Aerodynamic analysis of flapping-pitching flat plates

The roughness increase on horizontal axis wind turbine (HAWT) blade surface, especially on the leading edge, can lead to an aerodynamic performance degradation of blade and power output loss of HAWT, so roughness sensitivity is an important factor for the HAWT blade design. However, there is no criterion for evaluating roughness sensitivity of blade currently. In this paper, the performance influences of airfoil aerodynamic parameters were analyzed by the blade element momentum (BEM) method and 1.5 MW wind turbine blade. It showed that airfoil lift coefficient was the key parameter to the power output and axial thrust of HAWT. Moreover, the evaluation indicators of roughness sensitivity for the different spanwise airfoils of the pitch-regulated HAWT blade were proposed. Those respectively were the lift-to-drag ratio and lift coefficient without feedback system, the maximum lift-to-drag ratio and design lift coefficient with feedback system for the airfoils at outboard section of blade, and lift coefficient without feedback, maximum lift coefficient with feedback for the airfoils at other sections under the pitch-fixed and variable-speed operation. It is not necessary to consider the roughness when HWAT can be regulated to the rated power output by the pitch-regulated and invariable-speed operation.

<p>Flow control has significant technological importance as it can manipulate the flow field in a desired way either actively or passively. This wide research area has remained the point of attention for many years as it is applicable to various applications. Blowing as a flow control method, among other methods, is more technically feasible and market ready technique. A brief review from the existing literature on various studies on blowing has been presented along with their outcome. Then, studies were conducted to investigate the performance variation (in terms of lift coefficient, drag coefficient) of different airfoils with respect to various blowing parameters. It was observed that for NACA 0012 airfoil the maximum lift coefficient peaks at a blowing ratio 0.2 and then it decreases whereas the stalling angle increases with rise of blowing ratio. For LA203A both maximum lift coefficient and stalling angle increases with blowing ratio. For thick airfoil, it was found that lift increases with the rise of moment coefficient and blowing ratio and mid chord slots gives better performance at lower angles of attack whereas leading edge slots exhibits better performance at higher angles of attack. In case of thick elliptical airfoil, increase in lift coefficient was noticed with the increase in moment coefficient and blowing ratio but an optimum jet width to chord ratio (0.41) was found beyond which increase in jet width causes drop in lift coefficient. Additionally, it was found that at lower blowing angle thick elliptical airfoil performs better compared to that of higher angles of attack. Study on NACA 0012 and Aerospatiale A proved the fact that lifts increases with rise in blowing ratio at three different jet diameters to chord ratios. This study also found that higher blowing ratio is also advantageous for the turbo machinery in increasing the pressure difference. Lastly, the study on low Re airfoil flow found that increasing blowing ratio has a deleterious effect on aerodynamics performance (in terms of lift and drag coefficient).</p>

Influence analysis of rime icing on aerodynamic performance and output power of offshore floating wind turbine

In this study, we determined an aerodynamic configuration to design structures applying composites for large-scale horizontal-axis wind turbine blades. A new aerodynamic and structural design method for large wind turbine blades is presented. The rated power of the wind turbine blade is 25 MW class. The tip speed ratio is 7. The diameter of the designed blade is 260 m. Therefore, thick airfoils were selected to design large-scale wind turbine blades considering structural stiffness and maximum lift coefficients. For the aerodynamic design method, it was designed with the optimal angle of attack having the maximum lift-to-drag ratio. The blade element theory and vortex theory were applied to aerodynamic design. For the aerodynamic design results, its validity was investigated via aerodynamic performance analysis. As a result of analyzing aerodynamic performance, it was confirmed that higher power was generated. At 12.5 m/s of rated wind speed, electrical power was 28.32 MW. The structural design considering the aerodynamic design results was carried out. The composite laminate theory was adopted. Structural safety was evaluated for the designed blades. Finally, the structural design results were analyzed as sufficiently valid.

