Stability Of Blade Research Articles

Numerical Simulation Method for Fluid-Structure Interaction in Compressor Blades

A simulation method for fluid-structure interaction (FSI) in compressor blades was discussed to predict the aeroelastic stability of blades. Using the MFX, which is a Multi-Field Solver in ANSYS, the total force of computational fluid dynamics (CFD) have been interpolated to computational structural dynamics (CSD) grids, and then the vibration displacements of CSD nodes have been interpolated to CFD grids at the blade surface. In CFD analysis, the grid coordinates of the moveable region have been updated by multi-layer moving grid technique, and the finite volume method has been applied to calculate the Reynolds-averaged Navier-Stokes (RANS) equations closed by k-E turbulent model. For NASA Rotor 67, detect the displacement response of compressor blades at the design speed , and the aeroelastic stability of blades has been analyzed preliminarily. The study shows that the FSI procedure is feasible to predict the aeroelastic stability of compressor blades.

Study of Tensile Fracture Mechanisms of a Ni-base Superalloy Supercast 247A

The nickel base superalloy, supercast 247A gains its appropriate microstructure and high temperature strength through precipitation hardening mechanism. Because of their service conditions, tensile properties of the alloy have strong influence on stability and life of the turbine blades. Tensile fracture mechanisms of the cast and heat treated superalloy were studied in ambient temperature, with a constant strain rate of 0.1mm per minute. Scanning electron microscopy was used to provide structural and fractography evidence of the nickel base superalloy supercast 247A of different heat treatment conditions. The fractography results of the tensile tested specimens were in good agreement with the variation in alloy ductility. Many fractography features such as transgranular and intergranular fracture with fine dimples, cleaved facets and a combination of them were observed in the specimens tested at different heat treatment temperatures.

Mistuning and Structural Coupling Effects on Flutter of Turbomachinery Blades

A fast numerical method based on aeroelastic eigenvalue analysis is applied to study the effects of mistuning on the aeroelastic stability of turbomachinery blades in which the structural coupling is included by a simplified method and an influence coefficient method is employed to deal with the unsteady aerodynamic effects. Results show that there exists an optimal mistuning amount at which the system has the best aeroelastic stability. Structural coupling almost has no effects on aeroelastic stability of a tuned system. But the benefit of alternate frequency mistuning to aeroelastic stability is inhibited drastically when structural coupling is introduced into the bladed disk system.

Nonlinear aeroelastic stability analysis of wind turbine blade with bending–bending–twist coupling

In this study, the nonlinear aeroelastic stability of wind turbine blade with bending–bending–twist coupling has been investigated for composite thin-walled structure with pretwist angle. The aerodynamic model used here is the differential dynamic stall nonlinear ONERA model. The nonlinear aeroelastic equations are reduced to ordinary equations by Galerkin method, with the aerodynamic force decomposition by strip theory. The nonlinear resulting equations are solved by a time-marching approach, and are linearized by small perturbation about the equilibrium point. The nonlinear aeroelastic stability characteristics are investigated through eigenvalue analysis, nonlinear time domain response, and linearized time domain response.

Modeling of Abradable Coating Removal in Aircraft Engines Through Delay Differential Equations

In modern turbomachinery, abradable materials are implemented on casings to reduce operating tip clearances and mitigate direct unilateral contact occurrences between rotating and stationary components. However, both experimental and numerical investigations revealed that blade/abradable interactions may lead to blade failures. In order to comprehend the underlying mechanism, an accurate modeling of the abradable removal process is required. Time-marching strategies where the abradable removal is modeled through plasticity are available but another angle of attack is proposed in this work. It is assumed that the removal of abradable liners shares similarities with machine tool chatter encountered in manufacturing. Chatter is a self-excited vibration caused by the interaction between the machine and the workpiece through the cutting forces and the corresponding dynamics are efficiently captured by delay differential equations. These equations differ from ordinary differential equations in the sense that previous states of the system are involved in the formulation. This mathematical framework is employed here for the exploration of the blade stability during abradable removal. The proposed tool advantageously features a reduced computational cost and consistency with existing time-marching solution methods. Potentially dangerous interaction regimes are accurately predicted and instability lobes match both the flexural and torsional modal responses. Essentially, the regenerative nature of chatter in machining processes can also be attributed to abradable coating removal in turbomachinery.

