Geometrical effects of bio-inspired humpback whale flipper tubercles on hydro turbine blade performance
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Date
2019
Authors
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Publisher
Universiti Teknologi Malaysia
Abstract
Hydrokinetic is arguably the best energy generator and most preferred for harvesting energy compared to fossil fuel and wind energy. The preference is due to source depletion and unpredictable nature. This research aims to study the effect of blade geometry on the hydrodynamic and structural performances of hydro turbine blade. The geometry of the blade is inspired by humpback whale flippers tubercles. This study filled the literature gaps by examining the rarely explored maximum attack angle of flow and the corresponding structural responses of the bio-inspired blade for various tubercles geometries. Then, a numerical analysis was conducted to formulate relationship for practical design purpose. The analyses in this study were performed using ANSYS 14.0, which were validated with scaled-down experimental model data and analytical solutions on fluid flow and structural behaviours. Only 1-way interaction between the fluid and blade structure was considered in the numerical analysis, where the pressure load was imported from the fluid flow analysis. A flat blade and bio-inspired blades with tubercle wavelengths, λ = 50 mm, 100 mm, 150 mm, and amplitudes, A = 5 mm, 10 mm, 15 mm, were studied in steady state flow velocity of 0.418 m/s. To link to practical application, flow and structural responses of 3-blade turbine system in a real river environment were further modelled to demonstrate more realistic fluid on the structural behaviour. Studies on the streamlines, pressure distribution, and vortices around the blades, as well as stresses and displacement of blades were carried out. Blade with the shortest λ and middling A revealed the best hydrodynamic performance, where 33.8% longer reattachment length of flow as compared to the flat blade was observed and resulted in a larger low-pressure area in the wake. This offers the potential of generating higher experienced acceleration for better blade rotation for hydro-power generation. The beneficial hydrodynamic effects in terms of velocity and pressure were found in good agreement with the newly introduced vortical parameters, including area, perimeter, and Feret diameters. On the other hand, the structural responses of the blades due to fluid load were within the allowable safety limits for stress and displacement. In general, blades with the longest λ exhibited the lowest von Mises stress while those with the shortest λ and A experienced the least displacement. Overall, 50λ10A blade is the best optimised tubercle geometry, considering both hydrodynamic and structural behaviours. A set of practically-convenient equations formulated from the stress and displacement along the tubercles peak and trough of blades were established for various λ and A, in which the equations are important for practical convenience. Higher stress at tubercles peaks and around the supported end of blade demonstrated the blade most likely failure area in bending stress. All aforementioned findings contribute significant knowledge on benefits of tubercles on turbine blade for improved hydro-structural performance, providing engineers the reference and preliminary in designing the hydro turbine.
Description
Thesis (PhD. (Civil Engineering))
Keywords
Hydrodynamics—Experiments, Geometric analysis, Turbines—Blades