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How to estimate total time and timestep for unsteady simulations?

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Old   February 22, 2018, 08:42
Default How to estimate total time and timestep for unsteady simulations?
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Hi fellows,

I'm having the hardest time to simulate a turbulent separation bubble induced by a combination of adverse to favourable pressure gradients.

Some of the experimental data known that could help to carry out the unsteady simulation are: two Strouhal number based on bubble length (separation to reattachment point) and reference velocity, Uref = 25 m/s. The first Strouhal number describes the breathing motion of the bubble, St = 0.01 and the second one describes the emission of coherent structures in (by?) the shear layer, St = 0.35.

Could anyone please give me a hint on how to get to see, for example, u' x t??? Of course I need to first find out the appropriate timestep and total time for the unsteady simulation.

Thanks in advance!
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Old   February 22, 2018, 09:05
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I have been using BSL EARSM model on CFX to steady simulation. This was the only model that best showed the flow pattern, compared to experiments (oil-film technique), in the upper wall of the wind tunnel test section in the region of the separated flow.
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Old   February 22, 2018, 17:52
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You should do some careful research on turbulence models to help with this work. Most (if not all) 2 eqn turbuelnce models will be unsuitable for this as they have known deficiencies in getting separation bubbles the correct size. RSM models may help, but you may well have to use an LES style model.

You need to spend a merry day at the library doing a literature review on all this before starting, I would suggest.
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