Despite promising experimental works, high fidelity numerical simulations of chordwise flexible blade are useful to better understanding. However, such simulation remains a challenging problem as it requires a Fluid-Structure Inter- action (FSI) solver capable of accurately predicting the stall dynamics, while computing the deformation of a solid with complex geometry. In this paper, the authors propose a LES-based FSI solver using 3D solid elements for the solid and unstructured grid for fluid and solid solvers. This approach aims at being universal and is based on a partitioned coupling scheme, allowing low density ratios of the structure to the fluid. It uses an original pseudo-solid method for the mesh movement solving, specifically developed for this work. Besides, this solver is suited for massively parallel computing and can perform Dynamic Mesh Adaptation to be able to take into account any solid movement. Both fluid and solid solvers are validated independently before validation of the FSI solver against a 2D laminar benchmark, including mesh convergence study. The entire methodology is then successfully applied to experimental 3D complex case with high Reynolds number, confirming the potential of the FSI solver for its intended use, without geometry restriction. This is finally illustrated with a simulation of an experiment involving a chordwise flexible blade with large deformation, which has never been reproduced with a 3D LES approach in literature so far.