•Wind-induced vibrational energy can be harvested from the proposed system.•Energy harvesting process for impact-based DEG is validated experimentally.•Dynamical and electrical responses of the ...system subjected to wind are studied.•The system can work effectively within low wind speed ranges.•The distance between two membranes has influence on the system performance.
In this paper, a novel wind energy harvester is proposed and studied. The wind energy harvester consists of a conventional two-blade horizontal wind turbine and a vibro-impact (VI) dielectric elastomer generator (DEG) embedded symmetrically at the end of a rotating shaft. The wind energy is harvested by the VI DEG due to the rotational motion of the turbine's blades and the shaft. The dynamic model of the proposed system under wind-induced rotations is established theoretically, and the energy harvesting (EH) process of the VI DEG is introduced with the system output voltage and power being derived. The impact-based rotational energy harvesting process of the system is validated experimentally by measuring the output voltages of a single-sided impact (SSI) DEG under different impact velocities, and by measuring the ball's impact moments under rotational excitations, thus demonstrating the feasibility of the impact-based EH of DE material. Furthermore, the dynamical and electrical behaviors of the system under different wind speeds are fully studied through numerical simulations. The influences of the wind speed, tip speed ratio and the distance between dielectric elastomer membranes (DEMs) on the system EH performance are further discussed. It is found that the proposed wind energy harvester can work effectively in a range of small wind speed and produce a relatively high output power as large as 0.7125 mW under a wind speed of 3.99 ms−1. The tip speed ratio, distance between two DEMs can be selected as the adjusting parameter to produce optimal EH performance under different wind speeds, thus providing an effective solution for the design and improvement of the proposed system under different wind environments.
Abstract
Gas turbine play an important role in producing power for aviation industries. A sustainable operating life with high efficiency of a gas turbine requires very high temperature operation. ...The increase in thermal conductivity with temperature results in high thermal stress which leads to permanent deformation reducing blade life and efficiency. A thermal barrier coating is crucial to remove such detrimental effects. In the present work, an assessment of gas turbine blade materials has been carried out to study the effect of various coating techniques to improve longevity of blades. Coating methods have been found to play an important role in determining the sustainability of gas turbine performance. It was revealed that such coatings considerably reduce the heat penetration rate and thus increase the service life of gas turbine blades.
Summary
This study mainly focuses on improving the aerodynamic performance, analysing the turbulence effect and structural response of the horizontal axis wind turbine (HAWT) blade for energy ...production. The baseline blade geometry is modified using a winglet at the blade's tip to enhance aerodynamic efficiency. Adding a winglet to the blade tip improves the power performance by 4.2% to 25% at different wind speeds. This paper aims to investigate the turbulence effect on a HAWT blade without and with a winglet at the tip using numerical analysis. The results found that the overall performance of the wind turbine can be influenced depending upon the turbulence intensity. The torque generation is reduced by 11% and 8.54% for a baseline blade and blade with winglet, respectively, if turbulent intensity is increased by 10 times (from 3% to 30%). Furthermore, adding a winglet at the tip of the blade increases the weight of the wind turbine system and aeroelastic instability. The one‐way fluid‐structure interaction approach is used to study the aeroelastic effect. Three cases of varying tip speed ratios and two material properties are assessed for HAWT blades without and with winglet. Further, the results show that the total deformation and von Mises stress are within the permissible limits for both the materials studied.
This paper aims to investigate the turbulence effect on a horizontal axis wind turbine blade without and with a winglet at the tip using numerical analysis. The results found that The overall performance of the wind turbine can be influenced depending upon the turbulence intensity. Furthermore, adding a winglet at the tip of the blade increases the weight of the wind turbine system and aeroelastic instability.
Structural and parametric problems associated with physical parameterizations are often tied together in weather and climate models. This study examines the sensitivities of turbine‐height wind ...speeds to structural and parametric uncertainties associated with the planetary boundary layer (PBL) parameterizations in the Weather Research and Forecasting model over an area of complex terrain. The sensitivity analysis is based on experiments from two perturbed parameter ensembles using the Mellor‐Yamada‐Nakanishi‐Niino (MYNN) and Yonsei University (YSU) PBL schemes, respectively. In each scheme, most of the intermember variances can be explained by a few parameters. Compared to the YSU parameters, the MYNN parameters induce relatively weaker (stronger) impacts on wind speeds during daytime (nighttime). The two schemes can overall reproduce the observed diurnal features of turbine‐height wind speeds. Differences in the daytime wind speeds are evident between the two ensembles. The daytime biases exist even with well‐tuned parameter values in MYNN, indicating the structural error. The YSU scheme better matches monthly mean daytime observations, partly due to the compensation among the biases in different wind strengths. Compared to YSU, MYNN generally better agrees with observations in both weak and strong wind conditions. However, the improvements accomplished for one condition by parameter tuning may degrade model performances for others, suggesting the relationships that link different conditions are not accurately represented in the parameterizations. Simulated biases due to structural errors are further identified by evaluating them for different time of day and locations. Ultimately, this study improves understanding of structural limitations in the PBL schemes and provides insights on further parameterization development.
