Single Vertical Axis Wind Turbine Research Articles

Aerodynamic efficiency assessment of a cross-axis wind turbine integrated with an offshore deflector

The present work examines the performance of an offshore cross-axis wind turbine (CAWT) with a flow deflector by integrating numerical and analytical methods. The deflector's geometry redirects flow in all directions, causing it to exit vertically and collide with the wind turbine's horizontal blades. In contrast, the blades of a vertical axis wind turbine (VAWT) harness the power of horizontal wind flow. The total power absorbed by the horizontal and vertical turbine blades represents the power of CAWT. In this study, the speed of the outflow from the deflector was initially determined through numerical simulation. The numerical simulation output was then utilized as an input for analytical Double Multiple Stream Tube (DMST) and Blade Element Momentum (BEM) methods to evaluate the vertical and horizontal turbine blades, respectively. This approach reduces the overall simulation time and establishes an offline coupling between analytical and numerical approaches. The findings of this research have unveiled a promising future for offshore wind energy generation. Through the implementation of a modeled deflector on a Cross-Axis Wind Turbine (CAWT), the power output reached a remarkable 19 KW with a power coefficient of 0.35 at an 8.4 m/s wind speed. The results indicate that the CAWT with the deflector produced a power output 35 % higher and was 45 % more efficient than a single Vertical-Axis Wind Turbine (VAWT). These outcomes illustrate the potential for greater energy production and efficiency in offshore wind farms.

Enhancing Wind Farm Efficiency Through Active Control of the Atmospheric Boundary Layer’s Vertical Entrainment of Momentum

In contemporary wind farm design, the primary focus has traditionally been on reducing wake interference to optimize energy capture from horizontal wind flows. However, with the scaling up of wind farms, their interaction with the Atmospheric Boundary Layer (ABL) evolves, making vertical entrainment the main mechanism for the exchange of momentum and energy. This study introduces a methodical approach to augment the efficiency of large-scale offshore wind farms by actively controlling this vertical entrainment of momentum within the ABL. The strategy involves the precise engineering of advection fluxes to alter wind flow dynamics, utilizing turbines as effective vortex generators, toward a process of ”regenerative wind farming.” This setup aims to create a vorticity and vertical flux system akin to those observed in highly unstable ABLs. Expanding upon previous studies that focused on single Vertical Axis Wind Turbines (VAWTs), our research explores the implementation of multi-rotor systems equipped with lift-generating wings. These systems are designed to exert forces perpendicular to the prevailing wind direction, thus creating trailing vortices and directing the flow orthogonally for improved vertical advection. This research is part of a comprehensive investigative framework that combines experiments and multifidelity simulations. The current study extends those findings to wind farm simulations, aiming to assess the impact of ABL control on a full wind farm scale. The first part of the work validates an established analytical wind farm performance model against real wind farm data for thirty-one wind farms in the North Sea and Baltic Sea. The results confirm the predicted trend of decreased performance with increased wind farm size and density. The model is used to calculate the performance of a wind farm for varying regimes of vertical entrainment due to the creation of large-scale circulatory systems. The results are compared against 3D vortex simulations of the full wind farm in ”regenerative wind farming” mode. Our results demonstrate a notable improvement in wind speeds at the turbine hub height and the potential to double the feasible density of wind farms without compromising efficiency compared to traditional setups. These findings suggest a promising pathway towards a more sustainable and profitable future in wind energy, achieved through the strategic manipulation of ABL momentum, regenerating the energy in the wind farm.

Numerical method for steady ideal 2‐D flows of finite vorticity with applications to vertical‐axis wind turbine aerodynamics

AbstractThis paper presents a new method for approximately modeling 2‐D ideal steady fluid flows with finite vorticity induced by actuator curves of arbitrary shape. An actuator curve is an infinitesimally thin region containing a body force density acting on the flow, while the rest of the flow is force‐free. The approach can be used for any flow satisfying this description, but, like other actuator methods, it is naturally suited for modeling turbines or propellers. We derive a weak formulation of the governing equations in the Lagrange streamfunction and solve it using finite elements. Compared to related methods such as the actuator cylinder (AC) approach, our formulation is uniquely suited for computations involving wake–wake or wake–turbine interactions. We validate the method by computing the flow through a single Darrieus vertical‐axis wind turbine (VAWT) and comparing with previous work. To demonstrate the ability to simulate interacting actuators of arbitrary configuration, we simulate a three‐VAWT array. The turbines are modeled in a freestream, and the loading is chosen to represent ideal airfoils. The standard VAWT results are consistent with previous work, validating the method. The three‐VAWT array demonstrates a higher efficiency than the single VAWT (0.56 vs. 0.52), with differing optmal tip speed ratios for the upwind and downwind turbines (upwind: 3.9, downwind: 3.1. The optimum for a single turbine is 3.6). The flow field of the three‐VAWT array shows expected features such as an acceleration of flow between the two counter‐rotating upwind turbines.

