Offshore Vertical Axis Wind Turbine Research Articles

Parameter optimization method of contra-rotating vertical axis wind turbine: Based on numerical simulation and response surface

In recent years, the depletion of oil resources and increased in air pollution have become the two most serious challenges in the world. Therefore, the offshore vertical axis wind turbine (VAWT) has become a subject of increasing scholarly interest. However, the instability problem of VAWT has become an important reason that limits its continued development. Contra-rotating vertical axis wind turbines (CRVAWT) can improve the recovery efficiency of wind energy and improve the stability of wind turbines. However, the research on simulation analysis and parameter optimization of CRVAWT is not perfect, and further research is needed. This study first performed a numerical simulation of an isolated VAWT using STAR CCM + simulation software and compared the simulation results with wind tunnel tests to verify the accuracy of the model. After that, simulated and comparatively analyzed the proposed CRVAWT. The results indicated that the CRVAWT exhibits a lower power coefficient but better stability than the isolated VAWT. Then, simulations and analyses were conducted on the pitch angle, relative airfoil thickness, rotor spacing, and included angle of the CRVAWT. Finally, a four-parameter, three-level response surface optimization scheme was established using Design-Expert to optimize the blade parameters and obtain the optimal configuration of the contra-rotating wind turbine parameters. After optimization, the power coefficient (Cp) of the CRVAWT is 0.1837, which is 36.68% more than the Cp of pre-optimization and reaches 99.19% of the Cp of the isolated VAWT. And the total torque of the turbine is reduced by 96.96%, which provides a significant stability advantage.

Strategy for mitigating wake interference between offshore vertical-axis wind turbines: Evaluation of vertically staggered arrangement

Wake interference between wind turbines potentially decreases the power output of offshore wind farms. While the staggered arrangement shows promise for mitigating this interference, the understanding of the impact of vertically staggered setup remains ambiguous, especially in the case of vertical-axis wind turbines (VAWTs). Also, the difference between horizontally and vertically staggered arrangements needs to be clarified. This study aims to shed light on these ambiguities, systematically evaluating the effectiveness of vertically staggered arrangement in mitigating wake interference between offshore VAWTs. High-fidelity computational fluid dynamics simulations are used to investigate the wake interference between two vertically staggered MW-class VAWTs. Typical separation distances (3D ≤ LS ≤ 7D) and different vertically staggered distances (−0.25H ≤ LV ≤ 0.75H) are considered, where D and H denote the turbine diameter and blade span length, respectively. Employing the Taguchi method, the effectiveness of horizontally and vertically staggered arrangements is compared, and the relatively optimal layout of the turbine array is identified. The results show that the vertically staggered arrangement significantly improves the power performance of the downstream turbine, e.g., the power output increases by 75.96% when LS = 7D and LV = 0.25H. When dealing with smaller LS (e.g., 3D), a negative LV is suggested, which reduces the tower cost while preserving the performance improvement. The vertically staggered arrangement has a greater impact on wake interference than the horizontally staggered arrangement. In terms of the relatively optimal layout, the power output of the turbine array is increased by 46.27%. These findings would contribute to the layout design of offshore wind farms.

Advancements in Offshore Vertical Axis Wind Turbines

In the past few years, the journal Energies received various original research manuscripts on offshore vertical axis wind turbines (VAWTs) [...]

Modal dynamics and flutter analysis of floating offshore vertical axis wind turbines

Floating platforms provide vertical axis wind turbines (VAWTs) significant advantages over offshore horizontal axis wind turbines, which has led to increased research interest in offshore VAWT technology. This paper examines dynamic stability of floating VAWTs and presents structural dynamic and aero-elastic flutter analysis of utility-scale 5 MW floating VAWTs by coupling a rotor finite element model with a linearized model for the floating system. The coupled floating VAWT model is utilized to study the effects of tower height, number of blades, blade tapering scheme, and impacts of the floating platform on modal properties and flutter. The study provides important new results and guidance to floating VAWT designers: (1) tower height increase leads to lower tower frequencies more prone to resonance, (2) by moving from land-based foundations to a floating TLP foundation, tower-mode frequency is increased significantly (by 49%–68%) which mitigates resonance and increases the flutter RPM (154% increase), (3) increasing the number of blades reduces the tower mode frequencies for both land-based and floating configuration, and (4) blade chord tapering can have a significant impact on increasing the tower mode flutter RPM. Further, analysis of low-frequency rigid body modes shows a safe, higher flutter RPM relative to the operating RPM.

Review of renewable energy sources and offshore wind turbine technology

This paper is a state-of-the-art that aims to highlight all the new developments for wind renewable energy sources, wind turbine system, vertical axis wind turbine and the included components to find the best solution for an offshore vertical axis wind turbine that supplies ships with energy in the outer harbor. This review could help to understand the potential future choices in the design of vertical-axes wind turbine in order to reduce pollution in marine environment.

