Journal articles: 'Blade flutter'

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Lobitz, Don W. "Parameter Sensitivities Affecting the Flutter Speed of a MW-Sized Blade." Journal of Solar Energy Engineering 127, no. 4 (July 12, 2005): 538–43. http://dx.doi.org/10.1115/1.2037091.

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With the current trend toward larger and larger horizontal axis wind turbines, classical flutter is becoming a more critical issue. Recent studies have indicated that for a single blade turning in still air the flutter speed for a modern 35 m blade occurs at approximately twice its operating speed (2 per rev), whereas for smaller blades (5–9 m), both modern and early designs, the flutter speeds are in the range of 3.5–6 per rev. Scaling studies demonstrate that the per rev flutter speed should not change with scale. Thus, design requirements that change with increasing blade size are producing the concurrent reduction in per rev flutter speeds. In comparison with an early small blade design (5 m blade), flutter computations indicate that the non rotating modes which combine to create the flutter mode change as the blade becomes larger (i.e., for the larger blade the second flapwise mode, as opposed to the first flapwise mode for the smaller blade, combines with the first torsional mode to produce the flutter mode). For the more modern smaller blade design (9 m blade), results show that the non rotating modes that couple are similar to those of the larger blade. For the wings of fixed-wing aircraft, it is common knowledge that judicious selection of certain design parameters can increase the airspeed associated with the onset of flutter. Two parameters, the chordwise location of the center of mass and the ratio of the flapwise natural frequency to the torsional natural frequency, are especially significant. In this paper studies are performed to determine the sensitivity of the per rev flutter speed to these parameters for a 35 m wind turbine blade. Additional studies are performed to determine which structural characteristics of the blade are most significant in explaining the previously mentioned per rev flutter speed differences. As a point of interest, flutter results are also reported for two recently designed 9 m twist/coupled blades.

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Li, Nailu, Mark J. Balas, Pourya Nikoueeyan, Hua Yang, and Jonathan W. Naughton. "Stall Flutter Control of a Smart Blade Section Undergoing Asymmetric Limit Oscillations." Shock and Vibration 2016 (2016): 1–14. http://dx.doi.org/10.1155/2016/5096128.

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Stall flutter is an aeroelastic phenomenon resulting in unwanted oscillatory loads on the blade, such as wind turbine blade, helicopter rotor blade, and other flexible wing blades. Although the stall flutter and related aeroelastic control have been studied theoretically and experimentally, microtab control of asymmetric limit cycle oscillations (LCOs) in stall flutter cases has not been generally investigated. This paper presents an aeroservoelastic model to study the microtab control of the blade section undergoing moderate stall flutter and deep stall flutter separately. The effects of different dynamic stall conditions and the consequent asymmetric LCOs for both stall cases are simulated and analyzed. Then, for the design of the stall flutter controller, the potential sensor signal for the stall flutter, the microtab control capability of the stall flutter, and the control algorithm for the stall flutter are studied. The improvement and the superiority of the proposed adaptive stall flutter controller are shown by comparison with a simple stall flutter controller.

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Sun, Da-Gang, Jin-Jun Guo, Yong Song, Bi-juan Yan, Zhan-Long Li, and Hong-Ning Zhang. "Flutter stability analysis of a perforated damping blade for large wind turbines." Journal of Sandwich Structures & Materials 21, no. 3 (April 28, 2017): 973–89. http://dx.doi.org/10.1177/1099636217705290.

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The flutter stability of wind turbine blades is one of the important contents in the research of wind turbines. The bending stiffness of blades has decreased with the development of large-sized wind turbines. To achieve damping flutter-suppressing on the long spanwise blades, perforated damping blade was proposed under the consideration of the structural damping factor and the structural stiffness in this paper. Through the study of the unit cell, the deformation model was established and the structural loss factor of the perforated damping blade was derived. The undamped blade and the perforated damping blade, combined with the relevant parameters of a 1500 kW wind turbine blade, were established to simulate the flutter-suppressing abilities and the structural stability. The dynamic response analysis was accomplished with the large deformation theory, and the MPC algorithm was used to realize grid mobile and data delivery, according to the Newmark time integration method. The comparison results show that the perforated damping blade has both a higher structural damping factor and a better structural stiffness.

