Preliminary Analysis and Testing of the AWOG: A Novel Non-Rotational Wind Energy Extraction Device

2011 ◽  
Author(s):  
Jesse J. French ◽  
Colton T. Sheets
Keyword(s):  
Wind Tunnel ◽  
Wind Energy ◽  
Turbulent Flows ◽  
Power Output ◽  
Energy Extraction ◽  
Stored Energy ◽  
Practical Applications ◽  
Micro Scale ◽  
Aspect Ratios ◽  
Extraction Device

This paper highlights the work done by the authors to develop and test a novel, biologically inspired, non-rotational wind energy extraction device. This device capitalizes on the principles of a wind deflected shaft and vortex induced vibrations to generate micro-scale power. Piezoelectric and magnetic flux methods are explored as options to convert the stored energy of mechanical deflection to electrical power. The device is modeled after long-stemmed grasses, grains, and bamboos and geometrically mimics their aspect ratio in order to replicate their movement in low altitude, turbulent flows. This design is based on a significant sampling of the shaft aspect ratios and head shapes of naturally occurring biological samples collected in the field. This concept has been affectionately christened the AWOG (Amber Waves of Grain) and shows promise for use in highly turbulent, low-level air flows close to the ground or mounting surface. Potential operating sites of the AWOG, include locations very close to ground level, along building rooflines, and in urban settings. To determine the efficiency and power output of a single AWOG unit, wind tunnel testing and in-situ field testing were performed. Power stored in a single deflected AWOG has been experimentally determined to be 430 w/m^2, which is comparable to existing wind turbine designs. Initial tests outlined in this paper are only able to recover a fraction of the stored energy. Practical applications of AWOG units would be to use them in formation and examinations are included for several proposed grouping methods. Analysis is performed to determine the ideal arrangement for grouped AWOG units based on experimental and field data from biological specimens and wind tunnel tests. This includes analyzing the effect that different configurations have on individual power output and efficiency of the formation as a whole. Recommendations are made as to the feasibility of use in a variety of settings and consideration is given concerning scaling of the AWOG to the micro-scale and to larger scales.

scholarly journals Power Output Enhancement of a Ducted Wind Turbine by Stabilizing Vortices around the Duct

Energies ◽  
2019 ◽  
Vol 12 (16) ◽  
pp. 3171 ◽  
Author(s):  
Watanabe ◽  
Ohya ◽  
Uchida
Keyword(s):  
Wind Tunnel ◽  
Wind Energy ◽  
Numerical Simulations ◽  
Wind Turbine ◽  
Power Output ◽  
Vortex Structure ◽  
Energy Market ◽  
Energy Technology ◽  
Wind Tunnel Experiments ◽  
New Approaches

A brimmed-diffuser augmented turbine (called a wind lens turbine: WLT) actively uses vortices around the brim to enhance its power output. However, the vortices are usually unstable and asymmetric. This study attempted to stabilize the vortices to enhance the power output of a WLT. Then, we investigated new approaches using vortex stabilization plates and polygonal brims in wind tunnel experiments and numerical simulations. Both approaches achieved a 1.5–3.8% increase in power output compared with a standard WLT. Our numerical simulations revealed a periodicity existing in a fluctuating vortex structure on the circular brim. Importantly, vortex stabilization plates and polygonal brims must be the same periodic scale to suppress the vortex fluctuation and stabilize the vortices effectively. In addition, a larger brim tended to enhance the stabilizing effects. We believe that this discovery provides an easy way to increase the power output of existing wind turbines. It is particularly important in light of advances in wind energy technology and the increasing wind energy market.

A Numerical Study on the Performance Improvement for a Vertical-Axis Wind Turbine at Low Tip-Speed-Ratios

2017 ◽  
Author(s):  
Zhenyu Wang ◽  
Mei Zhuang
Keyword(s):  
Wind Speed ◽  
Wind Energy ◽  
Wind Turbines ◽  
Flow Separation ◽  
Power Output ◽  
Numerical Study ◽  
Leading Edge ◽  
Vertical Axis ◽  
Dynamic Stall ◽  
Energy Extraction