Floating Offshore Vertical Axis Wind Turbines: Opportunities, Challenges and Way Forward

The offshore wind sector is expanding to deep water locations through floating platforms. This poses challenges to horizontal axis wind turbines (HAWTs) due to the ever growing size of blades and floating support structures. As such, maintaining the structural integrity and reducing the levelised cost of energy (LCoE) of floating HAWTs seems increasingly difficult. An alternative to these challenges could be found in floating offshore vertical axis wind turbines (VAWTs). It is known that VAWTs have certain advantages over HAWTs, and in fact, some small-scale developers have successfully commercialised their onshore prototypes. In contrast, it remains unknown whether VAWTs can offer an advantage for deep water floating offshore wind farms. Therefore, here we present a multi-criteria review of different aspects of VAWTs to address this question. It is found that wind farm power density and reliability could be decisive factors to make VAWTs a feasible alternative for deep water floating arrays. Finally, we propose a way forward based on the findings of this review.

Numerical Analysis and Parameter Optimization of J-Shaped Blade on Offshore Vertical Axis Wind Turbine

In this study, the performance of offshore wind turbines at low tip speed ratio (TSR) is studied using computational fluid dynamics (CFD), and the performance of offshore wind turbines at low tip speed ratio (TSR) is improved by revising the blade structure. First, the parameters of vertical axis offshore wind turbine are designed based on the compactness iteration, a CFD simulation model is established, and the turbulence model is selected through simulation analysis to verify the independence of grid and time step. Compared with previous experimental results, it is shown that the two-dimensional simulation only considers the plane turbulence effect, and the simulation turbulence effect performs more obviously at a high tip ratio, while the three-dimensional simulation turbulence effect has well-fitting performance at high tip ratio. Second, a J-shaped blade with optimized lower surface is proposed. The study showed that the optimized J-shaped blade significantly improved its upwind torque and wind energy capture rate. Finally, the performance of the optimized J-blade offshore wind turbine is analyzed.

Dynamic analysis of a tri-floater with vertical axis wind turbine supported at its centroid

The paper deals with the dynamic analysis of a tri-floater with a 1 MW offshore Vertical Axis Wind Turbine (VAWT) placed at its centroid. Six line catenary mooring system was used for controlling the horizontal movement of the floater. The floater was modeled as a rigid body with six degrees of freedom. Mass, damping and hydrostatic stiffness were calculated by using hydrostatic stability condition. The aerodynamic load on Vertical Axis Wind Turbine was calculated via the stream tube theory. Wave profile was calculated using Airy’s wave theory followed by the use of Morison’s equation to determine the inertial and drag forces on the floater. A computer program was developed by using the MatLab package for force calculation including wind and wave excitations as a dynamic analysis. The Newmark - beta method was performed for these analyses. The equation of motion for the floater was solved in time domain. Restoring force by mooring lines at each instant of time was calculated based on the cable profile. Responses of the tri-floater with VAWT in different sea conditions were analyzed. It was proven that surge, heave and pitch are the predominant motions for a straight (00) wave. These motions were also analyzed for the waves with different inclinations and their responses were also considered and compared.

Structural analysis of an offshore vertical axis wind turbine composite blade experiencing an extreme wind load

The vertical axis wind turbine (VAWT) configuration has many advantages for an offshore wind turbine installation. The VAWT is omnidirectional and its rotating mechanical components can be placed close to sea level. In this paper, the structural analysis of a VAWT blade structure subject to a critical load case was investigated with two methods, an analytical model and a finite element (FE) model. It was shown that the utilisation of a composite blade topology can resist the induced flapwise loading and the material strains were contained within their allowable limits. The analytical approach was demonstrated to be a quick and accurate technique to compute the composite blade strain distribution when compared to the FE model results.

Multiphysics simulations of the dynamic and wakes of a floating Vertical Axis Wind Turbine

A framework performing Large Eddy Simulations of the flow past Floating Offshore Vertical Axis Wind Turbines (FOVAWT) mounted on semi-submersible platforms is presented. The simulation tool captures the unsteady flow and the resolved 6-DOF motion of the system. A state-of-the-art vortex particle-mesh method solves the aerodynamics and wakes of the turbines. The hydrodynamic loads are accounted for via the relative form of the Morison’s equations while the mooring lines tension is computed through a lumped-mass model. Realistic conditions are further obtained by introducing a sheared turbulent inflow and erratic waves in a simulation domain that extends ten diameters downstream of the machine. First, analyses of an isolated FOVAWT wake and motion are performed and the impact of prominent environmental phenomena is assessed. In a second step, the interactions of two FOVAWTs throughout their wakes are studied. In general, the incoming wake signature induces larger oscillation of the downstream machine, alters the shape of the wakes and shortened the transition to turbulence.

