Flexible Blades Research Articles

Self-Powered Sensing for Non-Full Pipe Fluidic Flow Based on Triboelectric Nanogenerators.

Fluidic flow monitoring of a non-full pipe is of great significance in the field of energy measurement and pipeline transportation. In this work, a monitoring method based on triboelectric nanogenerators for non-full pipe fluidic flow of large pipelines is proposed. Specifically, a triboelectric non-full pipe flow sensor (TNPFS) is fabricated, which can monitor the flow velocity and the liquid level simultaneously, and then the flow can be obtained by conversion. For flow velocity monitoring, the flexible blades slide between electrodes, generating periodic electrical signals. Interestingly, the frequencies of the voltage and flow velocities show a good linear relationship. For liquid level monitoring, according to the principle of liquid-solid contact electrification, a variable area interdigital electrode with a stable signal distributed on a polytetrafluoroethylene tube is designed. The experiments demonstrate that the peak number and trend of the voltage derivative curve are related to the liquid level. Finally, a real-time flow-monitoring system is established to effectively monitor the flow from 94 to 264 L/min. Compared with the actual measured flow, the error rate is under 1.95%. In addition to this, the TNPFS also has good responsiveness in sewage. This work provides a novel method for fluidic flow monitoring, especially the non-full pipe flow of large pipelines.

Land-based wind turbines with flexible rail-transportable blades – Part 1: Conceptual design and aeroservoelastic performance

Abstract. This work investigates the conceptual design and the aeroservoelastic performance of land-based wind turbines whose blades can be transported on rail via controlled bending. The turbines have a nameplate power of 5 MW and a rotor diameter of 206 m, and they aim to represent the next generation of land-based machines. Three upwind designs and two downwind designs are presented, combining different design goals together with conventional glass and pultruded carbon fiber laminates in the spar caps. One of the five blade designs is segmented and serves as a benchmark to the state of the art in industry. The results show that controlled flexing requires a reduction in the flapwise stiffness of the blades, but it represents a promising pathway for increasing the size of land-based wind turbine rotors. Given the required stiffness, the rotor can be designed either downwind with standard rotor preconing and nacelle uptilt angles or upwind with higher-than-usual angles. A downwind-specific controller is also presented, featuring a cut-out wind speed reduced to 19 m s−1 and a pitch-to-stall shutdown strategy to minimize blade tip deflections toward the tower. The flexible upwind and downwind rotor designs equipped with pultruded carbon fiber spar caps are found to generate the lowest levelized cost of energy, 2.9 % and 1.3 %, respectively, less than the segmented design. The paper concludes with several recommendations for future work in the area of large flexible wind turbine rotors.

Improvements on the Beddoes–Leishman dynamic stall model for low speed applications

Flexible wing and rotor blade designs operating at low Mach number (M≤0.3) environments may undergo or need to avoid stall flutter and, therefore, accurately predict dynamic stall airloads. At the preliminary stage, aeroelastic calculations routines place a limit on computational expenses and demand low-order models. However, the semi-empirical dynamic stall models used for such purposes still present some flaws for low freestream speeds, especially under stall onset and light stall conditions. Given that, the present paper proposes improvements for the Beddoes–Leishman model. Building upon past modifications for the low-speed dynamic stall, several modeling strategies for the onset of stall, reattachment, and vortex-shedding processes are introduced. These enhancements are extensively validated with previously available experimental data for the symmetric NACA 0012 and cambered AMES-01 airfoils, showing superior results over the base model for virtually all conditions tested, albeit requiring up to 40% longer computational time.

Turbulence structure and longitudinal velocity distribution of open channel flows with reedy emergent vegetation

AbstractThe vertical distribution of longitudinal velocity and the turbulence structure of open channel flows with natural‐like reedy emergent vegetation were investigated in this study. The natural‐like reedy vegetation consisted of a basal stem and flexible blades with shape and reconfiguration behaviour comparable with those found in actual riparian areas. The 3D velocity field was measured using an acoustic Doppler velocimeter. The vertically non‐uniform distribution of the frontal area could dramatically affect the exchange of mass and momentum between emergent vegetation and their surroundings. The average time velocity profile varied inversely with the frontal area. The high velocity gradient appearing at the middle section of the zone with frontal area varied considerably. The structures of vortices and vertical transport were analysed using spectral analysis and conditional sampling to identify the prominent vortical structures and their contribution to momentum transport. Spectral analysis suggested that the stem‐scale vortices set by stem spacing where the vertical frontal area had no clear change were dominant, and shear‐layer vortices where vertical frontal area dramatically changed cannot be disregarded. Quadrant analysis showed that inward and outward interactions were the dominant contributors to Reynolds stress, excluding the zones approaching the channel boundary and the vertical frontal area that dramatically changed. A four‐layer model was developed to predict the vertical distribution of longitudinal velocity with a newly established profile of local drag coefficient. The predicting results agreed well with the experimental data.

