Multi-Objective Hydrodynamic and Structural Design Optimization of Tidal Stream Turbine Airfoil Sections Using NSGA-II and RANS CFD Validation

Tidal stream turbines operate under highly demanding marine environments, where blades are subjected to extreme hydrodynamic loads, fatigue, and cavitation risks. As a result, designing hydrofoil profiles that simultaneously maximize aerodynamic/hydrodynamic efficiency (C_L/C_D) and maintain structural integrity is critical. This study presents an automated, multi-objective design optimization framework for two-dimensional hydrofoil sections of horizontal axis tidal stream turbines. The profiles are parameterized using Class Shape Transformation (CST) and evaluated using a coupled aerodynamic-structural model. Hydrodynamic coefficients are computed via XFOIL, and structural bending stresses are modeled using a double-clamped Euler-Bernoulli beam representation under distributed hydrodynamic pressure loading. We applied NSGA-II multi-objective genetic search to navigate the inherent trade-off between maximizing lift-to-drag efficiency and minimizing the root bending stress coefficient. Two optimal designs—the Best-Efficiency hydrofoil (Opt. Best-η) and the Knee-Point compromise hydrofoil (Opt. Knee)—were selected from the Pareto front. To validate the optimization results, two-dimensional steady-state Reynolds Averaged Navier-Stokes (RANS) simulations with the k-ω Shear Stress Transport (SST) turbulence model were conducted in OpenFOAM 2412. The CFD results confirm that the Optimized Knee profile achieves a lift-to-drag ratio (L/D) of 19.58 at the design angle of attack (α = 0°), representing a 30.3% improvement over the baseline NACA 63-815 profile (L/D = 15.03), while maintaining a favorable stress profile. This study demonstrates the utility of coupling fast-evaluation panel methods with structural models for rapid multi-objective screening, followed by high-fidelity RANS validation for marine hydrofoil development.