Key Points
MYNN parameters induce relatively weaker (stronger) impacts than YSU parameters on wind speeds during daytime (nighttime)
YSU scheme has a potential to better match daytime wind observations, while MYNN generally better matches the observations at night
Incompatible biases exist in different wind strengths, time of day, and locations due to structural inadequacy in both PBL schemes
•Dynamic stall of wind turbine airfoil with both VGs and LER is studied by URANS.•Increasing LER height further hinders the unsteady airfoil aerodynamic performance.•Serious LER may cause strong ...vortex shedding and change dynamic stall behaviors.•VGs can effectively control the dynamic stall and attenuate the adverse LER effect.•Double-row VGs generally perform better on roughened airfoils than single-row VGs.
Dynamic stall causes the highly unsteady and nonlinear aerodynamic loads on wind turbines. Recently, dynamic stall with passive vortex generators (VGs) and leading-edge roughness (LER) has received considerable attention, but independently. Therefore, this paper presents a careful investigation into dynamic stall of the NREL S809 airfoil with both VGs and LER to reveal their combined effect. Fully-resolved URANS simulations are conducted to identify the unsteady flow characteristics, and equivalent sand-grain roughness is used to model LER. LER significantly increases the turbulence kinetic energy (TKE) and suction loss at the leading edge, thereby causing the earlier onsets of separated flow and dynamic stall. Increasing roughness height generally reduces linear lift-curve slope, increases aerodynamic hysteresis and makes the separated flow hard to be reattached. VGs increase near-wall TKE via streamwise vortices and effectively suppress the separated flow. Dynamic stall is therefore significantly delayed by VGs with higher maximum lift, and aerodynamic hysteresis is also greatly reduced with the flow reattachment accelerated. Interestingly, serious LER may cause strong vortical disturbances and change the dynamic stall behaviors from light stall into deep stall. Double-row VGs are also found better than single-row VGs in improving the aerodynamic performance of roughened airfoil. These findings imply that VGs effectively control dynamic stall and diminish the adverse LER effect. This study should advance the control of unsteady loads on wind turbines suffering from harsh environmental conditions.
A wind turbine blade generally has complex structures including several layers of composite materials with shear webs, making its structure design very challenging. In this paper, a structural ...optimisation model for wind turbine composite blades has been developed based on a parametric FEA (finite element analysis) model and a GA (genetic algorithm) model. The optimisation model minimises the mass of composite blades with multi-criteria constraints. The number of unidirectional plies, the locations of the spar cap and the thicknesses of shear webs are taken as design variables. The optimisation model takes account of five constraints, i.e. stress constraint, deformation constraint, vibration constraint, buckling constraint, and manufacturing manoeuvrability and continuity of laminate layups constraint. The model has been applied to the blade structural optimisation of ELECTRA 30kW wind turbine, which is a novel VAWT (vertical-axis wind turbine) combining sails and V-shape arm. The mass of the optimised blade is 228kg, which is 17.4% lower than the initial design, indicating the blade mass can be significantly reduced by using the present optimisation model. It is demonstrated that the structural optimisation model presented in this paper is capable of effectively and accurately determining the optimal structural layups of composite blades.
Collisions, shear events and barotrauma are severe causes of fish mortality in a hydroelectric turbine. Fish-adapted turbine management and environmentally enhanced turbines can be mitigation ...measures. To use those measures efficiently, knowledge about turbine mortality is needed. In this study, a combination of CFD modelling, fish passage modelling and mortality assessment was used to evaluate mortality for different operating points of a Kaplan bulb turbine for adult European eels (anguilla anguilla). Calculated mortality due to collisions varied from 22% to 37%, due to shear events from 7% to 14% and due to barotrauma from 0% to 18%. The operating points with discharges between 70% and 85% of maximum discharge yielded the lowest mortality values. This supports the idea that a fish-adapted turbine management is possible that gives preference to operating points that are less hazardous to fish than others. Based on this approach it is possible to distinguish the locations within a turbine where hazardous hydraulic conditions occur making it a valuable tool in the design process and the biological performance evaluation of a turbine-management plan without needing to implement it first. Furthermore, no animal experiments are necessary for this approach.