The impact of yaw error on aeroelastic characteristics of a horizontal axis wind turbine blade

Horizontal axis wind turbines operate under yawed conditions for a considerable period of time due to the power control mechanism or sudden changes in the wind direction. This in turn can alter the dynamic characteristics of a turbine blade because the flow over the rotor plane may trigger complicated induced velocity patterns. In this study, an aeroelastic analysis under yawed flow conditions is carried out to investigate the effects of yaw error on the blade behaviors and dynamic stability. A beam model including geometric nonlinearity coupled with unsteady aerodynamics based on a free-vortex wake method with the blade element theory is employed in the present study. The aerodynamic approach for a horizontal axis wind turbine blade under yawed flow conditions is verified through comparison with measurements. It is also shown that the present method gives slightly better results at high yaw angles than does the method previously published in the literature. The dynamic instabilities of a National Renewable Energy Laboratory 5 MW reference wind turbine have subsequently been investigated for various wind speeds and yaw angles. Observations are made that yaw effects induce considerable changes in airloads and blade structural behavior. Also, the aeroelastic damping values for this particular blade under yawed flow conditions can be reduced by up to approximately 33% in the worst case. Therefore, it is concluded that the impacts of yaw misalignments adversely influenced the dynamic aeroelastic stability of the horizontal axis wind turbine blade.

Torsional Stiffness Effects on the Dynamic Stability of a Horizontal Axis Wind Turbine Blade

Aeroelastic instability problems have become an increasingly important issue due to the increased use of larger horizontal axis wind turbines. To maintain these large structures in a stable manner, the blade design process should include studies on the dynamic stability of the wind turbine blade. Therefore, fluid-structure interaction analyses of the large-scaled wind turbine blade were performed with a focus on dynamic stability in this study. A finite element method based on the large deflection beam theory is used for structural analysis considering the geometric nonlinearities. For the stability analysis, a proposed aerodynamic approach based on Greenberg’s extension of Theodorsen’s strip theory and blade element momentum method were employed in conjunction with a structural model. The present methods proved to be valid for estimations of the aerodynamic responses and blade behavior compared with numerical results obtained in the previous studies. Additionally, torsional stiffness effects on the dynamic stability of the wind turbine blade were investigated. It is demonstrated that the damping is considerably influenced by variations of the torsional stiffness. Also, in normal operating conditions, the destabilizing phenomena were observed to occur with low torsional stiffness.

Impact of the fuselage damping characteristics and the blade rigidity on the stability of helicopter

The aim of this work is to compare in the system of blade articulations, the hydraulic and elastomeric dampers in order to reduce the vibration level in the helicopter rotors. Based on an aerodynamic model, a three-dimensional model of the composite material blade was developed. Numerical calculations on the model developed taking into account the aeroelastic interaction prove that the elastomeric damper of viscoelastic type produces better results compared to other hydraulic damper. The study of the blade stability depending on the orientation of the composite fibers is an important factor to determine the rigidity of the structure.

Analysis of the influence of high-frequency current and annealing modes on the complex of mechanical properties of titanium alloy GTE compressor blades produced by high-speed stamping

The paper presents a pilot study and analysis of the influence of high-frequency current heating and annealing modes on the macro and microstructure, the complex of mechanical properties, the amount of buckling and thermal stability of blades produced by high-speed stamping. The possibility of straightening combined with thermal processing to obtain satisfactory geometry of blades without essential decrease in the complex of mechanical properties is investigated.

Limit vibration and pressure-pulsation cycles of the flow in the case of turbocharger rotor blade flutter

In this paper, the feasibility of limiting the flutter amplitudes of the axial turbocharger rotor blades by stabilizing the rotor speed is based on a study of experimentally confirmed required conditions. Two composite tasks are analyzed, the role of the contributions of structural damping and pressure pulsations in the air flow to the stability of the turbocharger blades’ vibrations and the parametric conditions for limiting the blade’s flutter amplitude at a stabilized rotor speed. It is shown that the blade’s flutter amplitude can be stabilized by increasing the quadratic damping of the acoustic diametral mode of the pressure pulsations in the air flow.

