Today, the study and research on flexible rotor blades dominate modern aerodynamic systems, especially in the fields of wind energy and aviation. The performance of flexible blade rotors is one of the key research objectives, as it is influenced by various factors such as aerodynamic design, flexibility, number of blades, etc. In this context, this study investigates a numerical exploration of fluid structure interaction aimed at studying the elastic behavior of flexible bladed rotors. This study uses a robust bidirectional fluid-structure interaction (FSI) approach developed under ANSYS Workbench software. This approach couples the transient structure solver to the fluid dynamics solver while respecting the coupling conditions at the interfaces. The rotors studied consist of moderately flexible blades with a simplified rectangular geometry. The main objective of this work is to analyze the effect of flow and blade number on the stress distribution in the blades. To this end, three rotor configurations are used. These rotors are submerged in water in order to apply more load. The results demonstrate that the behavior of the different rotors is similar, and the stress is highly dependent on the aerodynamic loads and on the generated deformations.In fact, as the aerodynamic loads applied to the rotors increase, the blades tend to reconfigure and deform significantly in order to maintain moderate structural stresses, thus ensuring their resistance to critical aerodynamic loads.