Miniature Wind Turbine Research Articles

Wake meandering statistics of a model wind turbine: Insights gained by large eddy simulations

A numerical investigation of the wake of an axial flow miniature wind turbine is presented to elucidate the three-dimensional structure of the wake and the mechanisms controlling near and far wake instabilities.

Storage of energy harvested from a miniature turbine in a novel organic capacitor

The potential of harvesting energy generated from a (5-cm) miniature wind turbine and storing the charge in a novel organic capacitor is experimentally investigated. The energy is generated by subjecting the wind turbine to different flow speeds between 2 and 8m/s. A maximum output power of 0.2W was attained with an optimum load resistance of 220Ω at 8m/s. The organic capacitor consists of layer-by-layer deposition of synthesized organic semi-conductive polymers, made of doping ionic liquid with non-conductive polymers, and metallic charge element made out of synthesized palladium (Pd) nanoparticles with a diameter of 6nm. Scanning electron microscopy (SEM) images revealed uniformly distributed Pd nanoparticles over the entire substrate. Capacitance–voltage (C–V) measurements were carried out for the fabricated organic capacitor. The results exhibit large window gates that showed that the Pd nanoparticles are responsible for storing the electric charge. The performance of the organic storage device was evaluated through comparison with a commercial capacitor. The results show that the organic capacitor performed much better at lower frequency values. It was also observed the voltage produced at various airflow speeds was high enough to store the harvested energy in the organic capacitor.

Modeling and Experimental Investigation of a Periodically Excited Hybrid Energy-Harvesting Generator

Abstract In this article the modeling of a broadband energy harvester utilizing piezoelectric and electromagnetic effects for rotational applications is presented. The hybrid energy harvester consists of a one-side-clamped piezoelectric bimorph with a solenoid on the free end and is excited periodically but non-harmonically by magnets that are fixed on a rotating object. To estimate and describe the performance of the energy harvester concept a linear semi-analytical model for the bimorph and the solenoid is developed and then enhanced for non-harmonic system oscillations by decomposing them into their harmonic components. A comparison between the calculated and measurement signals of a prototype device shows great conformity. According to model-based and experimental analysis, the hybrid system has good broadband behavior regarding electric power output. That aspect makes the device a perfect energy-harvesting system for application with highly fluctuating revolution speeds like miniature wind turbines.

Miniature Contactless Piezoelectric Wind Turbine

This study presents the development of a miniature wind turbine that can be used for powering wireless sensors deployed at remote locations. The wind turbine utilizes piezoelectric transducers in order to reduce the start-up speed. Six piezoelectric bimorphs with magnetic tip mass were actuated through attractive and repulsive force between permanent magnets. The design and characterization of the prototype is discussed along with a Finite Element Model (FEM) of the piezoelectric elements. The wind turbine was 23 cm high and 16.5 cm wide. It was able to achieve low cut-in speeds of 1m/s providing power outputs ranging between 0.5 mW and 3 mW for wind speeds in the range of 1 m/s to 4 m/s.

Miniature horizontal axis wind turbine system for multipurpose application

A MWT (miniature wind turbine) has received great attention recently for powering WISP (Wireless Intelligent Sensor Platform). In this study, two MHAWTs (miniature horizontal axis wind turbines) with and without gear transmission were designed and fabricated. A physics-based model was proposed and the optimal load resistances of the MHAWTs were predicted. The open circuit voltages, output powers and net efficiencies were measured under various ambient winds and load resistances. The experimental results showed the optimal load resistances matched well with the predicted results; the MHAWT without gear obtained higher output power at the wind speed of 2 m/s to 6 m/s, while the geared MHAWT exhibited better performance at the wind speed higher than 6 m/s. In addition, a DCM (discontinuous conduction mode) buck-boost converter was adopted as an interface circuit to maximize the charging power from MHAWTs to rechargeable batteries, exhibiting maximum efficiencies above 85%. The charging power reached about 8 mW and 36 mW at the wind speeds of 4 m/s and 6 m/s respectively, which indicated that the MHAWTs were capable for sufficient energy harvesting for powering low-power electronics continuously.

Development of a self-contained wireless-based SHM system for monitoring a swing bridge

Structural health monitoring (SHM) based on wireless sensor network (WSN) technology has been introduced into civil infrastructures in recent years due to its advantages of easy and flexible installation, low system cost and increased robustness. The wireless–based SHM system involves a multidisciplinary effort that encompasses a number of synergetic technologies brought together to provide a system that can potentially monitor the structural condition of a structure in real time. In this paper, a WSN for SHM is designed, implemented and tested on a swing Beaufort #25 Bridge at the East Coast of North Carolina. To characterise the dynamic behaviour of the swing bridge, seven wireless sensor nodes are distributed along the 55–m main span, which intended to collect acceleration data from the structure under ambient vibration. The acquisition data will then be stored and sent via the base station to a website, where the user can download these data and display it by a GUI tool. The wireless sensing unit is designed not only for reliable communication of response acceleration measurements but also for self–powered capacity. This study explores two energy harvesting approaches, solar panel and miniature wind turbine, to provide the power demands of the wireless sensor nodes.

Performance Prediction and Demonstration of a Miniature Horizontal Axis Wind Turbine

A miniature wind turbine (MWT) has received great attention recently for powering low-power devices. In this paper, a physics-based comprehensive model for predicting the performance of a miniature horizontal axis wind turbine (MHAWT) was established. The turbine rotor performance was investigated and an approximation of the power coefficient of the turbine rotor was made. Incorporation of the approximation with the equivalent circuit model, which was proposed in accordance with the principles of the MHAWT, in addition to its overall system performance versus the resistive load and ambient wind speed, was predicted. To demonstrate predictive modeling capability, the MHAWT system comprised of commercially available off-the-shelf components was designed and its performance was experimentally tested. The results matched well with those by prediction modeling, which implies that the proposed model holds promise in estimating and optimizing the performance of the MWT.

