Blade Model Research Articles

Investigation of problems in modeling critical loads on a composite model of a wind turbine blade

This article deals with the problems of designing and analysis of the deformed state of the wind turbine blade under critical loads. A three-dimensional shell simulation model is built, taking into account the complex curvilinear geometry and the presence of reinforcing internal parts. The determination of the parameters of the stress-strain state under the influence of wind load was carried out on the basis of the finite element method. A shell ten-node isoparametric finite element was used. The constructed finite element model of the blade allows taking into account the composite structure and reproduced the presence of a different number of composite layers along the thickness of the shell, the diversity of fibers on individual layers, in particular, the curvilinear orthotropy of mechanical properties was modeled. The procedure of multi-layer structure setting is presented, which provides for superimposition of layers of composite one on the other in places of joint, which ensures compliance of model with technological peculiarities. Static analysis of structural deformation calculation is carried out taking into account lifting force and air head force. The strength analysis was performed for each of the layers according to the criterion of maximum deformations.
 Key words: composite material, wind turbine blade, strength, finite-elemental analysis, orthotropy of characteristics.

Determination of the response surface by strength and vibration parameters of the steam turbine blade

The work is devoted the definition of the function of limiting the geometric parameters of the steam turbine blade at given external loads. For this, a geometric model of a steam turbine blade was created, consisting of a blade body, a shank, and a shroud. The variable parameters were the angle of rotation of the middle section relative to the center of mass (which varied from 87 degrees to 92 degrees), as well as the length of the blade (varied from 495 mm to 525 mm). At the next stage, a finite element mesh was created. For the constructed model, an ordered finite element mesh was created in the area of the blade. Determined the stress-strain state of the blade during the operating mode. When carrying out the static analysis, an rotation velocity of 50 Hz was used as a load, and at the point of attachment of the disk in the shank, fixed displacement of all directions were used. The equivalent von Mises stresses and displacement in the structure are obtained. The zone of maximum stresses is located at the point where the blade is attached to the shank, but they do not exceed the limits. To determine the vibration characteristics of a steam turbine blade, its modal analysis was carried out taking into account the prestressed state from the action of static loads. The first six eigen modes of a steam turbine blade are obtained under the indicated initial conditions. The eigen frequency corresponding to the first form coincides with the rotational velocity (equal to 49 Hz), and the subsequent ones correspond to the multiplicities, respectively. At the next stage, a series of calculations was carried out to determine the response surface for the given parameters. The response surface for the maximum von Mises stresses and the first 4 modes of natural vibrations are determined. On the basis of the obtained results of studies of oscillations and deformed state of the blades with varying input parameters, it is possible to obtain a constraint for solving the optimization problem.

A comparison between aeroacoustic source mapping techniques for the characterisation of wind turbine blade models with microphone arrays

<p class="Abstract">Characterising the aeroacoustic noise sources generated by a rotating wind turbine blade provides useful information for tackling noise reduction of this mechanical system. In this context, microphone array measurements and acoustic source mapping techniques are powerful tools for the identification of aeroacoustic noise sources. This paper discusses a series of acoustic mapping strategies that can be exploited in this kind of applications. A single-blade rotor was tested in a semi-anechoic chamber using a circular microphone array. <br />The Virtual Rotating Array (VRA) approach, which transforms the signals acquired by the physical static array into signals of virtual microphones synchronously rotating with the blade, hence ensuring noise-source stationarity, was used to enable the use of frequency domain acoustic mapping techniques. A comparison among three different acoustic mapping methods is presented: Conventional Beamforming, CLEAN-SC and Covariance Matrix Fitting based on Iterative Re-weighted Least Squares and Bayesian approach. The latter demonstrated to provide the best results for the application and made it possible a detailed characterization of the noise sources generated by the rotating blade at different operating conditions.</p>

Horizontal Axis Wind Turbine Performance Analysis

The present work uses the method of Blade Element Momentum Theory as suggested by Hansen. The method applied to three blade models adopted from Rahgozar S. with the airfoil data used the data provided by Wood D. The wind turbine performance described in term of the thrust coefficient CT, torque coefficient CQand the power coefficient Cp. These three coefficient can be deduced from the Momentum theory or from the Blade element Theory(BET). The present work found the performance coefficient derived from the Momentum theory tent to over estimate. It is suggested to used the BET formulation in presenting these three coefficients. In overall the Blade Element Momentum Theory follows the step by step as described by Hansen work well for these three blade models. However a little adjustment on the blade data is needed. To the case of two bladed horizontal axis wind turbine, Hansen’s approach works well over if the blade radius is RBthe calculation should start from r = 0.1RB.

