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  • FLUENT - Unsteady Flow Past a Cylinder - Step 5

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titleCalculating Time Step Size

The Strouhal number for flow past cylinder is roughly 0.183 as reported by Williamson .
In order to capture the shedding correctly, we should have at least 20 to 25 time steps in one shedding cycle. Let's use 25 for our case.

Latex

\large
$$
{\rm{Sr}} = {fD \over U} = 0.183
$$

For our case, D = 2, U = 1 
 Therefore, shedding frequency f = 0.0915 
 Cycle time,

\large
$$
{\rm{t}} = {1 \over f} = 10.9 sec
$$

 Latex
Therefore, Time Step Size = 10.9/25 = 0.436 sec ~ 0.4 sec
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