•Collision yields the highest mortality risk for eels in a Kaplan turbine.•Barotrauma and shear events play a considerable part in turbine induced mortality.•Calculated mortality varied between turbine operating points.•Best operating points for fish passage coincide with peak efficiency points.
In the present study, the impact of utilizing an encompassing duct on the aerodynamic performance of a micro horizontal axis wind turbine (HAWT) was numerically and experimentally studied. A duct ...comprised of a diffuser and a flange was designed and constructed. A wind simulator facility and a micro scale wind turbine were employed to conduct the experimental investigations. Measurements of velocity and power output of the turbine have been carried out. The numerical results obtained at different stages of the research were validated separately and then compared with our experimental data and those obtained by other researchers. Consequently, the numerical predictions match well with the experimental measurements. In the first part of the study, fluid flow through the empty duct was analyzed. Then, by adding a nozzle at the diffuser entrance of the original duct, an improved design was proposed and numerically modeled to achieve higher wind speed at the throat position of the duct. The modified design was further enhanced by altering the converging and diverging section's angles (ranging from 0 to 90° with the angle increment step of 5°). Fifty-two different duct configurations have been considered to achieve the optimal angles of the nozzle, the diffuser, and the flange. Moreover, the aerodynamic performance of the micro HAWT was studied in three different conditions: without a duct, with the original duct, and with the improved duct. The results show that the improved duct increases the inlet wind speed from 5 m/s to 10.7 m/s (i.e., up to 2.14 times) at the throat position, which increases the wind speed up to 47% compared to the original duct. Furthermore, the power coefficient of the turbine increases from 0.33 to 1.2 (i.e., up to 3.64 times) in comparison to the case without duct, which increases by about 164% compared to the original duct. Also, employing the improved duct design causes a lower level of flow turbulence kinetic energy compared to the original duct design. This valuable outcome reduces the noise level generated by the system and the dynamics forced exerted by the rotor to other possible downstream structures.
•Three-dimensional numerical simulation of the flow around and within a nozzle-diffuser-flange duct with a wind turbine.•Experimental measurement of the aerodynamic performance of a micro HAWT mounted in the duct.•Improving the geometry of the duct to increase local wind speed and wind turbine power coefficient.•Achieving up to 3.64 time of power coefficient of the wind system using the improved duct.
Increasing concerns about environmental issues and depletion of fossil resources lead to a global need for producing more clean energy from renewable sources. For coastal areas or some remote ...islands, marine tidal current energy is a promising renewable power source due to its high predictability. During the last decades, prototypes of various horizontal and vertical axis marine current turbines (MCT) have been developed around the world. Although reviews on MCTs can be found in some state-of-the-art research papers in the last few years, many of the reported MCT projects were only at the planning/design stage when the papers were written. In fact, some projects do not have any further developments during the several years after their first reporting; and others have already upgraded their original designs and adopted up-scaled versions. In this paper, up-to-date information on large tidal turbine projects over 500kW is focused. The newest achievements of these large tidal current turbine technologies with their developing histories are presented. These technologies represent the industrial solutions for several pre-commercial MCT farm projects in the coming years. New developments in floating MCT technologies are also included. This paper provides a useful background for researchers in the tidal current energy domain and allows them to know the newest developments in large MCT projects around world.
Vision-based monitoring technology has been exploited for the surface damage detection of wind turbine blades (WTBs). However, the image quality is often significantly influenced by environmental ...illumination conditions, imposing difficulties for obtaining high detection accuracy for large-scale WTB surfaces. To improve the image quality and guarantee reliable damage detection on WTB surfaces, this study presents an image processing method for enhancing the images captured under non-uniform illumination conditions. First, cartoon and texture maps of the WTB images are constructed by cartoon texture decomposition. Second, an illumination model is established on the cartoon map from the Gaussian scale-space, to remove the non-uniform illumination. Third, the WTB images are enhanced by utilizing a multi-directional Gabor transformation to increase the contrast between the surface damage and image background. Finally, the WTB surface damages are detected using a gradient threshold segmentation method. The experimental results indicate that the damage detection accuracy of the WTB surfaces is significantly improved by using image enhancement. The F-measure and the intersection-over-union values of the damage detection are increased by 28.05% and 41.61%, respectively, relative to those detected from the input images. Therefore, this vision-based detection method for WTB surface damage inspection under non-uniform illumination has potential application values in practice.
•This work contributes to the wind turbine blade (WTB) surface damage detection under non-uniform illumination conditions.•The WTB images are decomposed to the cartoon and texture maps for enhancement processing.•The image contrast is increased based on the multi-directional Gabor transformation to improve the damage detection accuracy.•The proposed method can be developed for the product surface defect detection especially when the image samples are insufficient.
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