Francis type turbines are commonly used in hydropower generation. Spiral case, stay vanes, guide vanes, runner and draft tube are the main components of the turbine. Available net head and discharge values determine the initial dimensions of these parts according to theoretical and experimental data. In this study, a design methodology is described to optimize the design by integrating in-house Matlab codes and commercial CFD codes. CFD is widely used to solve complex three-dimensional (3D) flows occurring in these types of turbo machines. This paper discusses the basic principles of a computational fluid dynamics (CFD) aided design methodology applied to Francis turbines.