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Wang, Hao, Jiao Jiao Ding, Bing Ma, and Shuai Bin Li. "The Time Domain Analysis of the Flutter of Wind Turbine Blade Combined with Eigenvalue Approach." Advanced Materials Research 860-863 (December 2013): 342–47. http://dx.doi.org/10.4028/www.scientific.net/amr.860-863.342.

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The aeroelasticity and the flutter of the wind turbine blade have been emphasized by related fields. The flutter of the wind turbine blade airfoil and its condition will be focused on. The eigenvalue method and the time domain analysis method will be used to solve the flutter of the wind turbine blade airfoil respectively. The flutter problem will be firstly solved using eigenvalue approach. The flutter region, where the flutter will occur and anti-flutter region, where the flutter will not occur, will be obtained directly by judging the sign of the real part of the characteristic roots of the blade system. Then the time domain analysis of flutter of wind turbine blade will be carried out through the use of the four-order Runge-Kutta numerical methods, the flutter region and the anti-flutter region will be gotten in another way. The time domain analysis can give the changing treads of the aeroelastic responses in great detail than those of the eigenvalue method. The flap displacement of wind turbine blade airfoil will change from convergence to divergence, and change from divergence to convergence extremely suddenly. During the flutter region, the flutter of wind turbine blade will occur extremely dramatically. The flutter region provided by the time domain analysis of the flutter of the blade airfoil accurately coincides with the results of eigenvalue approach, therefore the simulation results are reliable and credible.

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Saren, V. E. "Calculating blade ring flutter." Journal of Applied Mechanics and Technical Physics 38, no. 5 (September 1997): 728–34. http://dx.doi.org/10.1007/bf02467885.

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Gill, John D., Vincent R. Capece, and Ronald B. Fost. "Experimental Methods Applied in a Study of Stall Flutter in an Axial Flow Fan." Shock and Vibration 11, no. 5-6 (2004): 597–613. http://dx.doi.org/10.1155/2004/596706.

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Flutter testing is an integral part of aircraft gas turbine engine development. In typical flutter testing blade mounted sensors in the form of strain gages and casing mounted sensors in the form of light probes (NSMS) are used. Casing mounted sensors have the advantage of being non-intrusive and can detect the vibratory response of each rotating blade. Other types of casing mounted sensors can also be used to detect flutter of rotating blades. In this investigation casing mounted high frequency response pressure transducers are used to characterize the part-speed stall flutter response of a single stage unshrouded axial-flow fan. These dynamic pressure transducers are evenly spaced around the circumference at a constant axial location upstream of the fan blade leading edge plane. The pre-recorded experimental data at 70% corrected speed is analyzed for the case where the fan is back-pressured into the stall flutter zone. The experimental data is analyzed using two probe and multi-probe techniques. The analysis techniques for each method are presented. Results from these two analysis methods indicate that flutter occurred at a frequency of 411 Hz with a dominant nodal diameter of 2. The multi-probe analysis technique is a valuable method that can be used to investigate the initiation of flutter in turbomachines.

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Wang, Si-wen, Jing-long Han, Quan-long Chen, Hai-wei Yun, and Xiao-mao Chen. "New Method for Analyzing the Flutter Stability of Hingeless Blades with Advanced Geometric Configurations in Hovering." International Journal of Aerospace Engineering 2020 (February 17, 2020): 1–16. http://dx.doi.org/10.1155/2020/1891765.

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A new method used to analyze the aeroelastic stability of a helicopter hingeless blade in hovering has been developed, which is especially suitable for a blade with advanced geometric configuration. This method uses a modified doublet-lattice method (MDLM) and a 3-D finite element (FE) model for building the aeroelastic equation of a blade in hovering. Thereafter, the flutter solution of the equation is calculated by the V-g method, assuming blade motions to be small perturbations about the steady equilibrium deflection. The MDLM, which is suitable to calculate the unsteady aerodynamic force of nonplanar rotor blade in hovering, is developed from the doublet-lattice method (DLM). The structural analysis tool is the commercial software ANSYS. The comparisons of the obtained results against those in the literatures show the capabilities of the MDLM and the method of structural analysis. The flutter stabilities of swept tip blades with different aspect ratios are analyzed using the new method developed in this work and the usual method on the basis of the unsteady strip theory and beam model. It shows that considerable differences appear in the flutter rotational velocities with the decrease of the aspect ratio. The flutter rotational velocities obtained by the present method are evidently lower than those obtained by the usual method.