Vertical-axis wind turbines (VAWTs) are a promising solution for the use of renewable energy in residential areas. Compared to traditional horizontal-axis wind turbines (HAWTs), VAWTs are usually smaller, quieter, and insensitive to the wind direction and can be installed in a wide range of urban, suburban and rural places such as top of buildings, backyard, etc. In addition, VAWTs require a lower wind speed to self-start which increases the capability of wind energy extraction in the areas with low wind speed. However, VAWTs are less efficient and the power output of VAWTs is substantially affected by the phenomenon of dynamic stall induced by the variations of angle of attack of rotating blades, especially at low tip speed ratios (λTSR<4). When the dynamic stall vortices, formed near the leading-edge, are transported downstream, it creates large and sudden fluctuations in torques. At low values of the tip speed ratio and relatively low Reynolds number (Re<105), dynamic stall occurs periodically throughout the rotation of the blades. This results a sharp drop in lift coefficient and therefore rotor torque and power output are substantially reduced. The purpose of the present study is to investigate the prospects for improving the flow performances of small VAWTs using serrated leading-edge configurations on straight blades in a conventional H-type VAWT design to control dynamic flow separation. A numerical study is carried out to obtain the detailed flow fields for analysis and visualization. The results show that the turbine blade with the serration profiles of h = 0.025c (amplitude) and λs = 0.33c (wavelength) not only increased the power generation at low TSRs, but also enhanced the capability of wind energy extraction at the optimum TSR in comparison to the baseline model. The dynamic stall was suppressed significantly in the range of the azimuth angle from 80° to 160°. The flow separation induced by large angles of attack was essentially alleviated in the modified turbine model due to the serrated configuration implemented on the blade leading-edge.

Beating Betz: Energy Extraction Limits in a Constrained Flow Field

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Peter M. Jamieson
Keyword(s):  
Kinetic Energy ◽  
Flow Field ◽  
Wind Energy ◽  
Recent Analysis ◽  
Energy Extraction ◽  
Power Performance ◽  
Fluid Stream ◽  
Extraction Device ◽  
Ideal Limit ◽  
Constrained Flow

Experiments with diffusers and other flow concentrating devices have shown that the power performance coefficient Cp of an energy extraction device, defined in relation to the area of flow intercepted at the device, may exceed the Betz limit. “Beating Betz,” in that sense, has been long established but no theory has existed to define in a generalized way what ideal limit may apply to Cp in such situations. Recent analysis has resolved this. This indicates that, irrespective of the presence of flow concentration systems or other influences that perturb the flow but do not in themselves extract energy, there is a universal ideal limit of energy extraction. This is found to be 89 of the upstream kinetic energy in the streamtube associated with the energy extraction. Moreover, the familiar Betz equations for power and thrust coefficients can be generalized in a simple way to express this. Although this work has been developed in the context of wind energy, it will be apparent that the results are of general significance for any application of ducted rotors or propellers in a fluid stream.

The Effects of Turbulence Length Scale on the Performance of Piezoelectric Harvesters

2015 ◽  
Author(s):  
Yiannis Andreopoulos ◽  
Amir H. Danesh-Yazdi ◽  
Oleg Goushcha ◽  
Niell Elvin
Keyword(s):  
Turbulent Flows ◽  
Power Output ◽  
Isotropic Turbulence ◽  
Spatial Scales ◽  
Mechanical Energy ◽  
Relative Size ◽  
Analytical Description ◽  
Length Scale ◽  
Linear Effect ◽  
Turbulence Length

Turbulent flows carry mechanical energy distributed over a range of temporal and spatial scales and their interaction with a thin immersed piezoelectric beam results in a strain field which generates electrical charge. This energy harvesting method can be used for developing self-powered electronic devices such as flow sensors. In the present experimental work, various energy harvesters were placed in a turbulent boundary layer or inside a decaying flow field of homogeneous and isotropic turbulence. The role of large instantaneous turbulent structures in this rather complex fluid-structure interaction is discussed in interpreting the electrical output results. The forces acting on the vibrating beams have been measured dynamically and a theory has been developed which incorporates the effects of mean local velocity, turbulence intensity, the relative size of the beam’s length to the integral length scale of turbulence, the structural properties of the beam and the electrical properties of the active piezoelectric layer to provide reasonable estimates of the mean electrical power output. Experiments have been carried out in which these fluidic harvesters are immersed first in inhomogeneous turbulence like that encountered in boundary layers developing over solid walls and homogeneous and isotopic turbulence for which a simplified analytical description exists. It was found that there is a non-linear effect of turbulence length scales on the power output of the fluidic harvesters.

scholarly journals CFD Analysis of Urban Canopy Flows Employing the V2F Model: Impact of Different Aspect Ratios and Relative Heights

2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
Fabio Nardecchia ◽  
Annalisa Di Bernardino ◽  
Francesca Pagliaro ◽  
Paolo Monti ◽  
Giovanni Leuzzi ◽  
...  
Keyword(s):  
Flow Field ◽  
Water Channel ◽  
Flow Regimes ◽  
Two Dimensional ◽  
Mean Flow ◽  
Ansys Fluent ◽  
Practical Applications ◽  
Aspect Ratios ◽  
Starting Point ◽  
Step Down