Internal, primary and combination resonances of a wind turbine blade with coupled flapwise and edgewise motions

In recent decades blades of wind turbines have been designed longer and longer for better performance of energy harvesting. The growth in structural flexibility has strengthened the effect of geometric nonlinearity and led to complicated nonlinear dynamic behavior of vibration response. In this paper, an investigation on internal, primary and multi-mode combination resonances of a flexible wind turbine blade with coupled flapwise and edgewise motions is studied. Through the Hamilton's principle, the dynamical model is established using the Euler-Bernoulli beam considering the actions of gravitational and unsteady aerodynamic force. The displacement of the blade is expanded into four basic modes based on the Galerkin's method, three in flapwise direction and one in edgewise direction. The governing equations of the four modal coordinates are solved using the method of multiple scales in transient and steady-state. For the transient responses, the internal and multi-mode combination resonances are revealed by the transfer of energy between resonant modes. Unlike the case of primary and internal resonances, the quasi-periodic under the multi-mode combination resonance is discovered through phase diagram of the first edgewise mode. For the steady-state responses, amplitude-frequency curves and phase diagrams of resonance modes under the primary and multi-mode combination resonance are derived. Influence of the combination resonance on the primary resonance is discussed for the steady-state responses with different aerodynamic force and geometric nonlinearity. Finally, parametric analyses are presented to show how steady-state motion of flapwise and edgewise modes vary with detuning parameters and design parameters.

The Effect of a Flexible Blade for Load Alleviation in Wind Turbines

This article presents the analysis of the performance of a flexible wind turbine blade. The simulation analysis is based on a 3 m span blade prototype. The blade has a flexible surface and a cam mechanism that modifies the aerodynamic profile and adapts the surface to different configurations. The blade surface was built with a flexible fiberglass composite, and the internal mechanism consists of a flexible structure actuated with an eccentric cam. The cam mechanism deforms five sections of the blade, and the airfoil geometry for each section was measured from zero cam displacement to full cam displacement. The measured data were interpolated to obtain the aerodynamic profiles of the five sections to model the flexible blade in the simulation process. The simulation analysis consisted of determining the different aerodynamic coefficients for different deformed surfaces and a range of wind speeds. The aerodynamic coefficients were calculated with the BEM method (QBlade®); as a result, the data performance of the flexible blade was compared for the different deformation configurations. Finally, a decrease of up to approximately 6% in the mean bending moment suggests that the flexible turbine rotor presented in this article can be used to reduce extreme and fatigue loads on wind turbines.

Blade Vibration and Its Effect on the Optimal Performance of Helicopter Rotors

In this paper, we develop a computationally efficient frequency-domain model that can be used to compute the required shaft power and vibratory loads for a trimmed helicopter rotor with flexible blades in forward flight. The aerodynamic forces and power are modeled using a vortex-lattice method. A finite element model based on the linearized form of the Hodges–Dowell rotating beam equations is used to model the vibrating blades. Guyan reduction and harmonic balance are used to reduce the number of degrees of freedom. The model is validated against several previous computational and experimental models, with generally good agreement. For rotors that use higher harmonic control, the problem of minimizing the required power and/or vibratory loads is cast as a quadratic programming problem requiring a single linear matrix solve to find the optimum. We show that for moderate and high advance ratios, higher harmonic control can substantially reduce vertical hub forces, but only with an increase in required cruise power. For example, using four-per-revolution higher harmonic control, the vertical vibratory loads on the four-bladed HART II rotor can be decreased by about 30% for a 3.0% increase in induced power for at a forward flight advance ratio of 0.45.