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8

Abdel-Rahim, A., F. Sisto, and S. Thangam. "Computational Study of Stall Flutter in Linear Cascades." Journal of Turbomachinery 115, no. 1 (January 1, 1993): 157–66. http://dx.doi.org/10.1115/1.2929200.

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Aeroelastic interaction in turbomachinery is of prime interest to opertors, designers, and aeroelasticans. Operation at off-design conditions may promote blade stall; eventually the stall pattern will propagate around the blade annulus. The unsteady periodic nature of propagating stall will force blade vibration and blade flutter may occur if the stall propagation frequency is entrained by the blade natural frequency. In this work a computational scheme based on the vortex method is used to simulate the flow over a linear cascade of airfoils. The viscous effect is confined to a thin layer, which determines the separation points on the airfoil surfaces. The preliminary structural model is a two-dimensional characteristic section with a single degree of freedom in either bending or torsion. A study of the relationship between the stall propagation frequency and the blade natural frequency has been conducted. The study shows that entrainment, or frequency synchronization, occurs, resulting in pure torsional flutter over a certain interval of reduced frequency. A severe blade torsional amplitude (of order 20 deg) has been computed in the entrainment region, reaching its largest value in the center of the interval. However, in practice, compressor blades will not sustain this vibration and blade failure may occur before reaching such a large amplitude. Outside the entrainment interval the stall propagation is shown to be independent of the blade natural frequency. In addition, computational results show that there is no entrainment in the pure bending mode. Rather, “de-entrainment” occurs with similar flow conditions and similar stall frequencies, resulting in blade buffeting in pure bending.

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9

Wang, Hao, Bing Ma, and Jiao Jiao Ding. "The Analysis of the Flutter Region of Wind Turbine Blade." Applied Mechanics and Materials 423-426 (September 2013): 1520–23. http://dx.doi.org/10.4028/www.scientific.net/amm.423-426.1520.

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As the wind turbine blade is becoming larger and larger, the flutter of the wind turbine blade has been paid great attention by many fields. The flutter region of the wind turbine blade airfoil was focused on. The equation of motion for the flutter of blade airfoil was established, based on the simplified aerodynamic force and torque. The flutter analysis of wind turbine blade was carried out with the four-order Runge-Kutta methods, and so the flutter region of the blade airfoil can be obtained. The results show that, there are two critical tip speed ratios for the given blade airfoil. When the tip speed ratio is below the low critical speed ratio, the blade airfoil is convergent. At the low tip speed ratio, the blade airfoil system will become divergent from convergent condition. When the tip speed ratio is between the low critical tip speed ratio and the high one, the blade airfoil system will diverge. At the high tip speed ratio, the system will become convergent from divergent condition. When the tip speed ratio is above the high critical tip speed ratio, the blade airfoil system will converge again. In addition, the torsional angular displacement and velocity always keep convergent, the flap velocity is slightly divergent, because they are not sensible to the change of the tip speed ratio, and they are difficult to cause flutter, so the torsional motion will be more stable than flap motion for the given blade airfoil. It can provide one of references for the determination of the blade airfoil.

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10

Kobayashi, H. "Annular Cascade Study of Low Back-Pressure Supersonic Fan Blade Flutter." Journal of Turbomachinery 112, no. 4 (October 1, 1990): 768–77. http://dx.doi.org/10.1115/1.2927720.

