Harmonic loading of horizontal axis tidal turbines due to non-uniform stream profile

Marine hydrokinetic technology offers a possibility to exploit huge untouched water kinetic energy and to meet global efforts in clean and renewable energy production in the near future. Horizontal axis tidal turbines, as part of this technology, operate in harsh environment with severe hydrodynamic loading. Therefore, dynamic loading of bottom fixed horizontal axis tidal turbine, operating in non-uniform stream profile, is considered. Well known blade element momentum theory relationships are transformed using Fourier series analysis and harmonic excitation is determined including hydrodynamic, hydrostatic and centrifugal forces acting on turbine blades. Harmonic loading acting on 2-bladed bottom fixed horizontal axis tidal turbine with output power of 1MW is determined based on the developed theory and the obtained results are compared to those available in the relevant literature. Rather large discrepancies of harmonic forces and moments peak values and amplitudes between obtained and referred, as well as between referred results themselves, are recognized and discussed. Influence of design parameters, i.e. axial velocity profile parameter, hub height and blade number, on harmonic loading functions is investigated and implications of unsteady loading on horizontal axis tidal turbines are pointed out. •Horizontal axis tidal turbines analysis state-of-the art is briefly outlined.•Non-uniform tidal stream velocity profile is considered by BEMT and harmonic analysis using Fourier series.•Obtained results are compared to the available ones, and differences are discussed.•Influence of tidal stream velocity profile parameter, hub height and number of blades on harmonic loading is investigated.