What should be the inlet boundary conditions when using the RANS model for a turbulent jet in CFX 10.0?

The behavior of the jet is very much dependent on the inlet conditions and mesh resolution around the jet's orifice. To prescribe a turbulence intensity on the inflow is just not good enough especially for transient simulations. One needs to simulate an inlet pipe too.

1) The best way is to do a separate simulation of a pipe and get steady-state profiles of velocity, k and epsilon (or omega). Then you use these profiles as BCs for the jet's inlet pipe. Namely, the profiles in the inlet pipe have to be fully developed before coming to the expansion and the jet starts to developed.

2) There is also a simpler way. One can also take empirical correlations for velocity, k and epsilon profiles in the inlet pipe.

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