How to conduct transient LES simulation
 

Hi,

I want to simulation the process of a jet using LES. The duration of the jet is about 0.5s . I know how to simulaiton a constant jet with LES. But when I try to simulate the unsteady jet, the results showed that the jet traveled along a line other than dispersion. I do not know what is the proble.
I know in the steady LES simulation, a long time period is required to get statistic results. However, in transient LES simulation, due to the short term of the jet, the LES can not be stable. So, would anyone help me to figure it out? What is the process of the transient simulaiton using LES in FLUENT. Thanks!