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Old   March 20, 2012, 07:12
Default Basics of Timescale
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Neal
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Dear All,

Please can anyone tell me why we use Timescale/ Timestep in CFD simulations?

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Old   March 20, 2012, 09:50
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? what do you mean?
Are you asking why there is temporal discretization in CFD?
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Old   March 20, 2012, 12:10
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For example in CFX we use Physical / Automatic Timescale or in FLuent we used Timestep.

I just want to know that what is the purpose of using timescale.
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Old   March 22, 2012, 08:03
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Firstly, a timescale is used in CFX as it is a fully implicit solver AND in Fluent (for the explicit solver) it uses relaxation factors.
The idea is to under relax your discretized equations as your solution proceeds to a steady state converged state. By under-relaxing your variables you are allowing only a part of the old value to be used to calculate the new value and so on so that your solution doesn't go out of hand and diverge.
I hope this makes sense to you.

In CFX the timescale refers to this under relaxation and is in no way related to the transient timestep.

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Luke
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Old   March 22, 2012, 08:05
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Luke,

Thanks a lot.
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