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steady or unsteady is better?

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Old   February 22, 2010, 08:01
Default steady or unsteady is better?
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thanos
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Hello to all!

To simulate stall in an airfoil with great accuracy what would give better results? A steady or unsteady solver?

Thanks in advance.
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Old   February 22, 2010, 08:39
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If you perform a steady simulation, you will not be able to find any periodic solutions. If this periodicity occurs in your situation, it may become difficult to get a convergent solution with certain discretization schemes. Transient simulations come with a price of course.
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Old   February 22, 2010, 17:06
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The problem i have with steady solution is that there is no stall, the Cl continues to rise! So, i was wandering if an unsteady solver could correctly calculate it.
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Old   February 23, 2010, 02:55
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Amol Ramteke
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Solve with unsteady first and then move to steady, it will give better convergence.
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Old   February 23, 2010, 12:55
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what time step should i use and how may iterations per time step?
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Old   February 24, 2010, 01:12
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del t = del x/v

del t= time step
del x= smallest mesh size
v= velocity

or just put time step 0.001 and no. of time step (maximum) and 20 iteration per time step
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Old   February 24, 2010, 06:32
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the smallest mesh size is the distance between the wall and the first cell adjacent to the wall or i understood wrong?
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Old   February 24, 2010, 06:42
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Smallest cell inside the domain.
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Old   February 24, 2010, 06:51
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Quote:
Originally Posted by thanos View Post
what time step should i use and how may iterations per time step?
A general rule for time stepping is:

Timestep = (1/10) * ((average cell size) / (average velocity))

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