Free surface flows are extremely complex and appear in various cases such as chemistry, oceanography, thermodynamics and turbomachinery. Their complexity is due to the fact that they are composed of two distinct phases which are only separated by a thin interface through which energy and heat transfers can occur. There are different types of free surface flows, such as liquid-liquid, illustrated by the injection of an oil droplet in water, and liquid-gas, for example bubbles in boiling water. We have focused our study on free surface flows in the field of hydraulic turbomachinery, and more precisely in Pelton turbine buckets. The theoretical and experimental studies conducted up to now have considerably enlightened the physics linked to these applications. However, there are still many mysteries left to be explored and the time spent during the design phase could certainly be reduced. Unfortunately, the codes needed to numerically model these flows have only recently appeared on the market and their reliability is therefore constantly questioned. In this study, we propose the development of a free surface flow analysis method based on a test case which approaches the Pelton bucket : the deviation of a water jet by a plane plate. This case allowed us to understand the physics of the flow, especially by comparing numerical and experimental results. Finally, based on the previous study, the flows within non-rotating and rotating 3D buckets were simulated. In parallel, transient measurements of the flows brought new insight on the detailed behavior of the water in the buckets. These numerical and experimental results were then compared in order to offer a complete validation of the proposed method.