, 2010, 21:49

You can additionally track the evolution of which you know the behaviour, and check when it stops evolving.

It is always a good idea to add a "physical" convergence criterion to the one based on residuals.

Best,

March 5, 2010, 02:46	How to choose end time for a steady state problem	#1
mecbe2002 Senior Member KGN Join Date: Oct 2009 Location: Chennai, India Posts: 121 Rep Power: 16	Hi, I am using "rhopSonicFoam" solver for solving 3d steady inviscid flow around ONERA M6 wing. How to decide the end time? Ma=0.84, alpha=3.04 Properties of air R-287.05 J/kgK, gamma-1.4, T-255.6K Computational domain size is 11m x 5m x 10m (Hexahedral). No.of cells = 341797 time step = 5e-07

March 25, 2010, 21:49		#3
alberto Senior Member Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,912 Rep Power: 36	You can additionally track the evolution of which you know the behaviour, and check when it stops evolving. It is always a good idea to add a "physical" convergence criterion to the one based on residuals. Best, __________________ 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.

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March 5, 2010, 05:54		#2
djbungee Member Ulf Bunge Join Date: Mar 2009 Location: Wolfsburg, Germany Posts: 34 Rep Power: 17	Hi, that is an interesting question. My suggestion is that you observe the development of the initial residuals for every equation for the cycles ('time' steps). If you have sufficient (computation) time and perform this (kind of) simulation or case setup for the first time, I would suggest you do the simulation as long as possible to get an idea of how the residuals develop over computation time (and how low they can go) and try to find a suitable optimum for quality of results (i.e. reduction of change in residual for every cycle - which is not always the same ) and computational effort (time). So, unfortunately, no general guideline available ... Best regards, Ulf.