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Timescale convergence?!

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Old   April 15, 2016, 08:45
Default Timescale convergence?!
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Tim
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Hi guys,

I'm running a NACA0015 profile at low reynolds numbers (10000-1000000) with steady sst including gamma-theta transition model. I varied my timescale to become a converged (steady state) solution. But I found out, that in some cases both decreasing and increasing the timescale from my converged timestep gives me an oscillating (transient) result.

My question is, does the "good" timescale maybe damp transient effects so the solution can convergate?

Cheers
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Old   April 15, 2016, 14:57
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at what AOA?
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Old   April 16, 2016, 05:44
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AoA=0, critical Re from 10000 til 100000. above 100000 it's ok.
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Old   April 16, 2016, 07:42
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If the flow is not in the gross separated flow regime (which I suppose it is not at AOA=0), then this is probably a laminar separation bubble. They tend to be unstable and jiggle about quite a bit. If the bubble is small it probably does not affect things much but at low-moderate Re (50k-200k for many airfoils) the separation bubble can be large. It might be important in this Re range.
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