to overcome recirculation we extend the outlet. what is the maximum distance that we can extend. suppose my domain length is say 1m if i have recirculation near the outlet how much i can extend the outlet. is there any thumb rule for that.

I read from one book, for flow in a tube, it would be 10 times of the diameter at least. Anyway, in my humble opinion, you extend it at some length, then see in Post if the recirculation zone is in the domain. If it is not, extend it more.

Hope that help.

Hi,

The length of recirculation is problem dependant. For low Re flows 10x diameter might be OK but for high Re flows you might need 100x diameter.

As Atit says, have a guess, do a simulation and check it and if too short extend it.

Glenn Horrocks

Or insert a porous domain that evens out the flow at the outlet. Don't spend to many cells on doing otherwise -Dr. Flow Squad http://tinyurl.com/2gkjh8