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Old   May 12, 1999, 11:50
Default steady or unsteady
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thomi
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Hello there,

I am curious about the best way to get a steady state (Q=const) for an incompressible flow field. Is either iterating until convergengence without a time contribution, or a 'pseudo unsteady' state calculation with a time discrtization (implicit or explicit) scheme recommended. I am trying to calculate heat transfer for a steady flow field. Thanks for your trouble

Thomi
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Old   May 12, 1999, 12:13
Default Re: steady or unsteady
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John C. Chien
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(1). The iterative approach and the accelerated transient approach are in a way related. (2). In other words, you can turn the iterative formulation into something like an accelerated transient formulation.( not a true transient) In the iterative solution, you have the old solution and the newly updated solution. These can be viewed as old time solution and the new time solution.
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Old   May 12, 1999, 16:47
Default Re: steady or unsteady
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thomi
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Dear John,

thanks for your reply, but which one is more effective (I mean which method ensures faster convergence? I guess the real steady state i.e without transient term? However, thanks for your reply
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Old   May 12, 1999, 17:16
Default Re: steady or unsteady
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John C. Chien
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(1). In the transient flow approach, you are limited by the existing formula to compute the new solution. So, the option there is limited. (2). On the other hand, there are various methods available to speed up the iterative approach. In other words, you don't have to follow the real physics in the space of iterative approach. (3). So,I think, the use of iterative approach is more efficient for steady state solution. But this is just my feeling, I don't have actual numbers to prove it. This is especially true when our experience with transient flow are related to the use of transient compressible flow formulation, which normally takes a long time to converge. (4). It is maybe a good exercise to solve a problem with two different formulations to check out whether the iterative method is actually faster than the transient method for steady-state solution. It is a very good question. It may not be a bad idea at all to " jump to the conclusion"! instead of slowly reaching the conclusion. The iterative method is basically a guessing game where you can zoom in the final solution. I think this is an area which requires more research.
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Old   May 13, 1999, 05:05
Default Re: steady or unsteady
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thomi
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Dear John,

thanx again for your reply. Yes you are right I will make some benchmark tests to see which of the two is better. But I guess there won't be a universal conclusion, since it might depend on the flow problem to be solved. However, nice hearing from you. Thomi
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