Two-stage optimization of three and four straight-bladed vertical axis wind turbines (SB-VAWT) based on Taguchi approach

This research uses computational fluid dynamics (CFD) to perform a two-stage optimization of power output in multiple vertical-axis wind turbines (VAWT) with straight blades. In the first stage, four configurations are evaluated and optimized utilizing the Taguchi approach. Three operational factors, including the distance between the third turbine and the y-axis (H), the distance between the second turbine and the third turbine (B) and, placing the fourth turbine along with two levels, are considered to account for their effects on the output of the multiple turbine system. The impacts of the three factors on the performance are highlighted by H > B > placing the fourth turbine. Subsequently, based on the Taguchi-optimized combination, the analysis of the specific factor is conducted in the second stage by varying the B value. The results suggest that B = 6m without placing the fourth turbine can further intensify the power output of the VAWT system by around 3%, increasing the mean power coefficient (Cp¯) from 0.5026 to 0.5174. This is attributed to the Magnus effect, originating from the first and the second turbine. Furthermore, the results also show that changing the rotating direction of the third turbine from counterclockwise to clockwise deteriorates the output power, reducing the Cp¯ to 0.3339. Overall, the mean power coefficient of the optimized three-turbine system is higher than that of the single VAWT (Cp = 0.4473) by a factor of 15.7% under the wind speed of 8 m⋅s−1 and a tip speed ratio of 2. This reveals that the optimal design can effectively increase the output power performance of VAWT systems.

A Computational Fluid Dynamics Study of an Integrating Savonius-Darrieus Vertical Axis Wind Turbine

To combine the advantages of performance of both Savonius and Darrieus wind turbines, this paper aims to study computationally a novel design configuration of a Vertical Axis Wind Turbine (VAWT). The new design would help cover a broad range of performance parameters between both types of wind turbines as well as overcome drawbacks of the Savonius type at higher rotational speed. The proposed design is to integrate both of Savonius and straight blade Darrieus wind turbines in a single VAWT design configuration. In this design, the turbine rotor consists of a number of similar NACA0015 airfoil blades set in a particular arrangement. By regulating individual angles of rotor blades, the turbine would work as either Savonius or H-Darrieus VAWT. The turbine could also be set to work at different configurations between those for the Savonius and H-Darrieus ones. The computational results revealed that the performance of the proposed integrating wind turbine would be controlled and optimized to cover the operating range of both of Savonius and Darrieus wind turbines. Besides, the performance of Savonius VAWT would be modified when applying this design. When the proposed design is practically implemented, characteristics of both of Savonius and H-Darrieus based wind turbines would be found in a single design.

Measurements of the wake characteristics of co- and counter-rotating twin H-rotor vertical axis wind turbines

Increasing the efficiency of individual vertical-axis wind turbines (VAWTs) has been the subject of much research. However, wind farms that comprise individual VAWTs are not necessarily the most efficient configuration in accordance with VAWTs’ signature wake pattern. This study aims to identify efficient array configurations and thereby increase the packing density and power output by grouping individual VAWTs as a unit. Systematic measurements of wake aerodynamics of co-rotating and counter-rotating (forward- and backward-rotating) twin VAWTs were taken in a wind tunnel. The wake was measured both along the blade mid-span plane up to 10 turbine diameters (10D) and along the vertical plane. The wake of co-rotating twin VAWTs showed great asymmetry, similar to that of a single VAWT. Interestingly, the wake of counter-rotating twin VAWTs demonstrated elegant symmetric patterns. Two pairs of stationary counter-rotating vortices were found to evolve in the wake. The turbulence intensity downstream was observed to experience drastic changes and slow recovery compared with its velocity counterpart. Finally, two types of array units are proposed for applications in wind farms in accordance with the measurements.

