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-   -   Why Fluent does not have 2-order Runge-Kutta scheme? (http://www.cfd-online.com/Forums/fluent/124939-why-fluent-does-not-have-2-order-runge-kutta-scheme.html)

aerosjc October 15, 2013 23:57

Why Fluent does not have 2-order Runge-Kutta scheme?
 
Sometimes we only need a 2-order Runge-Kutta scheme. A 4-order Runge-Kutta maybe give a strange solution.
Anyone knows?

sbaffini October 16, 2013 02:45

Not all numerical schemes are created equal. The 2nd order Runge-Kutta scheme has very different stability properties with respect to the 4th order one. More specifically, its stability region does not cut the imaginary axis, hence it is not well suited for convection dominated problems.

aerosjc October 23, 2013 20:32

But whydoes it have Explicit 2-order Runge-Kutta Time Integration Scheme in the commerical sofaware GASPex, produced by AeroSoft. Inc? Please enlighten me. Thanks :)

sbaffini October 24, 2013 03:12

Well, i didn't say the 2nd order RK scheme is impossible to use, just that it is not well suited for convection dominated flows. If you look at the code page:

http://www.aerosoftinc.com/gasp/features_main.php

you can notice that all the convection schemes are dissipative, hence you can't actually use the code in a way such that the eigenvalues are purely imaginary, which should be enough for the 2nd order scheme to work. I'm just guessing...

aerosjc October 24, 2013 11:18

ok, many thanks! I will read some textbooks to get better understanding.


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