Simulation of floating offshore vertical-axis wind turbines (FO-VAWT) is challenging due to the high-speed rotation of the blades, movement of the floating platform and complex high Reynolds number turbulent flow with massive separation involved. Addressing such problems requires an efficient numerical approach to robustly handle the dynamics of the geometry while accurately predicting the flow dynamics. The present work presents a framework using moving reference frame formulation (MRF) of Navier-Stokes (NS) equations. The MRF method is based on the absolute velocity formulations in a non-inertial frame, providing further robustness and stability for numerical simulation [1]. The flow equations are discretised using the high-order spectral/hp element method within the Nektar++ framework [2]. By utilising high-order finite element methods, the FSI solver benefits from their low dissipation and dispersion properties. Turbulent flow is modelled using implicit LES method to accurately predict the anisotropic and massively separated flow over the blades. To demonstrate the FSI solver’s capacity for such problems, Reynolds Number, Re, has been set to the order of O(10^4) in order to tailor it to the requirements of the present work. The Reynolds number of this order has applications in small-scale VAWT and in extraterrestrial, low-density atmospheric environments. Platform motion is mimicked by the mass-spring damper model. Application of the FSI solver for FO-VAWT is shown with various flow features examined, extending high-order methods to industrial FSI applications. References [1] Lahooti, Mohsen and others, LES/DNS fluid-structure interaction simulation of non-linear slender structures in Nektar++ framework, Computer Physics Communications, 2023, 282: 108528. [2] Moxey, David and others, Nektar++: Enhancing the capability and application of highfidelity spectral/hp element methods. Computer Physics Communications, 2020, 249(1): 107110