On the large-amplitude vibration of rotating pre-twisted graphene nanocomposite blades in a thermal environment

The large-amplitude free vibration behaviors of rotating pre-twisted functionally graded (FG) nanocomposite multilayered blade reinforced with graphene platelets (GPLs) in a thermal environment is comprehensively investigated in the paper. It is assumed that the GPLs volume fraction varies gradually from layer to layer across the blade thickness direction but remains constant in each individual GPLs-reinforced composite (GPLRC) layer. The modified Halpin-Tsai micromechanical model is exploited to obtain the effective Young’s modulus of each GPLRC layer while Poisson’s ratio, mass density, and thermal expansion coefficient are determined via Voigt’s rule. The nonlinear dynamic model of pre-twisted GPLRC blades at moderate rotational speed in a thermal environment is derived based on the first-order shear deformation theory (FSDT) combined with the improved version of the Novozhilov nonlinear shell theory. The nonlinear vibration characteristics of FG GPLRC blades are obtained by applying the element-free improved moving least-square Ritz (IMLS-Ritz) method in conjunction with a direct iterative scheme. Validation of obtained results is performed in detail and show effectiveness of used numerical approach and fast convergence of obtained results to exact values. The impacts of rotating speed, pre-twisted angle, presetting angle, and aspect ratio on nonlinear to linear frequency ratio of GPLRC blades are studied with emphasis on temperature rise and nano reinforcement parameters. Finally, new insights into dynamics of nanocomposite rotating blades with conclusions are presented in detail.

3D Printing of a miniature turbine blade model with an embedded fibre Bragg grating sensor for high-temperature monitoring

ABSTRACT Rapid advances in 3D printing enable the construction of complex metal structures. However, sensor embedding within 3D printed metal structures has been challenging due to its extremely high-temperature condition. Here, we embedded an optical fibre sensor for temperature monitoring within a Ni-alloy miniature turbine blade by directed energy deposition (DED) printing. To endure the high-temperature condition, a fibre Bragg grating (FBG) sensor was electroplated with a Ni layer, and various 3D printing parameters were optimised. In particular, to minimise the accumulation of thermal energy in the FBG sensor, ‘line-by-line printing and stop’ process was applied around the sensor. The embedded sensor accurately measured temperature cycling up to 500°C with the sensitivities of 28.3 and 27.2 pm/K in heating and cooling cycles, respectively. Finally, an FBG sensor was successfully embedded in a miniature turbine blade by our DED process, demonstrating its feasibility for high-temperature monitoring.

Composite materials in aircraft engine blades

The article investigates the strength of the propeller blades made of a multilayer composite material, subjected to centrifugal and gas loads with various combinations of fiberglass and carbon fiber and orientation of the material base. The finite element method is used as a research method. A propeller blade used in turbines of jet engines and compressors, made of composite materials, is considered as a naturally twisted rod, provided that the hypothesis of flat sections across the thickness of a multilayer composite package is valid under conditions of rigid contact at the boundary of layers. The propfan blade model is modeled by four-node finite elements of natural curvature with forty-eight degrees of freedom, taking into account the compression of the normal. The applied method for calculating the strength makes it possible to assess the strength of an arbitrarily reinforced blade in sections and layer by layer. The blades of hydrodynamic engines of the first and second stages were considered under the action of centrifugal and gas loads. The stress was determined at 17 points of 21 cross-sections in layers. As a result of the study, the strength parameters of the blades with different ratios of the dissimilar materials of the layers of the multilayer composite material were obtained. Conclusions are drawn, based on the fact that the blades made of composite material have significant advantages in terms of strength and weight characteristics compared to blades made of materials traditionally used in technology in the manufacture of propfans.

