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additional unsteady term in URANS

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Old   July 26, 2017, 12:09
Default additional unsteady term in URANS
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Prasun Dutta
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Hi,
I have gone through several research papers and books about Unsteady Reynolds-Averaged Navier–Stokes (URANS) studies and what I understand that in URANS, a time solution of the conventional RANS is performed for 3D unsteady problems, with or without special treatment for the flow instability. The equations of URANS are similar to the RANS models but include the additional unsteady term.
I am using transient k-epsilon (in fluent) model but I am not sure where this extra term was included. I searched in fluent manual and it's still not clear to me. What are the differences in equations (governing / transport equations) when I use transient k-epsilon instead of steady k-epsilon model?
Thnks in adv...
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Old   July 28, 2017, 10:31
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It's just what you wrote, an additional unsteady term is added, one for each equation you are solving (momentum and turbulence variables), and it is treated just like discussed in the manual (solver theory chapter). Basically, for each cell-equation, such addition implies an explicit part which goes on the RHS of the equations solved by Fluent, and an implicit part which goes on the LHS (affecting the matrix diagonal).
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