[orland]

Hi
Could anyone advise me how i can create 2 parallel streams in Fluent without a boundary between them (a shear layer between 2 fluids)?

[duri]

Creating two different fluids is only possible with multiphase, but it has difficulties in capturing shear layer. In worst case try using Eulerian multiphase with two inlets for each phase and patch the initial condition.
Incase of same fluid with different properties let say densities are different. Create two inlet velocities and tune inlet bc value to get the required fluid property (eg, change temperature to adjust density). Patch the domain with the appropriate initial conditions.