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Low back-pressure supersonic fan blade flutter in the torsional mode was examined using a controlled-oscillating annular cascade test facility. Precise data of unsteady aerodynamic forces generated by shock wave movement, due to blade oscillation, and the previously measured data of chordwise distributions of unsteady aerodynamic forces acting on an oscillating blade, were joined and, then, the nature of cascade flutter was evaluated. These unsteady aerodynamic forces were measured by direct and indirect pressure measuring methods. Our experiments covered a range of reduced frequencies based on a semichord from 0.0375 to 0.547, six interblade phase angles, and inlet flow velocities from subsonic to supersonic flow. The occurrence of unstalled cascade flutter in relation to reduced frequency, interblade phase angle, and inlet flow velocity was clarified, including the role of unsteady aerodynamic blade surface forces on flutter. Reduced frequency of the flutter boundary increased greatly when the blade suction surface flow became transonic flow. Interblade phase angles that caused flutter were in the range from 40 to 160 deg for flow fields ranging from high subsonic to supersonic. Shock wave movement due to blade oscillation generated markedly large unsteady aerodynamic forces which stimulated blade oscillation.

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11

OKAWA, Hirohisa. "Stall flutter of helicopter blade." Journal of the Japan Society for Aeronautical and Space Sciences 33, no. 377 (1985): 332–39. http://dx.doi.org/10.2322/jjsass1969.33.332.

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12

Hua, Xugang, Qingshen Meng, Bei Chen, and Zili Zhang. "Structural damping sensitivity affecting the flutter performance of a 10-MW offshore wind turbine." Advances in Structural Engineering 23, no. 14 (June 15, 2020): 3037–47. http://dx.doi.org/10.1177/1369433220927260.

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Classical flutter of wind turbine blades is one of the most destructive instability phenomena of wind turbines especially for several-MW-scale turbines. In the present work, flutter performance of the DTU 10-MW offshore wind turbine is investigated using a 907-degree-of-freedom aero-hydro-servo-elastic wind turbine model. This model involves the couplings between tower, blades and drivetrain vibrations. Furthermore, the three-dimensional aerodynamic effects on wind turbine blade tip have also been considered through the blade element momentum theory with Bak’s stall delay model and Shen’s tip loss correction model. Numerical simulations have been carried out using data calibrated to the referential DTU 10-MW offshore wind turbine. Comparison of the aeroelastic responses between the onshore and offshore wind turbines is made. Effect of structural damping on the flutter speed of this 10-MW offshore wind turbine is investigated. Results show that the damping in the torsional mode has predominant impact on the flutter limits in comparison with that in the bending mode. Furthermore, for shallow water offshore wind turbines, hydrodynamic loads have small effects on its aeroelastic response.

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13

Hsu, Chih-Neng. "A Study on Fluid Self-Excited Flutter and Forced Response of Turbomachinery Rotor Blade." Mathematical Problems in Engineering 2014 (2014): 1–20. http://dx.doi.org/10.1155/2014/437158.

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Complex mode and single mode approach analyses are individually developed to predict blade flutter and forced response. These analyses provide a system approach for predicting potential aeroelastic problems of blades. The flow field properties of a blade are analyzed as aero input and combined with a finite element model to calculate the unsteady aero damping of the blade surface. Forcing function generators, including inlet and distortions, are provided to calculate the forced response of turbomachinery blading. The structural dynamic characteristics are obtained based on the blade mode shape obtained by using the finite element model. These approaches can provide turbine engine manufacturers, cogenerators, gas turbine generators, microturbine generators, and engine manufacturers with an analysis system to remedy existing flutter and forced response methods. The findings of this study can be widely applied to fans, compressors, energy turbine power plants, electricity, and cost saving analyses.

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Kurkov, A. P., and O. Mehmed. "Optical Measurements of Unducted Fan Flutter." Journal of Turbomachinery 115, no. 1 (January 1, 1993): 189–96. http://dx.doi.org/10.1115/1.2929206.

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The paper describes a nonintrusive optical method for measuring flutter vibrations in unducted fan or propeller rotors and provides detailed spectral results for two flutter modes of a scaled unducted fan. The measurements were obtained in a high-speed wind tunnel. A single-rotor and a dual-rotor counterrotating configuration of the model were tested; however, only the forward rotor of the counterrotating configuration fluttered. Conventional strain gages were used to obtain flutter frequency; optical data provided complete phase results and an indication of the flutter mode shape through the ratio of the leading- to trailing-edge flutter amplitudes near the blade tip. In the transonic regime the flutter exhibited some features that are usually associated with nonlinear vibrations. Experimental mode shape and frequencies were compared with calculated values that included centrifugal effects.

