Showing papers on "Tip-speed ratio published in 2017"
TL;DR: In this article, the authors investigated the variations in loads and moments on the turbine as well as the experienced angle of attack, shed vorticity and boundary layer events (leading edge and trailing edge separation, laminar-to-turbulent transition) as a function of pitch angle.
262 citations
TL;DR: In this paper, the effect of the domain size and azimuthal increment on the performance of a 2-bladed VAWT operating at a moderate tip speed ratio of 4.5 using 2-dimensional and 2.5-dimensional simulations with the unsteady Reynolds-averaged Navier-Stokes (URANS).
192 citations
TL;DR: In this article, a review of recent published works on CFD simulations of Darrieus VAWTs is presented for turbulence modeling, spatial and temporal discretization, numerical schemes and algorithms, and computational domain size.
141 citations
TL;DR: In this paper, a CFD study is conducted in order to characterize the dynamic behavior of a Savonius vertical axis wind turbine, which is executed using the open source code, OpenFOAM.
114 citations
TL;DR: In this article, the power output of two straight-bladed vertical-axis wind turbines is simulated using computational fluid dynamics (CFD) as well as analyzed and optimized using the Taguchi method.
108 citations
TL;DR: In this paper, the authors proposed a novel system of ducted nozzle configuration around the Savonius rotor to increase the efficiency of the turbine, and the maximum power coefficient of the ducted turbine was increased by 78% compared to the conventional modified rotor.
98 citations
TL;DR: In this article, a non-standard extended Kalman filter was used to estimate the TSR and pitch angle of a variable-speed wind turbine for an industrial baseline controller to maximize the maximum power extraction (MPE) of the turbine.
90 citations
TL;DR: In this paper, the effect of rotor aspect ratio and solidity on the power performance of straight-bladed VAWT was investigated in three-dimensional analysis by panel method based on the assumption of an incompressible and potential flow coupled with a free vortex wake.
76 citations
TL;DR: In this paper, the effect of channel blockage on the performance of axial and cross-flow turbines with the objective of filling a gap in the literature on suitable blockage corrections for crossflow turbines was investigated.
69 citations
TL;DR: In this paper, a detailed experimental investigation of the wake propagation behind a horizontal axis turbine with three blades was conducted in a recirculating water flume, where an Acoustic Doppler Velocimeter was employed to measure the time varying velocities at fifteen depths across the width of the open flume to obtain the threedimensional velocity and turbulence fields within the length of 20 Rotor Diameters downstream.
62 citations
TL;DR: In this article, the influence of the platform surge motion on the behaviors of the power output and rotor thrust of a typical Spar-type OFWT were investigated using Free Vortex Method (FVM).
TL;DR: In this paper, the authors investigate the flow development of a single bladed vertical axis wind turbine using Computational fluid dynamics (CFD) methods and demonstrate that the turbine is observed to generate negative power at certain azimuth angles.
Abstract: The aim of this study is to investigate the flow development of a single bladed vertical axis wind turbine using Computational fluid dynamics (CFD) methods. The blade is constructed using the NACA 0012 profile and is operating under stalled conditions at tip speed ratio of 2. Two dimensional simulations are performed using a commercial CFD package, ANSYS Fluent 15.0, employing the Menter-SST turbulence model. For the preliminary study, simulations of the NACA 0012 airfoil under static conditions are carried out and compared with available measurement data and calculations using the boundary layer code XFOIL. The CFD results under the dynamic case are presented and the resulting aerodynamic forces are evaluated. The turbine is observed to generate negative power at certain azimuth angles which can be divided into three main zones. The blade vortex interaction is observed to strongly influence the flow behavior near the blade and contributes to the power production loss. However, the impact is considered small since it covers only 6.4 % of the azimuth angle range where the power is negative compared to the dynamic stall impact which covers almost 22 % of the azimuth angle range.
TL;DR: In this article, a lamped mass dynamic model with 14 degrees of freedom was developed for the Darrieus turbine bevel spur gear subjected to transient aerodynamic loads, and the aerodynamic torque was obtained by solving the two dimensional unsteady incompressible Navies Stocks equation with the k- ω shear stress transport turbulence model.
TL;DR: In this article, an artificial neural network based particle swarm optimization has been trained offline to learn the characteristic of the turbine power as a function of wind and machine speeds, and then it has been realized online to estimate the varying wind speed.
Abstract: This paper proposes a maximum power point tracking (MPPT) technique based on the tip speed ratio control for small scale wind turbines (WTs). In this paper, artificial neural network based particle swarm optimization has been trained offline to learn the characteristic of the turbine power as a function of wind and machine speeds. Afterwards, it has been realized online to estimate the varying wind speed. It is essential to design a controller that can track the maximum peak of energy regardless of wind speed changes. Therefore, this work provides a novel robust direct adaptive fuzzy–Proportional-Integral (PI) controller during the MPPT process through tuning duty cycle of the boost converter for permanent magnet synchronous generator driven by a WT. The proposed method has successfully decreased the ripples of coefficient of power (Cp) which is the index of MPPT mode, under variations of the wind speed in comparison with conventional controller. Finally, a systematic analysis is presented which is in goo...
