This work is devoted to a computational investigation of the cavitation and mixing characteristics of two miscible (Schmidt number Sc = 10(3)) turbulent water flows with different viscosity ratios in a Venturi tube. The 2D axis-symmetric RANS and 3D LES turbulence models are used for the prediction of flow characteristics. The numerical results reveal that the RANS solutions underpredict the rate of vapour production and overestimate the mixing rate of two miscible fluids in comparison to LES simulations for the inlet Reynolds number of 19 738 (Case-1) and 19 286 (Case-2). In particular, there is a larger cavitation zone in the Venturi tube with LES in comparison to RANS calculations.