Computational fluid dynamics (CFD) is currently used in the environmental field to simulate flow and dispersion of pollutants around buildings. However, the closure assumptions of the turbulence usually employed in CFD codes are not always physically based and adequate for all the flow regimes relating to practical applications. The starting point of this work is the performance assessment of the V2F (i.e., v2¯ − f) model implemented in Ansys Fluent for simulating the flow field in an idealized array of two-dimensional canyons. The V2F model has been used in the past to predict low-speed and wall-bounded flows, but it has never been used to simulate airflows in urban street canyons. The numerical results are validated against experimental data collected in the water channel and compared with other turbulence models incorporated in Ansys Fluent (i.e., variations of both k-ε and k-ω models and the Reynolds stress model). The results show that the V2F model provides the best prediction of the flow field for two flow regimes commonly found in urban canopies. The V2F model is also employed to quantify the air-exchange rate (ACH) for a series of two-dimensional building arrangements, such as step-up and step-down configurations, having different aspect ratios and relative heights of the buildings. The results show a clear dependence of the ACH on the latter two parameters and highlight the role played by the turbulence in the exchange of air mass, particularly important for the step-down configurations, when the ventilation associated with the mean flow is generally poor.

scholarly journals Three-dimensional stable lithium metal anode with nanoscale lithium islands embedded in ionically conductive solid matrix

2017 ◽  
Vol 114 (18) ◽  
pp. 4613-4618 ◽  
Author(s):  
Dingchang Lin ◽  
Jie Zhao ◽  
Jie Sun ◽  
Hongbin Yao ◽  
Yayuan Liu ◽  
...  
Keyword(s):  
High Power ◽  
Power Output ◽  
Three Dimensional ◽  
Rechargeable Batteries ◽  
Solid Matrix ◽  
Side Reactions ◽  
Surface Protection ◽  
Metal Anode ◽  
Practical Applications ◽  
Significant Step

Rechargeable batteries based on lithium (Li) metal chemistry are attractive for next-generation electrochemical energy storage. Nevertheless, excessive dendrite growth, infinite relative dimension change, severe side reactions, and limited power output severely impede their practical applications. Although exciting progress has been made to solve parts of the above issues, a versatile solution is still absent. Here, a Li-ion conductive framework was developed as a stable “host” and efficient surface protection to address the multifaceted problems, which is a significant step forward compared with previous host concepts. This was fulfilled by reacting overstoichiometry of Li with SiO. The as-formed LixSi–Li2O matrix would not only enable constant electrode-level volume, but also protect the embedded Li from direct exposure to electrolyte. Because uniform Li nucleation and deposition can be fulfilled owing to the high-density active Li domains, the as-obtained nanocomposite electrode exhibits low polarization, stable cycling, and high-power output (up to 10 mA/cm2) even in carbonate electrolytes. The Li–S prototype cells further exhibited highly improved capacity retention under high-power operation (∼600 mAh/g at 6.69 mA/cm2). The all-around improvement on electrochemical performance sheds light on the effectiveness of the design principle for developing safe and stable Li metal anodes.

scholarly journals Wind Tunnel testing of small Vertical-Axis Wind Turbines in Turbulent Flows

2017 ◽  
Vol 199 ◽  
pp. 3176-3181 ◽  
Author(s):  
Andreu Carbó Molina ◽  
Gianni Bartoli ◽  
Tim de Troyer
Keyword(s):  
Wind Tunnel ◽  
Turbulent Flows ◽  
Wind Turbines ◽  
Vertical Axis ◽  
Wind Tunnel Testing ◽  
Vertical Axis Wind Turbines ◽  
Tunnel Testing

Power Augmentation of a HAWT by Mie-type Tip Vanes, considering Wind Tunnel Flow Visualisation, Blade-Aspect Ratios and Reynolds Number

2003 ◽  
Vol 27 (3) ◽  
pp. 183-194 ◽  
Author(s):  
Yukimaru Shimizu ◽  
Edmond Ismaili ◽  
Yasunari Kamada ◽  
Takao Maeda
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Aspect Ratio ◽  
Reynolds Numbers ◽  
Flow Visualisation ◽  
Velocity Measurements ◽  
Horizontal Axis Wind Turbine ◽  
Aspect Ratios ◽  
Detailed Surface ◽  
Blade Tips

Wind tunnel results are reported concerning the effects of blade aspect ratio and Reynolds number on the performance of a horizontal axis wind turbine (HAWT) with Mie-type1 tip attachments. The flow behaviour around the blade tips and the Mie-type tip vanes is presented. Detailed surface oil film visualization and velocity measurements around the blade tips, with and without Mie vanes, were obtained with the two-dimensional, Laser-Doppler Velocimetry method. Experiments were performed with rotors having blades with different aspect ratio and operating at different Reynolds numbers. The properties of the vortices generated by the Mie vanes and the blade tips were carefully studied. It was found that increased power augmentation by Mie vanes is achieved with blades having smaller aspect ratio and smaller Reynolds number.

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