[rohani]

I am planning to simulate a supersonic nozzle with DES turbulence model using ANSYS FLUENT 17.1 . I read in a FLUENT guidebook that it is necessary to use adaptive time step with DES model.

How do I choose the time step in DES model, Do I need to use fixed or adaptive time step?
It should be noted when using DES model in FLUENT, You will receive a warning message: turbulence model should only be used with the Bounded Second Order Implicit Transient Formulation. It's confusing because adaptive time step isn't selectable along with the Second Order Transient Formulation.