Experimental and numerical study of a dual configuration for a flapping tidal current generator

Abstract

In this study, we conduct experimental and consecutive numerical analyses of a flapping tidal current generator with a mirror-type dual configuration with front-swing and rear-swing flappers. An experimental analysis of a small-scale prototype is conducted in a towing tank, and a numerical analysis is conducted by means of two-dimensional computational fluid dynamics simulations with an in-house code. An experimental study with a controller to determine the target arm angle shows that the resultant arm angle is dependent on the input arm angle, the frequency, and the applied load, while a high pitch is obtained simply with a high input arm angle. Through a parametric analysis conducted while varying these factors, a high applied load and a high input arm angle were found to be advantageous. Moreover, the optimal reduced frequency was found to be 0.125 in terms of the power extraction. In consecutive numerical investigations with the kinematics selected from the experiments, it was found that a rear-swing flapper contributes to the total amount of power more than a front-swing flapper with a distance of two times the chord length and with a 90° phase difference between the two. The high contribution stems from the high power generated by the rear-swing flapper, which mimics the tail fin movement of a dolphin along a flow, compared to a plunge system or a front-swing system, which mimics the tail fin movement of a dolphin against a flow. It is also due to the fact that the shed vorticities of the front-swing flapper slightly affect negatively or even positively the power performance of the rear-swing system at a given distance and phase angle.

Surrogate modeling of fluid dynamics with a multigrid inspired neural network architecture

“…In the following sub-sections, three sets of fluid dynamics simulations are described. These cases are typical fluid dynamics problems commonly studied in literature, and are used here as a basis for comparing the performance of the U-Net model and the proposed U-Net-MG model (Jihoon Kim et al, 2015;Mahir & Rockwell, 1996;Ooi et al, 2020;Read et al, 2003). All simulations are run via the opensource OpenFOAM platform with the k-ω SST turbulence model.…”

“…In the following sections, we present our results on the following fluid dynamical systems: 1) flow past a stationary cylinder, and flow due to two cylinders in out-of-phase motion; and 2) flow past an oscillating foil. These examples are chosen as the former set of scenarios are commonly studied canonical problems in fluid dynamics, with relevance to the marine industry such as in understanding the interaction between risers (Hu & Zhou, 2008;Huera-Huarte & Jiménez-González, 2019;Liu & Jaiman, 2016;Wang, Xiao, Zhu, & Incecik, 2017), while the latter set of scenarios are greatly relevant to the areas of propulsion or energy harvesting (Andersen, Bohr, Schnipper, & Walther, 2017;Jihoon Kim et al, 2015;Kinsey & Dumas, 2008;Read, Hover, & Triantafyllou, 2003). Critically, they also encompass an interesting range of problems in surrogate modeling, including flow in a scenario with a fixed object and constant boundary conditions (flow past a stationary cylinder), flow in a scenario with varying inlet boundary conditions and moving objects (flow past two cylinders in out-of-phase motion), and flow in a scenario with consistent inlet boundary conditions and moving objects but with varying geometries (flow past oscillating foils of different geometries).…”

Effect of wake interaction on the response of two tandem oscillating hydrofoils

“…They found that it is possible to improve performance of an oscillating foil system through multi-stage foils arranged in tandem form. Kim et al 29 carried out experimental and consecutive numerical analyses of an oscillating tidal current generator with front-swing and rear-swing flappers. They concluded that the oscillating foil micro-hydropower generator has significant further development potential.…”

“…28 The experiments confirmed the competitive performance of the oscillating foil hydrokinetic turbine compared to rotor-blade designs. Kim et al 29 carried out experimental and consecutive numerical analyses of an oscillating tidal current generator with front-swing and rear-swing flappers.…”

Numerical Study on the Effect of Non-Sinusoidal Motion on the Energy Extraction Performance of Parallel Foils

“…They observed that the semi-empirical model of the dynamic stall is effective in predicting the aerodynamic force and efficiency. The numerical research on the extraction performance of foil discusses the potential effect factors like the oscillation motion, the motion parameter, the Re number and the profile of foil by the control variable method and the traditional optimization algorithm, aiming at finding a higher power output and extraction efficiency [6][7][8][9][10][11][12][13]. The oscillation process always adopts the sinusoidal motion, however, some researchers tried to use non-sinusoidal motion on foil for further investigations.…”