Simulation and wake analysis of a single vertical axis wind turbine

AbstractBecause of several design advantages and operational characteristics, particularly in offshore farms, vertical axis wind turbines (VAWTs) are being reconsidered as a complementary technology to horizontal axial turbines. However, considerable gaps remain in our understanding of VAWT performance since cross‐flow rotor configurations have been significantly less studied than axial turbines. This study examines the wakes of VAWTs and how their evolution is influenced by turbine design parameters. An actuator line model is implemented in an atmospheric boundary layer large eddy simulation code, with offline coupling to a high‐resolution blade‐scale unsteady Reynolds‐averaged Navier–Stokes model. The large eddy simulation captures the turbine‐to‐farm scale dynamics, while the unsteady Reynolds‐averaged Navier–Stokes captures the blade‐to‐turbine scale flow. The simulation results are found to be in good agreement with three existing experimental datasets. Subsequently, a parametric study of the flow over an isolated VAWT, carried out by varying solidities, height‐to‐diameter aspect ratios and tip speed ratios, is conducted. The analyses of the wake area and velocity and power deficits yield an improved understanding of the downstream evolution of VAWT wakes, which in turn enables a more informed selection of turbine designs for wind farms. Copyright © 2016 John Wiley & Sons, Ltd.

A Large-Eddy Simulation Study of Vertical Axis Wind Turbine Wakes in the Atmospheric Boundary Layer

In a future sustainable energy vision, in which diversified conversion of renewable energies is essential, vertical axis wind turbines (VAWTs) exhibit some potential as a reliable means of wind energy extraction alongside conventional horizontal axis wind turbines (HAWTs). Nevertheless, there is currently a relative shortage of scientific, academic and technical investigations of VAWTs as compared to HAWTs. Having this in mind, in this work, we aim to, for the first time, study the wake of a single VAWT placed in the atmospheric boundary layer using large-eddy simulation (LES). To do this, we use a previously-validated LES framework in which an actuator line model (ALM) is incorporated. First, for a typical three- and straight-bladed 1-MW VAWT design, the variation of the power coefficient with both the chord length of the blades and the tip-speed ratio is analyzed by performing 117 simulations using LES-ALM. The optimum combination of solidity (defined as N c / R , where N is the number of blades, c is the chord length and R is the rotor radius) and tip-speed ratio is found to be 0.18 and 4.5, respectively. Subsequently, the wake of a VAWT with these optimum specifications is thoroughly examined by showing different relevant mean and turbulence wake flow statistics. It is found that for this case, the maximum velocity deficit at the equator height of the turbine occurs 2.7 rotor diameters downstream of the center of the turbine, and only after that point, the wake starts to recover. Moreover, it is observed that the maximum turbulence intensity (TI) at the equator height of the turbine occurs at a distance of about 3.8 rotor diameters downstream of the turbine. As we move towards the upper and lower edges of the turbine, the maximum TI (at a certain height) increases, and its location moves relatively closer to the turbine. Furthermore, whereas both TI and turbulent momentum flux fields show clear vertical asymmetries (with larger magnitudes at the upper wake edge compared to the ones at the lower edge), only slight lateral asymmetries were observed at the optimum tip-speed ratio for which the simulations were performed.

Wake structure of a single vertical axis wind turbine

The wake structure behind a vertical axis wind turbine (VAWT) is both measured in a wind tunnel using particle imaging velocimetry (PIV) and computed with large-eddy simulation (LES). Geometric and dynamic conditions are closely matched to typical applications of VAWTs (ReD ∼ 1.8 × 105). The experiments and computations were highly coordinated with continuous two-way feedback to produce the most insightful results. Good qualitative agreement is seen between the computational and experimental results. The dependence of the wake structure on the tip speed ratio, TSR, is investigated, showing higher asymmetry and larger vortices at the lower rotational speed, due to stronger dynamic stall phenomena. Instantaneous, ensemble-averaged and phase-averaged fields are discussed, as well as the dynamics of coherent structures in the rotor region and downstream wake.

Aerodynamic Simulation of Vertical-Axis Wind Turbines

Full-scale, 3D, time-dependent aerodynamics modeling and simulation of a Darrieus-type vertical-axis wind turbine (VAWT) is presented. The simulations are performed using a moving-domain finite-element-based ALE-VMS technique augmented with a sliding-interface formulation to handle the rotor-stator interactions present. We simulate a single VAWT using a sequence of meshes with increased resolution to assess the computational requirements for this class of problems. The computational results are in good agreement with experimental data. We also perform a computation of two side-by-side counterrotating VAWTs to illustrate how the ALE-VMS technique may be used for the simulation of multiple turbines placed in arrays.