PIV and deformation measurements on the rotor blade of a rotating, scaled model wind turbine with flexible blades under tailored inflow conditions

Wind turbines face harsh inflow conditions when operating in the atmospheric boundary layer or in the wake of other wind turbines. The incoming velocity field can change within seconds due to the turbulent structures it contains, resulting in a rapid change of several degrees in the angle of attack for the rotating blade. Aerodynamics are hence rapidly altered, leading to changes of the occurring forces on the rotor. Such dynamic forces cause the blades to twist and bend, accelerating fatigue and reducing the lifetime of a turbine Spinato et al. (2009).

Ecological, physiological, and biomechanical differences between gametophytes and sporophytes of Chondrus ocellatus (Gigartinales, Rhodophyta)1.

Although variation among habitats in the ratio of gametophytes to sporophytes has been reported in various gigartinacean species, factors controlling the phase ratio remain poorly understood. Over 18months, we examined the phase ratio of Chondrus ocellatus at three sites: a sheltered intertidal site, Hiruga A; an exposed intertidal site, Hiruga B; and a subtidal site, Shikimi. The mean proportion of gametophytes at Hiruga A (73.1%) was significantly higher than that at Shikimi (51.2%) and Hiruga B (44.7%). Due to a significantly higher water retention ability of the gametophytes, it was expected that the gametophytes would exhibit higher desiccation tolerance. After dehydration treatments, however, neither the photosynthetic rate of vegetative blades nor the survival rate of spores was significantly different between the phases. Measurements of blade strength indicated that the sporophytic blades were less stiff and more flexible, and a culture experiment revealed that the sporophytic germlings showed a significantly higher growth rate. Flexible blades and fast-growing germlings are considered advantageous for colonizing wave-swept intertidal habitats, so these properties may have caused the different fluctuation pattern of phase ratio among the sites. The present data demonstrate that biomechanical and physiological differences between the two phases of C. ocellatus make one phase advantageous in certain environmental conditions, and that these differences likely cause an unequal ratio of isomorphic phases.

Влияние гидропневмоаккумулятора на гидропривод щеточного рабочего органа путевых машин легкого типа

The main direction of improving the repair processes of all types and the current maintenance of the track is to reduce the time and labor costs with the highest possible level of mechanization and automation of all types of track work. At the same time, a significant place is occupied by cleaning the tracks from weeds and excess ballast. The working body of the machines for performing these works is a brush picker with flexible blades, which provides cleaning of weeds and ballast below the level of the rail head. As a rule, on domestic machines, flexible blades are segments of a steel cable with a diameter of 16…21 mm. One of the main disadvantages of brush pickers with cable blades is the relatively low efficiency due to fatigue breaking of the flexible blades at the point of exit from the seal. There are also known design solutions with the use of blades made of rubber tape. The most successful is the combination of cable and belt blades on one picker. The main type of drive for such a working body should be considered a volumetric hydraulic drive, which allows you to solve the problem structurally in the simplest and most effective way. Since the picker blades interact with the object (ballast rubble) alternately ( usually there are 8-12 blades) the load on the drive is non-stationary, the pressure in the pressure line of the drive hydraulic motor changes sinusoidally, which negatively affects the reliability and durability of the drive. To smooth out pressure fluctuations, it is recommended to use a hydropneumulator.

Highly Flexible Wind Turbine Blades Utilizing Corrugated Surface Hinges

An anthropomorphic wind turbine blade was the suggested design that had a flexure hinge at root, middle, and tip regions. The inter-distances of the flexure hinges follow the Fibonacci sequence and resembled the natural finger through binding. Therefore, the present study designs various corrugated flexure hinges. NACA0012 is chosen as the basic airfoil for designing the corrugated flexure hinges with different geometrical profiles and leading edges. The designs are based on morphing technology and the main geometrical parameters of the corrugation, the pitch distance along the span and the height, are inspired by tubercles of the whale flippers. The study uses the finite element method to define the significant strength characteristics of each design flap-wise, edge-wise, torsional stiffness, and buckling resistance in order to assign the best fit corrugation profile for each region of the blade.

