Abstract
Inspired by the tubercles on humpback whale flippers, leading-edge tubercles have been incorporated into the design of wings and turbine blades in an attempt to improve their hydrodynamic performance. Although promising improvements, especially in terms of the stall performance, have been demonstrated in the limited research that exists to date, the effectiveness of the leading-edge tubercles seems to be influenced by the base blade. This paper focuses on the introduction of sinusoidal leading-edge tubercles to a base blade developed from the classic NACA0018 airfoil, and numerically investigates the effectiveness of leading-edge tubercles on the hydrodynamics associated with the blade in uniform current with different attack angles. Both the macroscopic parameters, such as the lift and drag forces, and the micro-scale flow characteristics, including the vortex and flow separation, are analyzed. The results indicate that the leading-edge tubercles brings a significant influence on the hydrodynamic forces acting on the blade when subjected to an attack angle greater than 15°. This study also reveals the important role of the turbulence and flow separation on hydrodynamic loading on the blade and the considerable influence of the tubercles on such micro-scale flow characteristics. Although the conditions applied in this work are relatively ideal (e.g., the blade is fixed in a uniform flow and the end effect is ignored), the satisfactory agreement between the numerical and corresponding experimental data implies that the results are acceptable. This work builds a good reference for our future work on the hydrodynamic performance of tidal turbines which adopt this kind of blade for operating in both uniform and shearing currents.
Highlights
Inspired by the tubercles on the humpback whale flippers, leading-edge tubercles have been developed and utilized in airfoils and wings (e.g., [1,2,3,4,5,6,7,8,9]), hydrofoils (e.g., [10]), turbine blades (e.g., [11,12,13,14]) and propellers (e.g., [15]) in order to improve their aerodynamic and hydrodynamic performance, especially in terms of stall performances
The blade undergoes a rotational motion about the axis of the turbine in the real scenario, this paper only focuses on the hydrodynamics associated with a fixed blade with different attack angles to the uniform current flow
3 and the the convergent testtest shown prior, the present numerical approach is applied in order to investigate the effects prior, the present numerical approach is applied in order to investigate the effects of lead- of leading-edge on the hydrodynamic loading on the
Summary
Inspired by the tubercles on the humpback whale flippers, leading-edge tubercles have been developed and utilized in airfoils and wings (e.g., [1,2,3,4,5,6,7,8,9]), hydrofoils (e.g., [10]), turbine blades (e.g., [11,12,13,14]) and propellers (e.g., [15]) in order to improve their aerodynamic and hydrodynamic performance, especially in terms of stall performances. This is evident in the study by Nedic et al [17], in which they investigated the hydrodynamics associated with the NACA0012 air foil with trailing-edge tubercles and concluded that the tubercles weaken the vortex shedding in the wake area of the air foil and, improve the lift-to-drag ratio Such local flow characteristics are at a similar scale to the tubercle size; the arrangement and design of the tubercles, as well as the base foil/bade, are critical in order to secure an expected improvement in hydro- and aerodynamic performance. The blade undergoes a rotational motion about the axis of the turbine in the real scenario, this paper only focuses on the hydrodynamics associated with a fixed blade with different attack angles to the uniform current flow Both the macroscopic parameters (e.g., the lift and drag coefficients), and micro-scale flow characteristics, including the vortex structures and flow separations, are examined to reveal the effect of the tubercles on the hydrodynamic performance of the blade. Water 2021, 13, x FOR PEER REVIEW the tidal turbine adopting the present blades and operating in both uniform and shearing currents, which will be the focus of the stage of our research
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