Main rotor blade modeling approaches comparison. Finite element and Craig-Bampton methods

The paper focuses on the helicopter main rotor blade FE model. And the main goal is to prove the feasibility of the helicopter main rotor MBD model in calculations of blade deformation as a result of applied aerodynamic forces. FE model is used as a basis for two different computational methods. A mathematical approach in the MBD based on the Craig-Bampton method on the one hand. And finite element model on the other hand. The results of high-frequency blade rotations are obtained. Calculations of these models are compared in order to determine the best method for modeling a linear-elastic blade. By the results, it is necessary to consider the preloaded state of the blade when using the Craig-Bampton method approach. The comparison of blade nodes displacements at various external conditions for both models are given. The influence of rotor MBS model damping parameters on the amplitude of blade oscillations under sinusoidal action is considered.

X-ray Computed Tomography Method for Macroscopic Structural Property Evaluation of Active Twist Composite Blades

This paper describes an evaluation of the structural properties of the next-generation active twist blade using X-ray computed tomography (CT) combined with digital image processing. This non-destructive testing technique avoids the costly demolition of the blade structure. The CT scan covers the whole blade region, including the root, transition, and tip regions, as well as the airfoil blade regions, in which there are spanwise variations in the interior structural layout due to the existence of heavy instrumentation. The three-dimensional digital image data are processed at selected radial stations, and finite element beam cross-section analyses are conducted to evaluate the structural properties of the blade at the macroscopic level. The fidelity of the digital blade model is first assessed by correlating the estimated blade mass with the measured data. A separate mechanical measurement is then carried out to determine the representative elastic properties of the blade and to verify the predicted results. The agreement is found to be good to excellent for the mass, elastic axis, flap bending, and torsional rigidity. The discrepancies are less than 2.0% for the mass and elastic axis locations, and about 8.1% for the blade stiffness properties, as compared with the measured data. Finally, a sensitivity analysis is conducted to clarify the impact of modeling the sensor and actuator cables, nose weight, and manufacturing imperfections on the structural properties of the blade.

АНАЛІЗ КОНСТРУКТИВНО-ТЕХНОЛОГІЧНИХ ОСОБЛИВОСТЕЙ ЛОПАТЕЙ НЕСУЧИХ ГВИНТІВ ВАЖКИХ ТРАНСПОРТНИХ ВЕРТОЛЬОТІВ

The analysis of the design and technological features of the rotor blades of heavy transport helicopters is carried out. The main performance characteristics of heavy helicopters are presented. General requirements to helicopter main rotor blades design and specifications for their production are formulated. The design and force diagram of heavy helicopter main rotor blades is considered. The features of structural materials for the main rotor blades of heavy transport helicopters are marked. The main rotor blades differ in their design due to different approaches to materials, manufacturing and layout of blade elements. The main rotor blades of an all-metal design, for design and technological reasons, are divided into two groups: a frame structure with a tubular steel spar and an aluminum extruded spar. As a result of a number of design and technological measures the service life of the main rotor blade of helicopter Mi-6 was brought from 50 hours to 1500 hours. The principal peculiarity of the steel tubular spar of the main rotor blade of the Mi-26 helicopter is the absence of the shaft lug. The features of mixed design main rotor blades are presented. The method of parametric modeling of helicopter main rotor blades is presented. The application of the three-dimensional parametric models of structural elements in practice of designing and construction enables to perform numerical calculations of aerodynamic and strength characteristics both of separate aggregates, units and details and of the helicopter as a whole by means of the finite element method. The method of parametric modeling of the main rotor blade of the transport helicopter with the computer system CATIA V5 is a modification of the method of integrated designing of the elements of aviation constructions. Parametric master geometry of the main rotor blade is a linear surface, created by basic profiles of the blade. On the basis of parametric master geometry a space distribution model is created that determines the position of axial planes of the power set of the blade for further creation of the blade detail models. Technological flowchart of main rotor blade manufacturing is presented, manufacturing and surface hardening technology of steel tubular spar is considered. The technology of manufacturing and molding the nose part of the blade of the main rotor mixed design. The technological features of slipway assembly-gluing of the main rotor blade are considered, the content of off-slipway work is given.These materials can be useful in theoretical and experimental studies to extend the service life of the rotor blades of Mi-26 helicopters, which are currently in operation in Ukraine.

