Abstract: Both steady and unsteady Reynolds averaged Navier stokes (URANS) methods were applied to the prediction of turbulent flow inside different subchannels in tight lattice bundle. Two typical configurations of subchannels (i.e., wall subchannel and center subchannel) were chosen to be investigated. The validity of the method was assessed by comparing computational results of axial velocity, wall shear stress and turbulent intensity distributions inside various bundle configurations with the experimental data. The results show that RANS simulations with anisotropic turbulent model produce excellent agreement with experiment, whereas it fails to predict the flow behavior accurately in the case of tightly packed geometries (P/D<1.1). On the other hand, the URANS simulations are in good agreement with the results in tightly packed geometries due to reproducing the flow oscillation in the gap region. Reynolds stress turbulence model (SSG, ORS) are proposed for RANS and SAS turbulence model for URANS simulation.