Search

In the context of energy shortages and the development of new energy sources, tidal current energy has emerged as a promising alternative. It is typically harnessed by deploying arrays of multiple water turbines offshore. Vertical axis water turbines (VAWTs), as key units in these arrays, have wake effects that influence array spacing and energy efficiency. However, existing studies on wake velocity distribution models for VAWTs are limited in number, accuracy, and consideration of influencing factors. A precise theoretical model (Lam’s formula) for wake lateral velocity can better predict wake decay, aiding in the optimization of tidal current energy array designs. Turbulence in the ocean, serving as a medium for energy exchange between high-energy and low-energy water flows, significantly impacts the wake recovery of water turbines. To simplify the problem, this study uses software ANSYS Fluent 2020 R2 for two-dimensional simulations of VAWT wake decay under different turbulence intensities, confirming the critical role of turbulence intensity in wake velocity decay. Based on the obtained data, a new mathematical approach was employed to incorporate turbulence intensity into Lam’s wake formula for VAWTs, improving its predictive accuracy with a minimum error of 1%, and refining some parameter calculations. The results show that this model effectively reflects the impact of turbulence on VAWT wake recovery and can be used to predict wake decay under various turbulence conditions, providing a theoretical basis for VAWT design, optimization, and array layout.

In this paper, based on the CFD software ANSYS-Fluent, two-dimensional numerical models are established to investigate the hydrodynamic performance of a self-starting H-Darrius vertical axis tidal turbine (VATT) array of three turbines in a triangular layout with 3D in axial and radial distance. Three main aspects are explored in this study: (1) the self-starting performance, power coefficient, flow fields, and blade force of the double-row VATT array, which are compared with a stand-alone turbine, (2) the wake development of the front and rear displacement turbines, and (3) the feasibility of the double-row self-starting VATT array in practical applications. It is found that the power coefficients of the three turbines in the array all improved compared with that of the stand-alone turbine, and as the load increased, the difference between the averaged power coefficient of the array and a stand-alone turbine was more obvious, with a maximum difference of 3%. The main effects of the front turbines on the rear turbine are energy utilization and turbine vibration. Due to the beam effect between the front turbines, the incident flow rate of the rear turbine increased to approximately 1.2 times the free flow rate. However, the greater rotational fluctuations of the rear turbine mean that although it had a higher power factor, it was more susceptible to fatigue damage. The wake of the rear turbine in the array had a much larger area of influence on both the length and width, but the velocity deficit recovered more quickly to over 95% at a distance of 10D behind it. The rate of wake velocity recovery is load-dependent for a stand-alone self-starting turbine, but this was not evident in the arrays. The positive torque of the turbine is mainly generated when the blade rotates through an azimuth angle from 45° to 160° and mainly benefits from the inner side of the blade. For the double-row three-turbine array, the axial and radial spacing of 3D is reasonable in practical applications.