how to predict secondary flow in star-cd. because a famous k-e model fals to predict turbulent flow. example fully developed flow in a square duct. so which model we can use to predict secondary flow in a square duct. please tell me. thanks in advace

Try the quadratic or cubic k-e models, or one of the RSM models.

Cubic k-e is the spawn of satan, go for RSM

... and run it transient.

Don't use cubic...ever