Design of 10 kW Horizontal-Axis Wind Turbine (HAWT) Blade and Aerodynamic Investigation Using Numerical Simulation

Making full use of wind energy can effectively alleviate the global energy shortage and environment contamination problems. Nevertheless, how to significantly improve the performance of the wind turbine airfoil and blade is a crucial issue. As the novel flow control method, the co-flow jet (CFJ) technology is one of the most potential methods to solve this problem. Thus, the effects of the CFJ technology on the performance enhancement of the S809 airfoil and Phase VI wind turbine blade are explored in this study. Furthermore, the effects of the injection location and jet momentum coefficient are studied, and an adaptive jet momentum coefficient strategy of the CFJ technology is proposed. Results demonstrate that the CFJ technology can significantly improve the maximum lift coefficient and maximum corrected lift-to-drag ratio of the S809 airfoil. Moreover, the power coefficient of the Phase VI wind turbine blade at the low tip speed ratio is greatly enhanced as well. In particular, the maximum lift coefficient and maximum corrected lift-to-drag ratio of the typical S809 CFJ airfoil with adaptive Cμ are improved by 119.7% and 36.2%, respectively. The maximum power coefficient of CFJ blade can be increased by 4.5%, and the power coefficient of CFJ blade can be boosted by 226.7% when the tip speed ratio is 1.52.

Hydrodynamic energy harvesting analysis of two piezoelectric tandem flags under influence of upstream body’s wakes

Increasing levels of modernization in different countries worldwide have lead to an exponential growth in national energy demand. India with its huge population base had a total grid connected electric power close to 285 GW during 2015 with annual generation of 1106 TWh accounting to a per-capita energy consumption of 746 kWh. The Government of India under its ambitious plan “Power for all” envisages 24 × 7 power supply for the entire domestic and Industrial loads by the year 2022. This power sector initiative also promises the generation through green path by targeting reduction in carbon footprint. The plan has sanctioned funds for production of 190 GW power based on go green initiative of United Nations Organization and a step forward to create a better environment for future generations. The proposed work aims at design of wind-solar hybrid system for light load decentralized applications. The computational tools were used to model and analyze wind turbine (WT) blade structure for low power applications to suit decentralized power generation based on renewable energy. The comparative studies of test aerofoil with standard NACA 0018 aerofoil indicated conformance of the test aerofoil as a profile for WT blades. The test aerofoil has the feature of easier manufacturability as against standard NACA 0018 profile adopted in commercial WT blades. The studies conformed suitability of test profile at specified angle of attack with WT blade structure and hub construction using balsa wood. The choice of balsa wood was based on properties of lighter weight and adequate strength that was supported on the designed tower of tripod type. The designed WT system was for a rated power output of 75 W while operating at an average wind speed of 4.5 m/s. The system developed will be a feasible option for powering households in rural India.

This paper studies the CFD simulation of forward three-dimensional (3-D) horizontal axis wind turbine (HAWT) blades. Using logarithmic grid and Q-criterion to learn the vortex dynamics around the blades at low rotational speed. The computational fluid dynamics (CFD) simulation uses Q-criterion to probe vortices and logarithmic grid to emphasize the micro-gridding effect of the turbulent boundary layer. The visualization & measurement of the simulation results give the coefficient of pressure (Cp). For forward 3-D wind turbine blade, at low rotational speed, the strongly accelerated laminar region surrounds the lower blade, and the decelerated tip blade region coalesce each other give rise to a reverse limiting streamline, eroding the laminar region further until a little is left on the tip of the blade. The "reverse limiting streamline" grows inward radially, the area is narrowing closing to the leading edge of the blade tip. The second side of the rolled-up vortex appears the velocity ratio (Uc/Ulocal) of the second vortices are higher than the main vortex cores. For radius R=1.547 m, U=12 m/s, at 210 RPM, CL and CD values reach a maximum with fully laminar tip conditions. While at 120 RPM, the CL and CD values reach a minimum in the absence of laminar tips. The results show the detailed vortex dynamic pattern surround the blades, give more understanding to design laminar 3-D blade toward a noiseless wind turbine system.

The major research work of the paper is the anomaly diagnosis of wind turbine generator based on voiceprint. The research finds that the reference and comparison between the three blades of a single wind turbine can diagnose whether the wind turbine is faulty. On this base, the paper proposes a periodic audio cutting method based on clustering and median convergence, which effectively cuts the voiceprint, reduces the amount of calculation, and provides a basis for subsequent anomaly detection. The steady-state difference method between three blades of wind turbine is used to detect anomalies, which avoids the migration failure of algorithm caused by the changes of channels and objects to be checked. The paper provides an effective technical means for fan blade inspection.