Unsteady effects on a pitching airfoil at conditions relevant for large vertical axis wind turbines

Interest in offshore vertical axis wind turbines (VAWTs) has created a need to study VAWTs at much higher Reynolds numbers than they have previously been studied at. VAWTs are characterised by unsteady aerodynamics, and high Reynolds numbers have the potential to alter the blade aerodynamics significantly. Here, results are reported on an airfoil that is pitched sinusoidally around zero angle of attack at Rec = 1 × 106, at a reduced frequency k = 0.15 and amplitudes of 5° < α < 20°. Since the static stall angle is not exceeded, no stall effects occur. Nevertheless, lift, drag and moment coefficients show noticeable hysteresis. Despite the high amplitudes of oscillation, lift and moment coefficients show reasonable agreement with unsteady aerodynamic theories by Theodorsen and Motta et al. with regard to the width of the hysteresis loops, but have noticeably steeper slopes.

Studying Ways to Improve Bay Waste Management Using Floating Off-shore Vertical Axis Wind Turbines

In recent years, on the problem of environmental pollution caused by suspended garbage in coasts and bays, sedimented sludge and milliplastics have a serious impact on the environment. In particular, hypoxia caused by eutrophication in the bay is a factor that deteriorates aquaculture productivity. In this study, we developed a helical pump driven by a floating vertical axis wind turbine that can be moored and towed by a ship, and proposed a method of removing the slurried volume of sediment from the sea floor by removing it. Therefore, we report the results of an experiment to investigate the pumping performance of the helical screw pump with respect to the suction capacity.

Two-Dimensional Computational Fluid Dynamics Study on the Performance of Twin Vertical Axis Wind Turbine With Deflector

Abstract The offshore wind industry is undergoing a rapid development due to its advantage over the onshore wind farm. The vertical axis wind turbine (VAWT) is deemed to be potential in offshore wind energy utilization. A design of the offshore vertical axis wind turbine with a deflector is proposed and studied in this paper. Two-dimensional computational fluid dynamics (CFD) simulation is employed to investigate the aerodynamic performance of wind turbine. An effective method of obtaining the blade’s angle of attack (AoA) is introduced in CFD simulation to help analyze the blade aerodynamic torque variation. The numerical simulations are validated against the measured torque and wake velocity, and the results show a good agreement with the experiment. It is found that the blade instantaneous torque is correlated with the local AoA. Among the three deflector configurations, the front deflector leads to favorable local flow for the blade, which is responsible for the improved performance.

Fundamental Experiment about the Environmental Improvement in the Gulf using a Floating Offshore Vertical Axis Wind Turbine

Fundamental Experiment about the Environmental Improvement in the Gulf using a Floating Offshore Vertical Axis Wind Turbine

Optimisation of design and operation of generators for offshore vertical axis wind turbines

AbstractA process for optimizing both the design and operation of the generator for a large offshore vertical axis wind turbine (VAWT) is developed. The objectives of the optimization process are to minimize additional costs and losses in the generator to allow for a fair evaluation of the impact of the VAWT environment on the powertrain. A spectrum of torque control strategies was tested based on the ratio, q, of the allowed electrical torque variation to the inherent mechanical torque variation. Equations relating q to the generator losses were established. The effect of q on the energy extracted by the rotor was also investigated and incorporated into the optimization process. This work shows that a variable q strategy with respect to wind speed can improve turbine performance across the range of operational wind speeds depending on the torque loading from the rotor blades. In turn, this also allows for the torque rating of the generator to be reduced from the peak torque rating that would otherwise be expected, creating an opportunity to downscale the generator size, reducing costs. The optimization of powertrain design and operation should be carried out at as high level as is possible, ideally using the fully factored cost of energy (COE) to guard against unexpected losses because of excessive focus in one COE factor (for example reducing upfront cost but in turn reducing availability).

On mooring line tension and fatigue prediction for offshore vertical axis wind turbines: A comparison of lumped mass and quasi-static approaches

Despite several potential advantages, relatively few studies and design support tools have been developed for floating vertical axis wind turbines. Due to the substantial aerodynamics differences, the analyses of vertical axis wind turbine on floating structures cannot be easily extended from what have been already done for horizontal axis wind turbines. Therefore, the main aim of the present work is to compare the dynamic response of the floating offshore wind turbine system adopting two different mooring dynamics approaches. Two versions of the in-house aero-hydro-mooring coupled model of dynamics for floating vertical axis wind turbine (FloVAWT) have been used, employing a mooring quasi-static model, which solves the equations using an energetic approach, and a modified version of floating vertical axis wind turbine, which instead couples with the lumped mass mooring line model MoorDyn. The results, in terms of mooring line tension, fatigue and response in frequency have been obtained and analysed, based on a 5 MW Darrieus type rotor supported by the OC4-DeepCwind semisubmersible.

