Can we get two different flow regimes in a single geometry?
 

My geometry has two inlets and one outlet. I want two different flow regimes at each inlet. From one inlet I want turbulent flow and from other Laminar flow. Is it possible in Star ccm+. If yes, then please tell me how to do it.

There is a transitional model in starccm+. These models use prior knowledge to dampen the turbulence viscosity when the flow is near-laminar or laminar. You should be careful though, and make sure that the model constants you are using is applicable to your case. I don't know which transitional model starccm+ uses, but some are tuned for external flows for example, so you shouldn't apply them to internal flows. You need to refer to the documentation to see which models are being used.

Physically these flows exist but they are difficult to model. Star-CCM does not support both models in the same domain, either only turbulent or only laminar, with exception of transitional turbulence models being used. You can try the transitional models mentioned. It is hit or miss (likely a miss) but it might do better than a non-transitional model.

The problem is not in the inlet and outlet boundary conditions. The issue is which governing equations to use in the domain (i.e. which laminar/turbulence model to use).

The best way to proceed is to choose your favorite turbulence model and apply 0% turbulence at your laminar inlet (that's an ad-hoc definition for laminar flow, flow with no turbulence). So use 0% turbulence intensity at that inlet (length scale is arbitrary if intensity is set to 0). Use the correct turbulence intensity % for the turbulent inlet. You can do this for transitional or non-transitional model.

Just don't do the other way around and use a laminar flow model since that would result in only laminar flow (no turbulence).