am trying to run unsteady case, and in order to do that I need to estimate (delta t)

delta t= Typical cell size/characteristic flow velocity

(this eqution from fluent.com)

can any body help in this

thanks

In 3d you could use cube root of volume/#_of_cells. Just an estimate.

HTH

Hi!

i would use the finest grid cell for calculation. So you can be sure that flow is resolved everywhere

Best whises Ralf

[oozcan]

which one is preferred to be used? both approximations are applicable.

[Antanas]

Originally Posted by oozcan

which one is preferred to be used? both approximations are applicable.

In usual cases it is recommended dt = L / 3V. L - characteristic length, V - characteristic velocity. L = cell characteristic size may be very restrictive, but also safe in terms of convergence.

If your mesh is relatively uniform, then you may estimate cell size as cubic root of Domain Volume / Number of Cells. Anyway it is safe to use minimum cell size.