Identification of the excitation source's circumferential position for rotating blades based on vibration phase

Wake excitation is the main cause of synchronous vibration of large rotating machines’ blades, whose circumferential position reflects the distortion position of flow field. However, little research has been published concerning the identification of excitation source's circumferential position based on blade vibration parameters. A new identification method using vibration phase is proposed in this paper. The excitation force model is established along with the forced vibration response model of blades under excitation sources. A phase unwrapping method is proposed to solve phase ambiguity, and the excitation source's circumferential position is achieved through vibration phase and engine orders of the same rotating blade in adjacent resonance regions. Experimental results verified the effectiveness and accuracy of the proposed method. The identification error of excitation source's circumferential position is less than ±1°.

Finite element analysis of wind turbine blades subjected to torsional loads: Shell vs solid elements

In this work the modelling of wind turbine blades subjected to torsional loads is explored. Usually, wind turbine blades are modelled using Outer Mold Layer (OML) shell models, whose mid-surface does not coincide with the nodal plane, and have been shown not to capture their behaviour correctly in torsional loadings, highly underestimating the torsional stiffness of the blade. To better understand the differences between using OML shell models and solid element models, a cylinder tube first is analysed and the conclusions from this study are applied for the wind turbine models. It was observed that artificial deformation modes were responsible for the erroneous results when using offset shell elements. These results can be drastically improved by controlling the stiffness associated with the drilling Degree Of Freedom (DOF). Furthermore, a high fidelity definition of the geometry of the blade is crucial to accurately capture its behaviour in torsion. By carefully controlling these parameters, the stiffness difference between the offset shell and solid models was reduced from 35% to 5%.

Finite Element Analysis of Tidal Turbine Blade Subjected to Impact Loads from Sea Animals

The present work investigates structural response of tidal stream turbine blades subjected to impact loads from sea animals. A full-scale tidal turbine blade model was developed using a finite element modelling software ABAQUS, while a simplified geometry of an adult killer whale (Orcinus orca) was assumed in simulating impact on the blade. The foil profiles along the turbine blade were based on the NACA 63-8XX series, while the geometric and material properties of the sea animal were calibrated with experimental results. The numerical model simulated the dynamic response of the blade, accounting for radial velocities of the blade corresponding to real life scenarios. Different magnitudes and trajectories of the velocity vector of the sea animal were simulated, in order to investigate their influence on the turbine blade’s plastic deformation. Furthermore, multiple impacts were analysed, in order to monitor the accumulation of plastic strain in the material of the blade. Finally, the potential application of stainless steel material in tidal stream turbine blades for impact resistance was evaluated, through comparison of numerical results obtained from models using stainless steel and mild carbon steel materials.

A computational model of the cereal leaves hydraulics

Environmental factors and plant architectonics significantly determine its water regime, namely, the water content and its movement through the tissues forced by the difference in water potentials, turgor pressure in cells, etc. In turn, the cumulative water regime affects the functioning and growth of cells, photosynthesis, and, as a result, the plant’s growth. The leaf contributes to the formation of the water regime and characterizes the contour of the plant’s adaptive system. Nevertheless, the data on the contribution of leaves to the total resistance to water transport in the plant and the structure of the hydraulic resistance of the leaf itself is still contradictory. This paper presents the formulation and justification of the monocots leaf hydraulics model based on Darcy’s law. The model was tested in computational experiments in the Comsol 4.3b package on idealized geometric models of leaf blades. Simulations showed the dependence of water potential distribution in xylem vessels and leaf mesophyll on the permeability of these tissues and on microclimatic parameters around the leaf. The adequacy of the model parameters selected as a result of testing is discussed.