In this research, the flow physics and aerodynamic performance of dragonfly cross sections, used in Micro Aerial Vehicles (MAVs), in low Reynolds are investigated. The main objective of the research is to study the performance of dragonfly wing cross-sections flapping motion in Reynolds 5000 and 10,000. Pitching motion is one of the most important mechanisms in force lifting generation, and the effects of Reynolds number and mean angle of attack on aerodynamic coefficients have been extensively investigated for the pitching motion. In the present study, the geometry of two cross sections of dragonfly was extracted. Incompressible, two-dimensional and unsteady Navier–Stokes equations have been used to simulate the flow. k − ɛ RNG model was used for turbulence modeling. To simulate the wing pitching motion, the dynamic mesh method was used. The results showed that in flapping motion, pitching-up rotation has caused a rapid increase in lift coefficient. Furthermore, it was found that the absence of stall does not increase the lift and drag coefficients, while formation of new strong vorticity layers have caused an increase in lift coefficient. On the other hand, corrugations on the cross sections of the dragonfly in the pitching motion cause the delay of separation and increasing the lift coefficient. In flapping motion and the pitching motion, the lift coefficients of three cross sections were increased due to stronger vorticity layers by reducing the Reynolds number. Due to the existence of corrugations, the first and the second cross sections have good aerodynamic performance, compared to the flat plate. The comparison carried out in the current research showed that the second cross section is a proper replacement for the flat plate in MAVs.

Monitoring the blades of a wind turbine by using videogrammetry

Design optimization has been increasingly investigated for an airfoil, aiming to reduce the vorticity in the wake and increase the aerodynamic performance. In the current work, a two-dimensional (2D) S833 airfoil equipped with a flapping fringe at the trailing edge has been studied using computational fluid dynamics (CFD) simulations. The objective is to investigate the influence of the length (Lf) and flapping frequency (f) of the fringe on shedding vortices from the airfoil and the drag and lift coefficients. The validation of the current numerical approach for both static and dynamic motions of the airfoil was conducted. First, four different computational meshes were created for the static bare airfoil S833 model, and the simulated drag and lift coefficients were compared against experimental results. It is observed that the second finest mesh contributes to the best agreement with the measurement data. In addition, the numerical accuracy of the dynamic simulation was assessed by reproducing the pressure distribution around the airfoil NACA0014 with a periodic plunging motion at different time phases within one plunging cycle. Good agreements between the simulated and previous computational results are obtained. Moreover, the investigation of S833 airfoil equipped with a flapping fringe reveals that the model with Lf =0.01 m (10% of the chord length) associated with a flapping frequency below the shedding frequency of the bare airfoil can significantly alter the coherent structure of the shedding vortices, breaking the routine large-scale vortex into small-scale weak vortices. It also results in reducing the intensity of vortices and shortening the distance between each pair of vortices to accelerate the dissipation of vorticity. In addition, the equipped flapping trailing edge fringe can achieve extra benefit in aerodynamic performance in terms of the reduction of the drag coefficients and the enhancement of lift coefficients.

Live fish in nature exhibit various stiffness characteristics. The anguilliform swimmer, like eels, has a relatively flexible body, while the thunniform swimmer, like the swordfishes, has a much stiffer body. Correspondingly, in the design of biomimetic robotic fish, how to balance the non-uniform stiffness to achieve better propulsion performance is an essential question needed to be answered. In this paper, we conduct an experimental study on this question. First, a customized experimental platform is built, which eases the adjustment of the non-uniform stiffness ratio, the stiffness of the flexible part, the flapping frequency, and the flapping amplitude. Second, extensive experiments are carried out, finding that to maximize the propulsion performance of the biomimetic robotic fish, the non-uniform stiffness ratio is required to adapt to different locomotor parameters. Specifically, the non-uniform stiffness ratio needs to be reduced when the robotic fish works at low frequency, and it needs to be increased when the robotic fish works at high frequency. Finally, detailed discussions are given to further analyze the experimental results. Overall, this study can shed light on the design of a non-uniform biomimetic robotic fish, which helps to increase its propulsion performance.

Aeroelastic response and limit cycle oscillations for wing-flap-tab section with freeplay in tab