Offshore wind turbines are becoming increasingly popular due to their higher wind energy harnessing capabilities and lower visual pollution. Researchers around the globe have been reporting significant scientific advancements in offshore wind turbines technology, addressing key issues, such as aerodynamic characteristics of turbine blades, dynamic response of the turbine, structural integrity of the turbine foundation, design of the mooring cables, ground scouring and cost modelling for commercial viability. These investigations range from component-level design and analysis to system-level response and optimization using a multitude of analytical, empirical and numerical techniques. With such wide-ranging studies available in the public domain, there is a need to carry out an extensive yet critical literature review on the recent advancements in offshore wind turbine technology. Offshore wind turbine blades’ aerodynamics and the structural integrity of offshore wind turbines are of particular importance, which can lead towards system’s optimal design and operation, leading to reduced maintenance costs. Thus, in this study, our focus is to highlight key knowledge gaps in the scientific investigations on offshore wind turbines’ aerodynamic and structural response. It is envisaged that this study will pave the way for future concentrated efforts in better understanding the complex behavior of these machines.

Understanding the connection between physiology and kinematics of natural swimmers is of great importance to design efficient bio-inspired underwater vehicles. This study looks at high-fidelity three-dimensional numerical simulations for flows over an undulating American eel with prescribed anguilliform kinematics. Particularly, our work focuses on why natural anguilliform swimmers employ wavelengths shorter than their bodylengths while performing wavy kinematics. For this purpose, we vary the undulatory wavelength for a range of values generally observed in different aquatic animals at Strouhal numbers 0.30 and 0.40. We observe that our anguilliform swimmer is able to demonstrate more suitable hydrodynamic performance for wavelengths of 0.65 and 0.80. For longer wavelengths, the swimmer experiences large frictional drag, which deteriorates its performance. The wake topology was dominated by hairpin-like structures, which are closely linked with the underlying physics of anguilliform swimming found in nature.

The wavelength of undulatory kinematics of fish is an important parameter to determine their hydrodynamic performance. This study focuses on numerical examination of this feature by reconstructing the real physiological model and kinematics of steadily swimming Jack Fish. We perform three-dimensional numerical simulations for flows over these models composed of the trunk, and dorsal, anal, and caudal fins. Moreover, we prescribe the carangiform-like motion for its undulation for a range of wavelengths. Undulation with larger wavelengths improves the hydrodynamic performance of the carangiform swimmer in terms of better thrust production by the caudal fin, lower drag production on the trunk, and reduced power consumption by the trunk. This coincides with the formation of stronger posterior body vortices and leading-edge vortices with more circulation on the caudal fin. The real kinematics of Jack Fish surpasses the performance of those with prescribed motion owing to the flexibility of the caudal fin.

The effects of trailing edge shape on the vortex dynamics and surface pressure distributions on pitching foils are examined using direct numerical simulation. Results are presented for a Reynolds number of $1\times {10}^4$ and a Strouhal number of 0.5, which corresponds to the Strouhal number for maximum efficiency as found by experiment [Van Buren et al., Phys. Rev. Fluids 2, 014702 (2017)]. For the trailing edge shapes studied here (square, convex, and concave), the maximum instantaneous thrust occurs at the moment when the vortex detaches from the trailing edge. At the same time, the surface pressure gradients across the panel surfaces increase, while viscous forces drop. The leading edge vortices are seen to merge with the side edge shear layers, and as they wrap around the trailing edge the thrust generation is depressed just prior to the instance of maximum thrust. This process, combined with momentum transfer associated with switching the direction of pitching, produces irregular variations in the thrust and side forces. Compared to the square panel, the wake of a concave trailing edge panel exhibits strong three-dimensional effects on its side edges leading to slower wake contraction, smoother vortex bending, and lower thrust. In contrast, the convex trailing edge panel allows detaching structures to grow longer prior to their detachment, resulting in bent structures formed closer to the trailing edge, which leads to faster wake contraction and higher thrust. Skeleton models of the wakes help explain their underlying structure.