Experimental Verification of the Elastic Response in a Numeric Model of a Composite Propeller Blade with Bend Twist Deformation.

Adaptive composite propeller blades showing bend twist behaviour have received increasing interest from hydrodynamic and structural engineers. When exposed to periodic loading conditions, such propellers can be designed to have higher energy efficiency and emit less noise and vibration than conventional propellers. This work describes a method to produce an adaptive composite propeller blade and how a point load experiment can verify the predicted elastic response in the blade. A 600 mm-long hollow full-size blade was built and statically tested in the laboratory. Finite element modelling predicted a pitch angle change under operational load variable loads of 0.55°, a geometric change that notably compensates for the load cases. In the laboratory experiment, the blade was loaded at two points with increasing magnitude. The elastic response was measured with digital image correlation and strain gauges. Model predictions and experimental measurements showed the same deformation patterns, and the twist angle agreed within 0.01 degrees, demonstrating that such propellers can be successfully built and modelled by finite element analysis.

Impact of the multi-claw combination on the soil-cutting performance of Scaptochirus moschatus (Mammalia, Soricomorpha, Talpidae)

Soil cutting is usually related to high energy consumption. Currently, much attention has been paid in optimizing the geometries of soil-engaging tools for improving cutting efficiency, however, with little research efforts concentrate on the aspect of the variation in soil failure characteristics for achieving a soil force reduction result. In this study, the effect of multi-claw combination of Scaptochirus moschatus (Mammalia, Soricomorpha, Talpidae) on draught force and soil failure characteristics was investigated in the soil bin. Three soil-cutting models, including a conventional model (C-model), a clawless blade model with a curved contour edge (BE-model) and a blade with multiple claws (BT-model), were designed according to the geometric characteristics of multi-claw combination and moved horizontally in soil. Draught force, its average value (\(\overline{F}\)) and fluctuation frequency (f), and soil rupture distance (r) of three models were measured and calculated at the rake angle from 10º to 90º. Results showed that the multi-claw combination had a great effect on the draught force and soil failure characteristics. The \(\overline{F}\), f, and r of BT-model were about 13.62% lower, 1.60 times higher, and 19.57% smaller than those of BE-model, respectively, which resulted in a smaller soil failure wedge to agree with the lower draught force of BT-model. And, the \(\overline{F}\) of BE-model were about 22.43% smaller than those of C-model; however, f, r, and soil failure wedge of BE-model were similar to those of C-model. It indicated that the curved contour edge of BE-model could not change the soil failure characteristics, whereas the multi-claw combination of BT-model could fundamentally change the soil failure characteristics, thus require a minimal force to cut soil. This study has unraveled the important roles of the multi-claw combination in determining the high soil-cutting efficiency of Scaptochirus moschatus, which will encourage the development of efficient soil-engaging tools potentially for engineering applications.

Colour changing material for the estimation of flue gas radiation on the miniature gas turbine surface

The gas turbine is being used in the applications of the aircraft propulsion system and land-based power generating systems more effectively. The manufacturers should optimise the temperature of the gas turbine engine components to enhance the life span of the components. The present research work concentrates on determining the surface temperature gradient on the fabricated turbine blades using a colour changing paint based on temperature attained on the surface. A calibration database has been created, and the surface temperature has been detected based on the available colour contours on the blade surface using human vision. An image processing algorithm has also been proposed for accurate temperature measurement on the blade surface. The obtained surface temperature using colour changing paint multi-colour change 350-8 has been calibrated with the conventional measurement technique IR thermography for experimental validation. A computational fluid dynamics simulation model of the turbine blade has been simulated to predict the surface temperature of blades using analysis systems fluid dynamics for numerical validation. The experimental and numerical validation results have shown a nominal value of error, which proves that the surface temperature gradient can be easily predicted with the help of temperature indicating paint using the proposed algorithm. The study has been extended further to evaluate the amount of emissive power radiated by the flue gas on the turbine blade surface based on the temperature and the wavelength of the colour obtained for the health monitoring of the blade.