Conceptual design of a large-scale floating offshore vertical axis wind turbine

Large-scale floating vertical axis wind turbines (VAWTs) are an attractive and economical solution to harness superior offshore wind resources in deep water locations. This paper presents the conceptual design of a VAWT for this application using a developed aerodynamic modelling strategy. A comprehensive examination of several critical VAWT design parameters was undertaken which included the turbine solidity, blade number, blade aspect ratio and non-prismatic strut design.This study identified a low solidity turbine (σ = 0.263) gave the best aerodynamic performance, while a two-bladed VAWT design is recommended. The results also indicated a blade aspect ratio in the range 10 ≥ H/c ≥ 20 gives favorable performance. Finally, the geometrical details and operating specifications for a 5 MW VAWT design are presented.

Dynamic Analysis of a Truss Spar-Type Floating Foundation for 5 MW Vertical-Axis Wind Turbine

This paper studies the dynamic characteristic of the truss Spar-type floating foundation used to support the offshore vertical-axis wind turbine (VAWT). The effects of changes in foundation structural parameters on its motions were evaluated. The results show that radius of the buoyancy tank, radius of the upper mechanical tank, interval of the center of gravity and center of buoyancy, and height of the upper mechanical tank have important effects on the heave and pitch motions of the foundation. Two sets of foundation parameters (FS-1 and FS-2) were selected to support the 5 MW Darrieus wind turbine. The motion performances of the two floating VAWTs, S-1 (the VAWT supported by FS-1) and S-2 (the VAWT supported by FS-2), were analyzed and compared. It was observed that the amplitudes of the heave and pitch motions of the floating VAWT depend on the wave loads; the mean values of the heave and pitch motions depend on the aerodynamic loads. The floating VAWT S-2 had better motion performance; its heave and pitch motions were all small. The heave frequencies of the floating VAWT were equal to the wave frequencies. For the pitch frequencies, there is a component of the rotor rotational frequency (0.175 Hz) for cases LC1 to LC4, while the amplitudes of the twice-per-revolution (2P) response are far smaller than the amplitudes of the wave response.

Effect of Turbulence Intensity on the Performance of an Offshore Vertical Axis Wind Turbine

Offshore wind energy is one of the most competitive renewable energy resources available to us, which until now been under- exploited. Most of the problems associated with wind farm installation like land acquisition, low wind conditions and its visual impact can be eliminated to large extent by going offshore. In fact it is expected that by the year 2020, 40GW of offshore wind power capacity will be in operation. In an offshore context the wind turbine design methodologies have to address new challenges. For optimal performance the turbine needs to be huge in size and for horizontal axis wind turbines (HAWT) the diameter has already reached a size of 200m. Till now little attention has been paid to vertical axis offshore wind turbines. However, within the NOWITECH project new concepts for vertical axis turbine have been proposed and it might not take a long time before such turbines may become an realistic alternative for use offshore. The current work characterizes variable turbulence intensity flow field around a rotating vertical axis wind turbine (VAWT) in an offshore context. Complete three dimensional numerical transient simulations are performed accounting for the variation of multiple turbulence intensity levels associated with the oncoming wind. Usually offshore winds are highly turbulent in nature partially because of the rapid changes in wind directions along with the sea-air interaction. The results from the study indicate that due to the increase in the turbulence intensity level of 5% to 25% the performance of wind turbine decreases by almost 23% to 42% compared to no turbulence in the incoming wind field.

Conceptual design of a floating support structure for an offshore vertical axis wind turbine: the lessons learnt

The design of floating support structures for wind turbines located offshore is a relatively new field. In contrast, the offshore oil and gas industry has been developing its technologies since the mid 1950s. However, the significantly and subtly different requirements of the offshore wind industry call for new methodologies. An Energy Technologies Institute (ETI) funded project called NOVA (for Novel Vertical Axis wind turbine) examined the feasibility of a large offshore vertical axis wind turbine in the 10–20 MW power range. The development of a case study for the NOVA project required a methodology to be developed to select the best configuration, based on the system dynamics. The design space has been investigated, ranking the possible options using a multi-criteria decision making (MCDM) method called TOPSIS. The best ‘class’ or design solution (based on water plane area stability) has been selected for a more detailed analysis. Two configurations are considered: a barge and a semi-submersible. The iterations to optimise and compare these two options are presented here, taking their dynamics and costs into account. The barge concept evolved to the ‘triple doughnut-Miyagawa’ concept, consisting of an annular cylindrical shape with an inner (to control the damping) and outer (to control added mass) bottom flat plates. The semi-submersible was optimised to obtain the best trade-off between dynamic behaviour and amount of material needed. The main conclusion is that the driving requirement is an acceptable response to wave action, not the ability to float or the ability to counteract the wind turbine overturning moment. A simple cost comparison is presented.