Integrated evaluation of geometric and operating parameters on H-Darrieus hydrokinetic turbine performance and structural response

Hydrokinetic turbines (HKTs) are promising devices for extracting energy from marine and riverine currents and open channels. This study presents an integrated numerical and analytical investigation of H-Darrieus HKTs. Two-dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations, validated against experimental power data, were used to evaluate the coupled effects of rotor solidity ( σ ) and blade number ( N ) on performance and instantaneous sectional loads across a range of tip-speed ratios ( TSRs ). Twelve rotor configurations were assessed using the normal, tangential, thrust, and lateral forces. These loads were subsequently processed by the same closed-form Euler-Bernoulli beam, equivalent-homogeneous CFRP, fatigue-indicator, and frequency-ratio formulations. For every configuration, the maximum absolute sectional load recorded over a complete revolution was applied uniformly along the modeled span, defining a common severe global-bending envelope. The results were consistent with the dynamic similarity between wind and hydrokinetic Darrieus rotors within the investigated range, supporting the use of an empirical solidity-based correlation for estimating the optimal TSR ( TSR opt ) within the evaluated cases. Furthermore, within the investigated NACA 0021 geometry, turbine scale, inflow velocity, turbulence condition, and TSR range, σ = 0.204 combined with N = 4 or 5 provided the most favorable balance between hydrodynamic performance and the adopted comparative structural indicators. In overall conclusion, rotors with higher solidity and an intermediate number of blades are favored, whereas low-solidity rotors with a high number of blades showed unfavorable structural trends and higher relative risk.