A simulation framework for rotorcraft ice accretion and shedding

In this work a novel three-dimensional simulation framework for modelling the safety critical problem of rotorcraft ice formation and shedding is presented. To enable an entirely three-dimensional framework, state-of-the-art numerical modelling techniques are adopted and the inter-dependency between the techniques is discussed. The numerical techniques introduced in this work include models to simulate the rotor flow-field, water droplet trajectories and impingement locations, phase change modelling during the ice accretion, and mesh deformation to account for the moving ice boundary. A set of benchmark test cases are initially used for preliminary validation of the icing framework. This allows for a comparison of the collection efficiency and ice shapes with high-quality experimental measurements. Icing wind tunnel tests conducted on the Spinning Rotor Blade (SRB-II) model rotor are used for an assessment of the numerical predictions specific to rotorcraft. Quantities used for comparisons include the ice thickness and shedding location. Numerical predictions are in good agreement with the measured data at all temperatures. Additionally, the outcome of influential parameters which directly impact rotor ice shapes are assessed. In particular, the model for the temperature profiles within the ice layer, and the centrifugally induced movement of the liquid film.

PIV measurements over a double bladed Darrieus-type vertical axis wind turbine: A validation benchmark

Vertical axis wind turbines (VAWTs) are very attractive for in-home power generation since they can be adopted even at low wind speeds and highly variable wind direction. Even if significant experimental research activity has been carried out to improve VAWTs performance, the ability to accurately reproduce flow field characteristics around turbine blades by CFD (computational fluid dynamics) techniques represents a powerful approach to further enhance wind turbines performance. Thanks to CFD, in fact, it is possible to reproduce flow characteristics with a detail level impossible to achieve by experiments. Nevertheless, in order to appropriately analyze the flow structure by CFD application, an accurate validation is essential, and high-quality measurements of some main flow characteristics are required. In recent publications the authors investigated, both experimentally and numerically, the performance of an innovative double bladed Darrieus-type VAWT, with the aim to define an optimal configuration also focusing on self-starting ability of the prototype by employing CFD technique. Nevertheless, comparison between experiments and numerical results was made only in terms of power and torque coefficients. To overcome such limitation, in this paper the authors propose an experimental benchmark case for CFD results validation, describing detailed flow field in correspondence of one pair of blades of the innovative Darrieus-type VAWT in static conditions. Measurements were performed employing Particle Image Velocimetry (PIV) technique on a scaled model of the turbine blades realized by 3D printing. An uncertainty analysis was also performed which showed a high accuracy of the obtained experimental results. The measurements of the main flow characteristics (bi-dimensional velocity components) were then used for a test case CFD validation of two different turbulence models.

Prediction of flutter effects on transient flow structure and aeroelasticity of low-pressure turbine cascade using direct numerical simulations

The aerodynamic characteristics of advanced low-pressure turbines (LPTs) could be affected by the interaction between the transitional and turbulent flow and the dynamic behaviour of the blades. Consequently, analysing the details of the interactions between the transient flow, blade vibrations and the flutter occurrence over the blades of LPTs are essential in order to enhance the aerodynamic efficiency of the modern LPTs. The distinctive feature of the present analysis is performing high-fidelity simulations based on a DNS approach employing a 3D blade model to investigate the flutter instabilities in a T106A turbine at various inter blade phase angles (IBPAs) at different Reynolds numbers. The impacts of the flutter on the transient flow structure are examined by using a direct numerical simulation method. The results show that at IBPA=0∘, persistent patterns of vortex generation are detected with fluid flow mixing in the downward areas. For IBPA=180∘, however, the recirculation generated by the upper blades proceeds toward the lower ones and interferes with the shedding from the trailing edge which impact the wake structure in the downstream regions significantly. A three-dimensional frequency domain model based on the harmonic balance method is also proposed in this study to investigate the capabilities and limitations of frequency domain methods in predicting aeroelasticity and details of flow structures in LPTs.