how to improve time step

send1000 · September 3, 2011, 13:41

I am trying to use SIMPLE algorithm to simulate a 2D flow in micro rectangle pipe. I set up the constant pressure values as inlet and outlet boundary condition and two side is no slip wall. The large scale differences between pressure and size of the pipe leads to the results that it converges only if the step time is very very small(10e-9s). Who could tell me how to do if I want to improve step time to 1s~0.001s?

alberto · September 6, 2011, 22:11

If you use simpleFoam to deal with an unsteady problem, this is not correct. You should use pisoFoam or pimpleFoam.

If you use pimpleFoam, you can use larger time steps using under-relaxation and outer correctors (under-relaxation is not appropriate in pisoFoam).

send1000 · September 7, 2011, 16:00

Thank you very much , alberto

Do you know where I can find the details about Pimple method? I am programming now by myself and I need make sure every details.

Thank you again.

alberto · September 7, 2011, 21:06

I am not aware of references about it. You can take a look at pimpleFoam to see how it is implemented.

September 3, 2011, 13:41	how to improve time step	#1
send1000 New Member Join Date: Jul 2011 Posts: 4 Rep Power: 14	I am trying to use SIMPLE algorithm to simulate a 2D flow in micro rectangle pipe. I set up the constant pressure values as inlet and outlet boundary condition and two side is no slip wall. The large scale differences between pressure and size of the pipe leads to the results that it converges only if the step time is very very small(10e-9s). Who could tell me how to do if I want to improve step time to 1s~0.001s?

September 6, 2011, 22:11		#2
alberto Senior Member Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,912 Rep Power: 36	If you use simpleFoam to deal with an unsteady problem, this is not correct. You should use pisoFoam or pimpleFoam. If you use pimpleFoam, you can use larger time steps using under-relaxation and outer correctors (under-relaxation is not appropriate in pisoFoam). __________________ 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.

September 7, 2011, 21:06		#4
alberto Senior Member Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,912 Rep Power: 36	I am not aware of references about it. You can take a look at pimpleFoam to see how it is implemented. __________________ 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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September 7, 2011, 16:00		#3
send1000 New Member Join Date: Jul 2011 Posts: 4 Rep Power: 14	Thank you very much , alberto Do you know where I can find the details about Pimple method? I am programming now by myself and I need make sure every details. Thank you again.