# CFL / Courant Number

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 February 12, 2024, 01:56 CFL / Courant Number #1 New Member   Mathanraj K Join Date: Nov 2023 Posts: 1 Rep Power: 0 Hi ! I have two doubts in using CFL number in transient problems. 1. How to calculate del.x in CFL number in 3D simulation in Fluent? 2. To determine number of time steps based on time step, we need to total time. How to calculate total time? For example, what is the total time of water flow over cylinder when inlet velocity is 50 m/s & cylinder dia is 1 m & cylinder length is 5 m & flow length between inlet & outlet is 21 m? Thank u in advance!

 February 12, 2024, 02:43 #2 Member   Luca Join Date: Mar 2021 Location: Italy Posts: 47 Rep Power: 5 In order to roughly estimate delta X you can take the cubic root of each cell; try to look at the Fluent Theory Guide to see how it evaluates exactly the Courant Number. For the case you have cited, there are graphics that plot the relationship between the Reynolds and Strouhal numbers, you can use them to estimate the frequency, then the shedding time period. Last edited by xisluke; February 13, 2024 at 03:06.

 Tags cfl, courant, fluent, mesh size, transient 3d