TL;DR: In this article, the effects of a passive flow control method on aerodynamic performance of a HAWT by splitting its blades along the span were numerically investigated, and the results revealed that for an attached flow, torque value are sensitively dependent upon split location and injected flow angle.
TL;DR: In this article, aero-acoustic computational study that investigates the noise caused by one of the most promising wind energy conversion concepts, namely the "Wind-Lens" technology is presented.
TL;DR: A novel control algorithm based on adaptive neuro-fuzzy inference system (ANFIS) is proposed to estimate the wind turbine power coefficient as a function of tip-speed ratio and pitch angle and results show the effectiveness of the proposed model.
TL;DR: In this paper, a 2D flow field simulation of a helical vertical axis wind turbine (HVAWT) with four blades has been carried out by means of a large eddy simulation (LES).
Abstract: Vertical axis wind turbines (VAWTs) are gradually receiving more and more interest due to their lower sensitivity to the yawed wind direction. Compared with straight blades VAWT, blades with a certain helicity show a better aerodynamic performance and less noise emission. Nowadays computational fluid dynamics technology is frequently applied to VAWTs and gives results that can reflect real flow phenomena. In this paper, a 2D flow field simulation of a helical vertical axis wind turbine (HVAWT) with four blades has been carried out by means of a large eddy simulation (LES). The power output and fluctuation at each azimuthal position are studied with different tip speed ratio (TSR). The result shows that the variation of angle of attack (AOA) and blade-wake interaction under different TSR conditions are the two main reasons for the effects of TSR on power output. Furthermore, in order to understand the characteristics of the HVAWT along the spanwise direction, the 3D full size flow field has also been studied by the means of unsteady Reynold Averaged Navier-Stokes (U-RANS) and 3D effects on the turbine performance can be observed by the spanwise pressure distribution. It shows that tip vortex near blade tips and second flow in the spanwise direction also play a major role on the performance of VAWTs.
TL;DR: In this article, a numerical method was adopted to investigate the effects of different winglet configurations on turbine performance, especially focusing on the direction for the winglet tip to point towards (the suction side, pressure side or both sides of the main blade).
TL;DR: In this article, a two-bladed vertical axis wind turbine operating at a wind speed of 8 m/s for tip speed ratios (λ) of 0.50-3.0 was investigated.
Abstract: Computational fluid dynamics (CFD) studies are carried out on a two-bladed vertical axis wind turbine operating at a wind speed of 8 m/s for tip speed ratios (λ) of 0.50–3.0. The blade is the NACA0021 airfoil with chord length 0.265 m and rotor radius 1 m. Basic sensitivity studies for various time step sizes are carried out. The results are validated against available measurement data from the literature. Excellent agreement is obtained for small λ up to optimum condition. For the higher tip speed ratios, the two-dimensional CFD computations predict higher results than the wind tunnel experiment, but they are very similar to the field measurement data. Wake characteristics are presented, showing that the wake becomes Gaussian at 5 times radius downstream of the rotor. It is shown that complex flow phenomena occur owing to dynamic stall onset, especially for the smaller tip speed ratio.
TL;DR: In this paper, a revised theoretical analysis of aerodynamic optimization of horizontal-axis wind turbines, including drag effects, based on Blade Element Momentum theory, is presented, and it is demonstrated that horizontal axis wind turbines can never reach Betz limit, even in the absence of drag effects.
TL;DR: In this paper, the authors investigated the performance of the tip speed ratio (TSR) and optimal torque (OT) control methods under different wind speed characteristics on a 1.5 MW wind turbine model.
Abstract: Variable speed wind turbines (VSWTs) usually adopt a maximum power point tracking (MPPT) method to optimize energy capture performance. Nevertheless, obtained performance offered by different MPPT methods may be affected by the impact of wind turbine (WT)’s inertia and wind speed characteristics and it needs to be clarified. In this paper, the tip speed ratio (TSR) and optimal torque (OT) methods are investigated in terms of their performance under different wind speed characteristics on a 1.5 MW wind turbine model. To this end, the TSR control method based on an effective wind speed estimator and the OT control method are firstly presented. Then, their performance is investigated and compared through simulation test results under different wind speeds using Bladed software. Comparison results show that the TSR control method can capture slightly more wind energy at the cost of high component loads than the other one under all wind conditions. Furthermore, it is found that both control methods present similar trends of power reduction that is relevant to mean wind speed and turbulence intensity. From the obtained results, we demonstrate that, to further improve MPPT capability of large VSWTs, other advanced control methods using wind speed prediction information need to be addressed.
19 Jun 2017
TL;DR: In this paper, a vortex particle-mesh (VPM) method with immersed lifting lines was developed and validated for large-eddy simulation of vertical axis wind turbine (VAWT) flows.