Layout optimization of auxiliary support for deflection errors suppression in end milling of flexible blade

The service performance and life of the aero-engine are directly affected by the blade machining accuracy. In the end milling of the flexible blade, the profile tolerance would usually be violated by the deflection errors induced by excessive static deformations under the action of milling force. In order to predict the blade deflection errors, this paper presents an iterative algorithm considering the coupling relationship between milling force and elastic deformation based on the milling finite element simulation model. Then a novel multipoint rod-shaped auxiliary support technology is proposed to suppress the blade deflection errors. Taking the influence of layout parameters on blade deflection errors into account, the layout of auxiliary support is optimized by a genetic algorithm. To verify the effectiveness of the proposed method, an auxiliary support mechanism is designed and manufactured, and the deflection errors suppression experiment is implemented. The measured results show that the prediction error of blade maximum deflection is 17.6%. Furthermore, the blade average deflection error on two measured curves reduces from 45.88 μm to 24.39 μm with the support of the designed mechanism. Thus, this auxiliary support mechanism and layout optimization method can achieve higher accuracy in blade milling.

Stability of helical vortex structures shed from flexible rotors

The presented investigation is motivated by the need to uncover connections between underlying rotor fluid–structure interactions and vortex dynamics to fatigue performance and characterization of flexible rotor blades, their hub, and their supporting superstructure. Towards this effort, temporal stability characteristics of tip vortices shed from flexible rotor blades are investigated numerically. An aeroelastic free-vortex wake method is employed to simulate the helical tip vortices and the associated velocity field. A linear eigenvalue stability analysis is employed to quantify stability trends (growth rate v. perturbation wavenumber) and growth-rate temporal evolution of tip vortices. Simulations of a canonical rotor with rigid blades and its generation of tip vortices are first conducted to validate the stability analysis employed herein. Next, a stationary wind turbine is emulated using the National Renewable Energy Laboratory (NREL) 5-MW reference wind turbine base design to investigate the impact rotor aeroelasticity has on tip-vortex stability evolution in time. Blade flexibility is shown to reduce the sensitivity of tip vortex destabilization to low wavenumber perturbations, also blade-pitch reduces growth-rate magnitude and alters the growth-rate peak dependence on perturbation wavenumber, all of which have in the past not been reported in the rotorcraft literature. The presented investigation aims to develop insight into the tip vortex kinematics and stability of the NREL 5-MW reference wind turbine. However, the frameworks presented herein can be applied to generalized rotor designs to work towards identifying the impact tip-vortex kinematics and stability have on fatigue loading and adverse blade–vortex interaction effects, such as excessive noise emission and rotor vibrations.

Wind turbines in atmospheric flow: fluid–structure interaction simulations with hybrid turbulence modeling

Abstract. In order to design future large wind turbines, knowledge is needed about the impact of aero-elasticity on the rotor loads and performance and about the physics of the atmospheric flow surrounding the turbines. The objective of the present work is to study both effects by means of high-fidelity rotor-resolved numerical simulations. In particular, unsteady computational fluid dynamics (CFD) simulations of a 2.3 MW wind turbine are conducted, this rotor being the largest design with relevant experimental data available to the authors. Turbulence is modeled with two different approaches. On one hand, a model using the well-established technique of improved delayed detached eddy simulation (IDDES) is employed. An additional set of simulations relies on a novel hybrid turbulence model, developed within the framework of the present work. It consists of a blend of a large-eddy simulation (LES) model by Deardorff for atmospheric flow and an IDDES model for the separated flow near the rotor geometry. In the same way, the assessment of the influence of the blade flexibility is performed by comparing two different sets of computations. The first group accounts for a structural multi-body dynamics (MBD) model of the blades. The MBD solver was coupled to the CFD solver during run time with a staggered fluid–structure interaction (FSI) scheme. The second set of simulations uses the original rotor geometry, without accounting for any structural deflection. The results of the present work show no significant difference between the IDDES and the hybrid turbulence model. In a similar manner, and due to the fact that the considered rotor was relatively stiff, the loading variation introduced by the blade flexibility was found to be negligible when compared to the influence of inflow turbulence. The simulation method validated here is considered highly relevant for future turbine designs, where the impact of blade elasticity will be significant and the detailed structure of the atmospheric inflow will be important.

A Quantitative Comparison of Aeroelastic Computations using Flex5 and Actuator Methods in LES

Actuator disc and actuator line techniques are widely used for modelling wind turbines operating in wind farms. These techniques essentially replace the blade geometry with applied body forces, which reduce the resolved length scales significantly and hence the required grid resolution. This work is a verification of the coupling between the flow solver EllipSys3D and the aeroelastic tool Flex5, through a quantitative comparison of coupled actuator line, coupled actuator disc, and standalone Flex5. Steady state performance predictions, instantaneous reaction to turbulence and damage equivalent load analyses all show a very good agreement between the three methods. Differences can be explained primarily by the higher fidelity modelling of the coupled simulations; this is particularly in regard to the influence of blade flexibility, as the actuators deflect and interact with the modelled flow. Additionally, some overpredictions of loading at the blade tip and root below rated velocity for the actuator methods can be attributed to the Gaussian smearing used to apply the body forces.

