# setting time step size!

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 August 14, 2007, 05:12 setting time step size! #1 raja Guest   Posts: n/a hi all! i am a learner of CFD, could somebody please explain me if there is a standard procedure to follow to set the time step? or is it different for different types of flows such as paraboloc and hyperbolic? thanks in advance....raja

 August 14, 2007, 07:11 Re: setting time step size! #2 test Guest   Posts: n/a Raja, You could get an estimate of time step required for your model using the following simple concept--> Approximately calculate the residence time of the fluid in the domain (eg. if you have inlet velocity of 0.1 m/s and length of domain is 1m, ~residence time = 10 s) usually can be put as (smallest length/velocity scales in the simulation) For cold flow case --> time step could be 1/3 to 1/4 of residence time. Reactive flow --> 1/10 of residence time. time step may need to be less than reaction timescale during start of calculation. The time step could be slowly increased as calculations proceed. Turbo-machinery --> 1/w Buoyancy driven flows --> max time scales which could be used sqrt (L/g B * temp diff) B--> coeff of thermal expansivity L--> length scales associated with vertical temp gradient g--> acceleration due to gravity Use 1/3 to 1/5 of this value calculated Best luck

 August 14, 2007, 08:31 Re: setting time step size! #3 raja Guest   Posts: n/a thank you very much!i got it clear now!

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