Francis type hydraulic turbines that have a wide range of operating range for head and flow rates are commonly used in hydropower generation. Every power plant needs its custom designed turbine because the available head and flow rates, which are the main parameters to start the design process, are different for each plant. Guide vanes are the only movable parts of Francis turbines. They control the flow rate through the turbine. In this study, a generalized Computational Fluid Dynamics (CFD) aided design methodology is developed and applied to the design of the turbines of two different power plants. The effects of several parameters, including the shape of the guide vane profile, eccentricity, blade angles, overlapping percentage of the blades, number of guide vanes, and rotor-stator distance are examined. Results are investigated for each parameter in terms of flow physics and important outcomes are determined for turbine designers.