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July 12, 2016, 00:46 |
How to determine time steps?
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#1 |
New Member
Join Date: Jul 2016
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my fyp topic is "investigating drag by modifying surface pattern". i need to study the lift of a sepak takraw ball under unsteady state. how can i determine the time steps and also the maximum inner itertaion? I know it deals with courant number. but i dont know how to determine the courant number.
I am working on star ccm+. |
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July 13, 2016, 15:49 |
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#2 |
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Matt
Join Date: Aug 2014
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you will want to chose a time step based on a target value of your courant number. this value depends on your solver. If it is an explicit solver you need to keep courant less than or equal to 1 for stability. For implicit solver you can go much higher, in some cases up to 100.
once you establish a target for courant number then you look at your mesh and find the areas with high velocity and small cell size (where max CFL will likely lie). Then use the definition of courant number to calculate the time step size that satisfies your courant number target, local cells size and flow velocity... |
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July 13, 2016, 23:23 |
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#3 | |
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Quote:
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July 16, 2016, 19:55 |
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#4 |
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CFD
Join Date: Nov 2010
Location: United States
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You need to use the following relation according to wikipedia
https://en.wikipedia.org/wiki/Couran...Lewy_condition CFL = (u*delta_t)/delta_x where, delta_t = is the step size you aim to calculate delat_x = the dimension size where the maximum velocity occurs. u = is the free stream velocity in your case is 6m/s. CFL = Cournat number. Best, |
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