Fluid-structure interaction of flexible lifting bodies with multi-body dynamics of order-reduced models and the actuator-line method

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The development of complex energy converters presents unresolved demands on simulation tools. This thesis introduces a model-based method for representing fluid-structure interaction, specifically using vertical-axis turbines as a case study. The turbine's kinematics are simulated through a multi-body approach that supports flexible bodies, with dynamics based on order-reduced models. The fluid domain is modeled using Reynolds-averaged Navier-Stokes equations, combined with an actuator-line method that approximates the blade through external forces in the momentum equations. A two-way iterative approach facilitates the coupling of mechanical and fluid solvers, with an improved convergence rate achieved through step prediction based on quasi-Newton methods. Additionally, proper orthogonal decomposition accelerates convergence. An alternative monolithic approach is discussed, highlighting its limitations with the selected solvers. The simulation method is validated against experimental data for vertical-axis turbines in both air and water, demonstrating good agreement with experimental and analytic solutions. The developed tool chain shows enhanced accuracy compared to potential flow and streamtube methods, with significantly lower computational costs than fully meshed solutions. Finally, the simulation of a vertical-axis tidal turbine with flexible blades examines local blade deflections and their relation to wake-body interact