Stability analysis of a nonlinear rotating blade with torsional vibrations

This paper discusses the stability of a spinning blade having periodically time varying coefficients for both linear model and geometric nonlinear model. To obtain a reduced nonlinear model from nodal space, a standard modal reduction procedure based on matrix operation is developed with essential geometric stiffening nonlinearities retained in the equation of motion. For the linear model, the stability chart with various spinning parameters of the blade is studied via the Bolotin method, and an efficient boundary tracing algorithm is developed to trace the stability boundary of the linear model. For the geometric nonlinear model, the method of multiple time scale is employed to study the steady state solutions, and their stability and bifurcations for the periodically time-varying rotating blade. The backbone curves of steady-state motions are achieved, and the parameter map for stability and bifurcation is developed.

Multifunctional nanocomposite coating for wind turbine blades

In this study, multifunctional carbon nanofiber (CNF) paper-based nanocomposite coating was developed for wind turbine blades. The importance of vibration damping in relation to structural stability, dynamic response, position control, and durability of wind turbine blades cannot be underestimated. The vibration damping properties of the nanocomposite blades were significantly improved and the damping ratio of the nanocomposite increased by 300% compared to the baseline composite. In addition, the CNF paper-based composite exhibited good impact-friction resistance, with a wear rate as low as 1.78×10−4mm3/Nm. The nanocomposite also shows the potential to improve the blockage of water from entering the nanocomposite, being a superhydrophobic material, with a contact angle higher than 160.0°, which could improve the longevity of a wind turbine blade. Overall, multifunctional nanocomposite coating material shows great promise for usage with wind turbine blades, owing to its excellent damping properties, great friction resistance, and superhydrophobicity.

Numerical modeling of gas flow around oscillating compressor blades

The problem of gas flow around a plane cascade of oscillating blades is numerically solved using the ANSYS CFX package. The blade surface displacement is taken into account using a movable grid generated before the beginning of the calculations at each time step. The calculated and experimental data are compared. The calculated results are used for determining the blade stability against flutter.

Vibration and flutter of wind turbine blade modeled as anisotropic thin-walled closed-section beam

Based on a variational asymptotic analytical model, vibration and aeroelastic stability of rotor blades modeled as anisotropic thin-walled closed-section beams are systematically addressed. The analysis is applied to a laminated composite construction of the circumferentially asymmetric stiffness (CAS) that produces bending-twist coupling. The vibration characteristics of composite beam are determined by the Extended Galerkin Method. The unsteady aerodynamic loads and centrifugal force are integrated with the classical aerodynamic model to deal with aeroelastic stability analysis. The influence of some related factors, ply angle, rotating velocity, and wind speed, is investigated. The paper gives methods of eigenvalue analysis and aeroelastic response, and gives the approaches to restrain classical flutter.

Review of Dynamic Reliability Analysis on Wind Turbine

It’s significant to analyze the dynamic reliability of wind turbine in order to assure the safe and stable operation of wind turbine. In this paper, the dynamic reliability of wind turbine is analyzed with the propeller-type generator as example. The stability of blade of wind turbine under wind load is analyzed by calculating the fatigue load on blade. The frequencies of bending free vibration and torsion vibration of tower are summarized. Finally, the type of foundation and its simplified model are instructed and some useful conclusions are given for supplying basic information on dynamic performance of wind turbine.

Effect of steady deflections on the aeroelastic stability of a turbine blade

AbstractThis paper deals with effects of geometric non‐linearities on the aeroelastic stability of a steady‐state deflected blade. Today, wind turbine blades are long and slender structures that can have a considerable steady‐state deflection which affects the dynamic behaviour of the blade. The flapwise blade deflection causes the edgewise blade motion to couple to torsional blade motion and thereby to the aerodynamics through the angle of attack. The analysis shows that in the worst case for this particular blade, the edgewise damping can be decreased by half. Copyright © 2010 John Wiley & Sons, Ltd.

Vibration of Wind Turbine Blade Modeled as Composite Thin-Walled Closed-Section Structure

Based on a laminated composite structure, vibration and nonlinear stall aeroelastic stability of rotor blades modeled as anisotropic thin-walled closed-section beams are systematically addressed. The analysis is applied to a laminated construction of the circumferentially asymmetric stiffness (CAS) that produces bending-bending-twist coupling. The vibration characteristics of composite beam are determined by the Galerkin Method. The unsteady aerodynamic loads and centrifugal force are integrated with the nolinear aerodynamic model to deal with aeroelastic stability analysis. The influence of some related factors, pretwisted angle, ply-angle rotational speed, and wind speed, is investigated. The paper gives methods of eigenvalue analysis and aeroelastic response, which can determine the stability of the blade forced by the nolinear aerodynamics.

