Time Step in LES

salehi144 · August 21, 2010, 07:40

Hi Every one.
i want to solve a turbulent model in fluent with LES. as you know LES is a transient model. my problem is that i dont know how much my time step should be.

is there any body help me?
tnx.

davedong · August 23, 2010, 04:51

hi,
generally speaking, the time step in les is the reciprocal of Re number.
i.e. if the Re number is 2000, the time step should be no more than 0.0005.

salehi144 · August 23, 2010, 05:47

Thank you. dear davedong.
wow what a small time step! my problem Re is 10^5. do you know how much my time step should be? or generelly is there any releation between Re and best time step?

Best Regards.

davedong · August 23, 2010, 22:45

Quote:

Originally Posted by salehi144

Thank you. dear davedong.
wow what a small time step! my problem Re is 10^5. do you know how much my time step should be? or generelly is there any releation between Re and best time step?

Best Regards.

hi,
as i know, it's a rule in Smagorisky model. the reciprocal of Re is equal to the small spacial scale divided by the velocity, in another word, the time step size.
10e-5 time step size is OK. it is absolutely right.
my native language is not english. may it will not make you misunderstand.

August 21, 2010, 07:40	Time Step in LES	#1
salehi144 New Member Saeed Salehi Join Date: Aug 2010 Posts: 27 Rep Power: 15	Hi Every one. i want to solve a turbulent model in fluent with LES. as you know LES is a transient model. my problem is that i dont know how much my time step should be. is there any body help me? tnx.

August 23, 2010, 05:47	Time step is LES for Re=10^5	#3
salehi144 New Member Saeed Salehi Join Date: Aug 2010 Posts: 27 Rep Power: 15	Thank you. dear davedong. wow what a small time step! my problem Re is 10^5. do you know how much my time step should be? or generelly is there any releation between Re and best time step? Best Regards.

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August 23, 2010, 04:51		#2
davedong New Member Dong Liang Join Date: Jan 2010 Location: Shanghai, China Posts: 12 Rep Power: 16	hi, generally speaking, the time step in les is the reciprocal of Re number. i.e. if the Re number is 2000, the time step should be no more than 0.0005.