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-   -   BFS: steady? (http://www.cfd-online.com/Forums/main/1271-bfs-steady.html)

Jan Ramboer September 9, 1999 11:03

BFS: steady?
 
Hello,

I am solving a backward facing step at a Re=37000. Stepratio=8/9 and inletvelocity= 44.2m/s From the literature I understood this is a steady-state problem. Howver I have problems with convergence solving this with RANS-Baldwin Lomax model. Now I found an article claiming that it isn't steady-state. What is your opinion on this?

Greetings,

Jan R.

John C. Chien September 9, 1999 14:04

Re: BFS: steady?
 
(1). The backward facing step problem is a steady-state problem. (2). Are you using the steady-state formulation or the transient formulation? (3). If you are having the convergence problem with the steady-state formulation, then try to use a more stable first-order scheme to get the converged solution first. From there you can then switch to a high-order method. (4). If you are having the convergence problem with the transient formulation, there is no much you can do, except to use a more smooth mesh, a lower order scheme, and a smaller time step. (5). There could be a feed back effect between the flow field and the turbulence model. So, in this area, you can use a relaxation factor to slow down the change between iterations. (6). It is likely that the method you used is not very stable. This would be the case when using the transient formulation.


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