Generation and distribution of turbulence-induced loads fluctuation of the horizontal axis tidal turbine blades

Abstract

Horizontal axis tidal turbines (HATTs) working in a complex flow environment will encounter unsteady streamwise flow conditions that affect their power generation and structural loads, where power fluctuations determine the quality of electricity generation, directly affecting the grid and reliability of the power transmission system; fatigue loads affect various structures and mechanical components of the turbine, directly determining the lifespan and reliability of the turbine. To gain insight into the generation mechanism and distribution of these excitations, a large eddy simulation is employed to analyze the inflow turbulence and unsteady forces excitations by a three-blade HATT. A spectral synthesizer was used to generate incoming turbulence flow. The strip method was applied on the HATT by dividing the blade into 20 strips. The thrust received by each strip and the flow velocity upstream and downstream of the blade's root, middle, and tip were monitored. The distribution of unsteady loads on the blades was analyzed, as well as the relationship between flow velocity upstream and downstream of the blade and the unsteady characteristics of the blades. The simulation results show that the unsteady hydrodynamic fluctuations of the HATT blades reach up to 57.44% under a turbulent intensity of 10%. Through intuitive analysis of flow separation on the suction surface of the blade at various moments under a low tip speed ratio, we can comprehend the variations in inflow velocity and flow separation on the blade surface. Analyzing the distribution of blade load from root to tip reveals that the maximum load values are concentrated in the 14th–16th strips, corresponding to the region from 0.7R to 0.8R. Moreover, the middle and tip sections of the blades predominantly contribute to the harmonics of the 3BPF (blade passing frequency) and broadband, with the middle section making a greater contribution. The tip section primarily contributes to harmonics above 3BPF. This research want to makes a valuable contribution to the comprehensive understanding of turbulence-induced exciting forces and the practical engineering design of HATT.