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 February 22, 2010, 08:01 steady or unsteady is better? #1 Member   thanos Join Date: Oct 2009 Posts: 30 Rep Power: 8 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.

 February 22, 2010, 08:39 #2 Senior Member   Bernhard Join Date: Sep 2009 Location: Delft Posts: 790 Rep Power: 13 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.

 February 22, 2010, 17:06 #3 Member   thanos Join Date: Oct 2009 Posts: 30 Rep Power: 8 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.

 February 23, 2010, 02:55 #4 Member   Amol Ramteke Join Date: May 2009 Location: Kolkata Posts: 30 Rep Power: 8 Solve with unsteady first and then move to steady, it will give better convergence.

 February 23, 2010, 12:55 #5 Member   thanos Join Date: Oct 2009 Posts: 30 Rep Power: 8 what time step should i use and how may iterations per time step?

 February 24, 2010, 01:12 #6 Member   Amol Ramteke Join Date: May 2009 Location: Kolkata Posts: 30 Rep Power: 8 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

 February 24, 2010, 06:32 #7 Member   thanos Join Date: Oct 2009 Posts: 30 Rep Power: 8 the smallest mesh size is the distance between the wall and the first cell adjacent to the wall or i understood wrong?

 February 24, 2010, 06:42 #8 Member   Amol Ramteke Join Date: May 2009 Location: Kolkata Posts: 30 Rep Power: 8 Smallest cell inside the domain.

February 24, 2010, 06:51
#9
New Member

Jonathon
Join Date: Feb 2010
Posts: 4
Rep Power: 7
Quote:
 Originally Posted by thanos 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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