3D Simulation with Flow-Induced Rotation for Non-Deformable Tidal Turbines

The overall potential for recoverable tidal energy depends partly on the tidal turbine technologies used. One of problematic points is the minimum flow velocity required to set the rotor into motion. The novelty of the paper is the setup of an innovative method to model the fluid–structure interactions on tidal turbines. The first part of this work aimed at validating the numerical model for classical cases of rotation (forced rotation), in particular, with the help of a mesh convergence study. Once the model was independent from the mesh, the numerical results were tested against experimental data for both vertical and horizontal tidal turbines. The results show that a good correspondence for power and drag coefficients was observed. In the wake, the vortexes were well captured. Then, the fluid drive code was implemented. The results correspond to the expected physical behavior. Both turbines rotated in the correct direction with a coherent acceleration. This study shows the fundamental operating differences between a horizontal and a vertical axis tidal turbine. The lack of experiments with the free rotation speed of the tidal turbines is a limitation, and a digital brake could be implemented to overcome this difficulty.

Numerical Model of a Vertical-Axis Cross-Flow Tidal Turbine

An array of close-packed contra-rotating cross-flow vertical-axis tidal rotors, a concept developed to maximize the fraction of flow passage swept, has potential advantages for hydrokinetic power generation. To predict the commercial feasibility of such rotors in large-scale application, a numerical model of a vertical-axis turbine (VAT) with a torque-controlled system is developed using an actuator line model (ALM). The open-source OpenFOAM computational fluid dynamics (CFD) code is first coupled with this ALM model, and efficiently parallelized to examine the characteristics of turbulent flow behind a vertical axis tidal turbine. The numerical model is validated against previous experimental measurements from a 1:6 scale physical model of a three-bladed reference vertical axis tidal turbine at the University of New Hampshire (UNH-RM2). Satisfactory overall agreement is obtained between numerical predictions and measured data on performance and near-wake characteristics, validating the numerical model. Details of the model setup and discussions on its output/results are included in the paper.

Study on Hydrodynamic Configuration Parameters of Vertical-Axis Tidal Turbine

In this paper, a numerical code for predicting the hydrodynamic performance of vertical-axis tidal turbine array is developed. The effect of the tip speed ratio, solidity, and preset angle on the hydrodynamic performance are discussed using a series of calculations. The load principle of the rotor and the variation principle of the turbine power coefficient are studied. All these results can be considered as a reference for the design of vertical-axis tidal turbines.

Wake of a Ducted Vertical Axis Tidal Turbine in Turbulent Flows, LBM Actuator-Line Approach

Vertical axis tidal turbines are devices that extract the kinetic energy from tidal currents. Tidal currents can be highly turbulent. Since ambient turbulence affects the turbine hydrodynamic, it is critical to understand its influence in order to optimize tidal farms. Actuator Line Model (ALM) combined with Large Eddy Simulation (LES) is a promising way to comprehend this phenomenon. In this article, an ALM was implemented into a Lattice Boltzmann Method (LBM) LES solver. This implementation gives good results for predicting the wake of a vertical axis tidal turbine placed into a turbulent boundary layer. The validated numerical configuration was then used to compute the wake of a real size ducted vertical axis tidal turbine. Several upstream turbulence rates were simulated. It was found that the shape of the wake is strongly influenced by the ambient turbulence. The cost-to-precision ratio of ALM-LBM-LES compared to fully resolved LBM-LES makes it a promising way of modeling tidal farms.

Numerical simulations of biofouling effects on the tidal turbine hydrodynamic

Biofouling by benthic organisms must be considered for tidal turbine operation and maintenance because it modifies hydrodynamics (drag and resistance) and could be detrimental to the turbine performance. We investigate vortices modification downstream a tidal turbine due to biofouling using numerical modeling. Firstly, 2D flow downstream a clean Darrieus vertical axis tidal turbine is simulated using a dynamic mesh for different tip speed ratio. Results agree the former studies. Simulations are very sensitive to turbulence modeling. To ensure an acceptable computing time, only LES and RANS are used. Secondly, an airfoil with barnacles is modeled in two dimensions for various fouling height and spacing with different flow incidences. Barnacle height has more influence on flow than the barnacle density. Then barnacles and mussels with various characteristics are fixed on blades. Vorticity fields are strongly changed by organism shapes. Mussels size has little impact on vorticity patterns. A few mussels could have stronger impact than a fully colonization. A 3D simulation is performed with a shape of barnacles from new in-situ measurements. Finally a colonized tidal turbine is simulated is modelled.

An Unsteady Boundary Element Model for Hydrodynamic Performance of a Multi-Blade Vertical-Axis Tidal Turbine

An unsteady boundary element model is developed to simulate the unsteady flow induced by the motion of a multi-blade vertical axis turbine. The distribution of the sources, bound vortices and wake vortices of the blades are given in detail. In addition, to make the numerical solution more robust, the Kutta condition is also introduced. The developed model is used to predict the hydrodynamic performance of a vertical axis tidal turbine and is validated by comparison with experimental data and other numerical solutions available in the literature. Good agreement is achieved and the calculation of the proposed model is simpler and more efficient than prior numerical solutions. The proposed model shows its capability for future profile design and optimization of vertical axis tidal turbines.

Study of Hydrodynamic Interference of Vertical-Axis Tidal Turbine Array

The hydrodynamic interference between tidal turbines must be considered when predicting their overall hydrodynamic performance and optimizing the layout of the turbine array. These factors are of great significance to the development and application of tidal energy. In this paper, the phenomenon of hydrodynamic interference of the tidal turbine array is studied by the hydrodynamic performance forecast program based on an unsteady boundary element model for the vertical-axis turbine array. By changing the relative positions of two turbines in the double turbine array to simulate the arrangement of different turbines, the hydrodynamic interference law between the turbines in the array and the influence of relative positions on the hydrodynamic characteristics in the turbine array are explored. The manner in which the turbines impact each other, the degree of influence, and rules for turbine array arrangement for maximum efficiency of the array will be discussed. The results of this study will provide technical insights to relevant researchers.