The going gets tough: Renewable sessions were in evidence at this year's U.S. PowerGen, but the profile of wind and solar was less obvious. Drew Robb went along to find out more.

RENEWABLE ENERGY certainly remains on the agenda at the annual U.S. PowerGen event. Electric vehicles, CSP, offshore wind and hybrid renewable/fossil were combos that remained in the spotlight. And conference tracks included solar, wind and biomass. But while previous PowerGen events have featured miniature wind turbines at the booths of dozens of energy companies – as they sought to highlight their renewable credentials – few windmill displays remain. And the show's renewable pavilion, introduced with a fanfare a few years back, seems to have diminished. While Vestas, Clipper and REpower were in evidence in the beginning, none of the major renewable players appeared to be in evidence. Could it be the wrong message to send out that wind and solar companies prefer their own annual extravaganzas to what is the power industry's marquee event?

Turbulent Flow Properties Around a Staggered Wind Farm

The fundamental properties of turbulent flow around a perfectly staggered wind farm are investigated in a wind tunnel. The wind farm consisted of a series of 10 rows by 2–3 columns of miniature wind turbines spaced 5 and 4 rotor diameters in the streamwise and spanwise directions respectively. It was placed in a boundary-layer flow developed over a smooth surface under thermally neutral conditions. Cross-wire anemometry was used to obtain high resolution measurements of streamwise and vertical velocity components at various locations within and above the wind farm. The results show that the staggered configuration is more efficient in terms of momentum transfer from the background flow to the turbines compared to the case of an aligned wind turbine array under similar turbine separations in the streamwise and spanwise directions. This leads to improved power output of the overall wind farm. A simplified analysis suggests that the difference in power output between the two configurations is on the order of 10%. The maximum levels of turbulence intensity in the staggered wind farm were found to be very similar to that observed in the wake of a single wind turbine, differing substantially with that observed in an aligned configuration with similar spacing. The dramatic changes in momentum and turbulence characteristics in the two configurations show the importance of turbine layout in engineering design. Lateral homogenization of the turbulence statistics above the wind farm allows for the development of simple parametrizations for the adjustment of flow properties, similar to the case of a surface roughness transition. The development of an internal boundary layer was observed at the upper edge of the wind farm within which the flow statistics are affected by the superposition of the ambient flow and the flow disturbance induced by the wind turbines. The adjustment of the flow in this layer is much slower in the staggered situation (with respect to its aligned counterpart), implying a change in the momentum/power available at turbine locations. Additionally, power spectra of the streamwise and vertical velocity components indicate that the signature of each turbine-tip vortex structure persists to locations deep within the wind farm.

Large-Eddy Simulation of Wind-Turbine Wakes: Evaluation of Turbine Parametrisations

Large-eddy simulation (LES), coupled with a wind-turbine model, is used to investigate the characteristics of a wind-turbine wake in a neutral turbulent boundary-layer flow. The tuning-free Lagrangian scale-dependent dynamic subgrid-scale (SGS) model is used for the parametrisation of the SGS stresses. The turbine-induced forces (e.g., thrust, lift and drag) are parametrised using two models: (a) the ‘standard’ actuator-disk model (ADM-NR), which calculates only the thrust force and distributes it uniformly over the rotor area; and (b) the actuator-disk model with rotation (ADM-R), which uses the blade-element theory to calculate the lift and drag forces (that produce both thrust and rotation), and distribute them over the rotor disk based on the local blade and flow characteristics. Simulation results are compared to high-resolution measurements collected with hot-wire anemometry in the wake of a miniature wind turbine at the St. Anthony Falls Laboratory atmospheric boundary-layer wind tunnel. In general, the characteristics of the wakes simulated with the proposed LES framework are in good agreement with the measurements in the far-wake region. The ADM-R yields improved predictions compared with the ADM-NR in the near-wake region, where including turbine-induced flow rotation and accounting for the non-uniformity of the turbine-induced forces appear to be important. Our results also show that the Lagrangian scale-dependent dynamic SGS model is able to account, without any tuning, for the effects of local shear and flow anisotropy on the distribution of the SGS model coefficient.

Research on wind turbine rotor models using NACA profiles

In this study, rotation rates and power coefficients of miniature wind turbine rotor models manufactured using NACA profiles were investigated. For this purpose, miniature rotor models with 310 mm diameter were made from “Balsa” wood. When all properties of rotor models were taken into account, a total of 180 various combinations were obtained. Each combination was coded with rotor form code. These model rotors were tested in a wind tunnel measurement system. Rotation rates for each rotor form were determined based on wind speed. Power coefficient values were calculated using power and tip speed rates of wind. Rotor models produced a rotation rate up to 3077 rpm, with a power coefficient rate up to 0.425. Rotor models manufactured by using NACA 4412 profiles with 0 grade twisting angle, 5 grade blade angle, double blades had the highest rotation rate, while those manufactured by using NACA 4415 profiles with 0 grade twisting angle, 18 grade blade angle, 4 blades had the highest power coefficient.

An Experiment on the Electric Energy Performance of the Wind Turbine Rotors

First of all 270 sets of miniature wind turbine rotors with different properties were produced by using some NACA profiles. The produced 270 sets of rotors of different forms were tested in a wind tunnel. During the test, the electric voltages and the electric currents that each rotor form generated under different wind speeds were measured. Then the performance of each rotor form was laid down in view of such measurements. The rotor form made of NACA 4412 profile, with two blades, which are coupled to the rotor with a twisting angle of 0° and a blade angle of 5° was defined as the rotor form yielding the highest performance. The energy which was generated by this rotor form was 161,73 mW.