An improved theory in the determination of aerodynamic damping for a horizontal axis wind turbine (HAWT)

The aerodynamic damping reflects the aero-structure interaction and is intrinsically involved in a fully coupled turbine. However, it is still of great importance to theoretically quantify the aerodynamic damping of a HAWT in some cases. The existing theory can reasonably characterize the aerodynamic damping level of a HAWT with rigid blades, minute shaft tilt and yaw angles, while certain discrepancies were observed when compared with either experimental or numerical damping results of a more realistic turbine. This study aims to provide an improved theory to incorporate more realistic conditions (i.e., blade flexibility, shaft tilt and yaw angle) in aerodynamic damping estimation. Good agreements are found between the proposed theory and numerical results with varied influential factors, upon which modification factors against the original theory are created and discussed. Finally, the aerodynamic damping of tower is determined and included in a decoupled fatigue analysis framework to demonstrate the potential application of this improved aerodynamic damping theory.

Passive flow control mechanisms with bioinspired flexible blades in cross-flow tidal turbines

State-of-the-art technologies for wind and tidal energy exploitation focus mostly on axial turbines. However, cross-flow hydrokinetic tidal turbines possess interesting features, such as higher area-based power density in array installations and shallow water, as well as a generally simpler design. Up to now, the highly unsteady flow conditions and cyclic blade stall have hindered deployment at large scales because of the resulting low single-turbine efficiency and fatigue failure challenges. Concepts exist which overcome these drawbacks by actively controlling the flow, at the cost of increased mechatronical complexity. Here, we propose a bioinspired approach with hyperflexible turbine blades. The rotor naturally adapts to the flow through deformation, reducing flow separation and stall in a passive manner. This results in higher efficiency and increased turbine lifetime through decreased structural loads, without compromising on the simplicity of the design.Graphic abstract

Large eddy simulation of the fluid–structure interaction in an abstracted aquatic canopy consisting of flexible blades

Abstract

Investigating the aeroelasticity effects on aeroacoustics and aerodynamics of a MW-class HAWT

Abstract Employing large Horizontal Axis Wind Turbines, HAWTs, is inevitable for increasing the wind power generation per turbine unit, i.e. reducing the cost of wind energy production. The consequences of large HWATs application are considerable aeroelastic blade deformation and high levels of aeroacoustic noise generation. In this paper, considering the aeroelastic effects, aeroacoustic calculation of a MW class HAWT is performed by implementing a transient two-way partitioned Fluid-Solid Interaction (FSI) technique. The CFD-FEM and structural modeling are validated using AOC 50/15 HAWT experimental data. Aerodynamic and aeroacoustic simulations of WP_Baseline 1.5 ​MW HAWT are conducted. The results show the power amount and the noise level generated by the flexible blades are about 2.7% and 0.74 ​dB less than those generated by the rigid blades.

IoT BASED SMART AND EFFICIENT WIND TURBINE MONITORING SYSTEM

Wind Turbine industry has the improved latest generation of Wind turbines with bigger flexible blades, high tower, Good efficiency & low cost repairing in all platforms of wind turbines from Small wind mills to Ocean wind turbines. The Control centre is responsible for Monitoring and Controlling wind turbines in wind power farms. Various parameters like Oil level, Gas leakage, air pressure, vibrations & linear velocity, environmental condition like rain & humidity are to be monitored and controlled for proper working of the wind turbines. In the proposed work, smart and efficient turbine network architecture is designed to automate this process. The aim of the proposed work is to monitor the different parameters of the turbine using respective sensors. The acquired sensor data are uploaded to the cloud via WiFi module for online monitoring and further data analysis. IFTTT Server of Adafruit io cloud is used to send the warning notification of the critical sensor value to the concerned person. Also the sensor node life time is taken care by implementing a proposed compression algorithm in each node that reduces the amount of data transmitted and thereby the energy consumed during transmission.