# Numeca Fine

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 June 5, 2001, 04:22 Numeca Fine #1 dimitris Guest   Posts: n/a Hi I was wandering if anybody knows why when running a problem with prescribed mass flow in inlet and outlet leads to divergence and why if i run the same problem with prescribing the velocity vector values in inlet and mass flow in outlet does not lead to divergence.Is there any way to make the code ''accept'' more numerical instabilities so as to accept the mass flow inlet and outlet boundary conditions? Furthermore the combination of prescribing velocity vectors in inlet and mass flow in outlet is correct or wrong even if i can calculate the mass flow in the inlet boundary condition from the velocity vectors? Thanks for your time

 June 5, 2001, 12:28 Re: Numeca Fine #2 John C. Chien Guest   Posts: n/a (1). There are two aspects of your question, namely, (a). Do you know the proper way to formulate your problem, ie, how to define your problem properly (mathematically), (b). Once the problem is defined properly (we don't know what your problem is, yet), do you know how to find a solver algorithm to find the converged solution? (2). These questions are essential. And if the problem (including boundary conditions) is not defined properly, and the solution procedure is not properly selected, then it is difficult to find a converged solution. (3). For the commercial codes, "who knows what is in the black box". For that part, you will have to discuss it with the vendor's support engineers. (4). It is very common to hear that a solution does not converge when using a commercial code. So, when you use a commercial code, follow the sample problems provided. If the sample prblems don't converge, then try something else. (5). You could send your suggestions to the vendor for the code you are using.

 June 6, 2001, 19:54 Re: Numeca Fine #3 clifford bradford Guest   Posts: n/a Specifying inlet and outlet mass flow is probably not well posed. Are you solving an intertnal flow? Fine is a time iterative scheme. the initial condition is specified somewhat arbitrarily. the only way you can specify the inlet and outlet mass flow is if you are certain that at every time step that the mass into any control volume in your domain is exactly equal to the mass flowing out. Of course this is isn't the case because the mass residual in a time iterative solution isn't zero initially (and at no time in the solution even when you get to "machine zero"). at least some portion of your boundary must be "free" to flow as necessary.

 June 16, 2001, 05:05 Re: Numeca Fine #5 clifford bradford Guest   Posts: n/a Dimitris, has your question been sufficiently answered. I'll be happy to discuss it further.

 June 17, 2001, 11:43 Re: Numeca Fine #6 dimitris Guest   Posts: n/a Thx everyone for their help i will try to follow the advices.

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