Abstract: . A vortex particle-mesh (VPM) method with immersed lifting lines has been developed and validated. Based on the vorticity–velocity formulation of the Navier–Stokes equations, it combines the advantages of a particle method and of a mesh-based approach. The immersed lifting lines handle the creation of vorticity from the blade elements and its early development. Large-eddy simulation (LES) of vertical axis wind turbine (VAWT) flows is performed. The complex wake development is captured in detail and over up to 15 diameters downstream: from the blades to the near-wake coherent vortices and then through the transitional ones to the fully developed turbulent far wake (beyond 10 rotor diameters). The statistics and topology of the mean flow are studied. The computational sizes also allow insights into the detailed unsteady vortex dynamics and topological flow features, such as a recirculation region influenced by the tip speed ratio and the rotor geometry.
TL;DR: In this paper, the effects of turbulence intensity and wind shear on the wind turbine wake characteristics were investigated by field experiments, where the authors presented the wind velocity distribution of Horizontal Axis Wind Turbine (HAWT) in the horizontal axis direction.
TL;DR: In this paper, three horizontal axis tidal stream turbines (HATST) with winglets are proposed and investigated to enhance the energy conversion efficiency, and three different winglets including trapezoid, triangle and blended types are equipped on the tip of the blade.
TL;DR: Considering the estimation error of the wake model, a solution to implement the optimized pitch angle and tip speed ratio is proposed, which is to generate the optimal control curves for each individual wind turbine off-line.
Abstract: In modern wind farms, maximum power point tracking (MPPT) is widely implemented. Using the MPPT method, each individual wind turbine is controlled by its pitch angle and tip speed ratio to generate the maximum active power. In a wind farm, the upstream wind turbine may cause power loss to its downstream wind turbines due to the wake effect. According to the wake model, downstream power loss is also determined by the pitch angle and tip speed ratio of the upstream wind turbine. By optimizing the pitch angle and tip speed ratio of each wind turbine, the total active power of the wind farm can be increased. In this paper, the optimal pitch angle and tip speed ratio are selected for each wind turbine by the exhausted search. Considering the estimation error of the wake model, a solution to implement the optimized pitch angle and tip speed ratio is proposed, which is to generate the optimal control curves for each individual wind turbine off-line. In typical wind farms with regular layout, based on the detailed analysis of the influence of pitch angle and tip speed ratio on the total active power of the wind farm by the exhausted search, the optimization is simplified with the reduced computation complexity. By using the optimized control curves, the annual energy production (AEP) is increased by 1.03% compared to using the MPPT method in a case-study of a typical eighty-turbine wind farm.
TL;DR: In this article, a Double Multiple Streamtube model, a free-wake vortex model and RANS CFD simulations are used to predict the performance of the 17m Vertical Axis Wind Turbine, field tested by Sandia National Laboratories.
TL;DR: In this paper, the effects of the main geometrical parameters affecting the aerodynamic performance of the Invelox are numerically studied, including the inlet area, the diameter of the Venturi section, and the height of the funnel on the wind speed increment inside the venturi section.
Abstract: High wind velocities are required for wind projects to be economically efficient. To increase the wind speed, the concept of ducted wind turbines has been introduced in recent decades. Among them is the Invelox, which can capture the wind from all directions and funnel the collected air to the ground level. Primary results have shown that this design can increase the overall efficiency of a wind project. In this study, the effects of the main geometrical parameters affecting the aerodynamic performance of the Invelox are numerically studied. The effects of the inlet area, the diameter of the Venturi section and the height of the funnel on the wind speed increment inside the Venturi section have been determined. Results show that the inlet area and the Venturi cross section area have the most significant effects on the speed ratio (SR) of the Invelox, while the funnel height and air velocity have minor effects. In the case of appropriate selection of the geometry parameters, velocity increments up to 1.9 are achievable. Finally, the effects of adding a horizontal axis wind turbine inside the Venturi on its power coefficient are studied. Results show that Invelox greatly enhances the turbine maximum power coefficient. However, it decreases the tip speed ratio corresponding to the maximum power coefficient.
TL;DR: In this article, a new class of wind turbine termed the external axis wind turbine (EAWT) has been recently developed in response to the anticipated increase in global demand for renewable energy.
TL;DR: In this article, a 3.5 kW wind turbine simulator is designed and manufactured in order to emulate torque response of a 2 MW wind turbine, which consists of a motor, a gear box, a flywheel, and a generator.
Abstract: Small-scale wind turbine simulators have been used in laboratories in order to verify power control of real-world large multi-MW wind turbines. The response speed of multi-MW wind turbines is so slow that the response time considerably exceeds several seconds. This fact should be considered in the design of small-scale wind turbine simulators. In this paper, a 3.5 kW wind turbine simulator is designed and manufactured in order to emulate torque response of a 2 MW wind turbine. The small-scale wind turbine simulator consists of a motor, a gear box, a flywheel, and a generator. Two main design parameters are the rotor radius and the mass moment of inertia of the flywheel. The main design objective is to make the 3.5 kW wind turbine simulator have the similar both time constant and wind speed range for optimal TSR (tip speed ratio) to those of the target 2 MW wind turbine. Through numerical simulations and experiments for step response, we demonstrate that the designed and manufactured 3.5 kW wind turbine simulator has the response speed similar to that of the 2MW wind turbine in the aspect of torque response.