An anterior cervical retractor utilizing a novel principle

The alarmingly high soft-tissue complication rates after anterior cervical surgery suggests that the design of current retractors is inadequate. A review of retractor design and consideration of new designs is worthwhile. The author reviewed the literature and the 7 described devices (Cloward, Caspar, Thompson-Farley, Tresserras, Ozer, Takayasu, and Oh devices). With the exception of Cloward/Caspar and Thomson-Farley systems, the author's search of the literature failed to disclose any independent review or investigations of the other retractors, suggesting that the use of these devices is limited. The Cloward/Caspar-style retractors depend for stability on small teeth at the ends of the blades that impale and stretch the longus colli muscle. For stability this self-retaining design requires equal tissue counterpressure. These devices are thus ill suited for a wound with substantially greater pressure from the medial structures and are prone to migration. The Thomson-Farley type of systems use arms with mechanical joints fixed to a table-mounted frame. The releasable joints allow adjustability and independent relaxation. Their limitations include bulk causing obstruction to the surgeons and radiographs, increased setup time, and ease with which excessive force can be applied. The author describes a new anterior cervical retractor that is based on a novel principle. The principle is that bone fixation can be used to provide the retractor blade an axis of rotation inside the wound. This gives improved retractor blade stability with the mechanical advantage of a lever. The stable rotation produced allows adjustable retraction and tissue relaxation without compromise in stability. To the author's knowledge, there are no previously described retractors with this ability. The system consists of a small 2-piece sliding frame fixed to the spine with the distraction screws. Bone fixation is preferable to sharp teeth and longus colli dissection because it works better and heals without scarring. Surgery is carried out through the frame, which slides during distraction. Independent retractor blades are attached to the sides of the frame, which provides a stable craniocaudal axis inside the wound. The blades rotate to provide retraction or relaxation as required. Intermittent relaxation of tissues under retractors has been shown to be beneficial. Another advantage, compared with systems that maintain wounds with vertical sides, is the ease with which an oblique approach can be used. The mechanical advantage has 3 benefits. First, bulky external mechanisms for retraction are avoided, which improves access. Second, numerous blade lengths are unnecessary, reducing inventory. Third, radiolucent polymers can be used with "snap-fit" properties. The improved stability over conventional systems reduces the need for skilled assistance and avoids surgeon frustration after retraction migration. Over a 3-year period, 100 anterior cervical operations have been performed. Anecdotally, operations are quicker mainly because the retractors do not slip. Prospective clinical studies with independent evaluation are underway.

Formulation for flutter and vibration analysis of a hingeless helicopter blade in hover: part II. Results of flutter stability and vibration analysis of a hingeless helicopter blade in hover

PurposeThis study aims to carry out flutter stability and vibration analysis of a uniform hingeless rotor blade in hovering flight conditions.Design/methodology/approachThe perturbation equations are obtained using the governing differential equations of motion derived in Part I (Aircraft Engineering and Aerospace Technology, Vol. 79 No. 2, 2007). The differential transform method (DTM) is applied to the perturbation equations of motion and the transformed equations are coded in the computer package Mathematica.FindingsThe effects of the built‐in pretwist angle and the rotational speed ratio on the natural frequencies are investigated and the results are compared with the results in literature.Originality/valueThis study, in carrying out an analysis of flutter stability and vibration of a uniform hingless rotor blade, is in good agreement with previous studies in the literature.

Improvement of aeroelastic stability of hingeless helicopter rotor blade by passive piezoelectric damping

To augment weakly damped lag mode stability of a hingeless helicopter rotor blade in hover, piezoelectric shunt with a resistor and an inductor circuits for passive damping has been studied. A shunted piezoceramics bonded to a flexure of rotor blade converts mechanical strain energy to electrical charge energy which is dissipated through the resistor in the R-L series shunt circuit. Because the fundamental lag mode frequency of a soft-in-plane hingeless helicopter rotor blade is generally about 0.7/rev, the design frequency of the blade system with flexure sets to be so. Experimentally, the measured lag mode frequency is 0.7227/rev under the short circuit condition. Therefore the suppression mode of this passive damping vibration absorber is adjusted to 0.7227/rev. As a result of damping enhancement using passive control, the passive damper which consists of a piezoelectric material and shunt circuits has a stabilizing effect on inherently weakly damped lag mode of the rotor blades, at the optimum tuning and resistor condition.