Doubts about DES simulation

L3munoz · March 25, 2010, 15:09

Hi everybody!

I'm running a DES simulation but i had some doubts since i'm, let's say, a newbie on it...I know CFL number is very important to fix the time step, however i dont know exactly which cell dimension should i take into account in order to compute it? it seems it has to be in x-direction (this is the moving direction of the flow...) but the point is that the mesh isnt uniform, so should i consider the smallest one?

then i've computed the time step (for instance it's 0.0001 s) how many time steps should i take? i was said to consider the characteristic time of the problem (from a characteristic lenght and a characteristic velocity) but i'm not sure if this is correct. otherwise i'd consider the convergence of Cd (drag coefficient which is usually the common way in my problem) but since it gives instantaneous results...I'm a little lost in this topic and i dont know how long should it run. I run for 150000 iterations but it did just 0.75 s, so i guess this isnt enough...

Please, any advice?? I'd appreciate any help from you cause now i'm blocked...

Regards,

Munoz.

L3munoz · April 1, 2010, 10:50

I post myself to renovate the topic and reactivate the thread...any help please???

March 25, 2010, 15:09	Doubts about DES simulation	#1
L3munoz Member Jorge Muñoz Join Date: Apr 2009 Posts: 56 Rep Power: 17	Hi everybody! I'm running a DES simulation but i had some doubts since i'm, let's say, a newbie on it...I know CFL number is very important to fix the time step, however i dont know exactly which cell dimension should i take into account in order to compute it? it seems it has to be in x-direction (this is the moving direction of the flow...) but the point is that the mesh isnt uniform, so should i consider the smallest one? then i've computed the time step (for instance it's 0.0001 s) how many time steps should i take? i was said to consider the characteristic time of the problem (from a characteristic lenght and a characteristic velocity) but i'm not sure if this is correct. otherwise i'd consider the convergence of Cd (drag coefficient which is usually the common way in my problem) but since it gives instantaneous results...I'm a little lost in this topic and i dont know how long should it run. I run for 150000 iterations but it did just 0.75 s, so i guess this isnt enough... Please, any advice?? I'd appreciate any help from you cause now i'm blocked... Regards, Munoz.

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April 1, 2010, 10:50		#2
L3munoz Member Jorge Muñoz Join Date: Apr 2009 Posts: 56 Rep Power: 17	I post myself to renovate the topic and reactivate the thread...any help please???