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Sláma, Václav, Bartoloměj Rudas, Petr Eret, Volodymyr Tsymbalyuk, Jiří Ira, Aleš Macalka, Lorenzo Pinelli, Federico Vanti, Andrea Arnone, and Antonio Alfio Lo Balbo. "EXPERIMENTAL AND NUMERICAL STUDY OF CONTROLLED FLUTTER TESTING IN A LINEAR TURBINE BLADE CASCADE." Acta Polytechnica CTU Proceedings 20 (December 31, 2018): 98–107. http://dx.doi.org/10.14311/app.2018.20.0098.

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In this paper, experimental testing of flutter and numerical simulations using a commercial code ANSYS CFX and an in-house code TRAF are performed on an oscillating linear cascade of turbine blades installed in a subsonic test rig. Bending and torsional motions of the blades are investigated in a travelling wave mode approach. In each numerical approach, a rig geometry model with a different level of complexity is used. Good agreement between the numerical simulations and experiments is achieved using both approaches and benefits and drawbacks of each technique are commented in this paper. It is demonstrated that both used computational techniques are adequate to predict turbine blade flutter. It is concluded that validated numerical tools can provide a better insight of flutter phenomena of operationally flexible steam turbine last stage blades.

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Nowinski, M., and J. Panovsky. "Flutter Mechanisms in Low Pressure Turbine Blades." Journal of Engineering for Gas Turbines and Power 122, no. 1 (October 20, 1999): 82–88. http://dx.doi.org/10.1115/1.483179.

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The work described in this paper is part of a comprehensive research effort aimed at eliminating the occurrence of low pressure turbine blade flutter in aircraft engines. The results of fundamental unsteady aerodynamic experiments conducted in an annular cascade are studied in order to improve the overall understanding of the flutter mechanism and to identify the key flutter parameters. In addition to the standard traveling wave tests, several other unique experiments are described. The influence coefficient technique is experimentally verified for this class of blades. The beneficial stabilizing effect of mistuning is also directly demonstrated. Finally, the key design parameters for flutter in low pressure turbine blades are identified. In addition to the experimental effort, correlating analyses utilizing linearized Euler methods demonstrate that these computational techniques are adequate to predict turbine flutter. [S0742-4795(00)01301-6]

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Chang, Lin, Yingjie Yu, and Tingrui Liu. "Aeroelastic Flutter and Sliding Mode Control of Wind Turbine Blade." Shock and Vibration 2020 (July 26, 2020): 1–8. http://dx.doi.org/10.1155/2020/8846529.

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Flutter is an important form of wind turbine blade failure. Based on damping analysis, synthetically considering aeroelastic vibration instability of the blade and using the parameter fitting method, the aeroelastic flutter model of the pretwisted blade is built, with the simulation and emulation of flap and lead-lag directions flutter of the 2D dangerous cross section realized. Through the construction of two controllers, modular combinatorial sliding mode controller and sliding mode controller based on LMI for parameterized design suppress blade aeroelastic flutter. The results show that a better control effect can be achieved on the premise of the design of the precise parameters of the controller: the proposed sliding mode control algorithm based on LMI can effectively act on the aeroelastic system of the blade, significantly reduce the vibration frequency, and make the aeroelastic system converge to an acceptable static difference in a short time, which proves the effectiveness of sliding mode control in suppressing high-frequency vibration under high wind speed.

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Kobayashi, H. "Effects of Shock Waves on Aerodynamic Instability of Annular Cascade Oscillation in a Transonic Flow." Journal of Turbomachinery 111, no. 3 (July 1, 1989): 222–30. http://dx.doi.org/10.1115/1.3262259.

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The effects of shock waves on the aerodynamic instability of annular cascade oscillation were examined for rows of both turbine and compressor blades, using a controlled-oscillating annular cascade test facility and a method for accurately measuring time-variant pressures on blade surfaces. The nature of the effects and blade surface extent affected by shock waves were clarified over a wide range of Mach number, reduced frequency, and interblade phase angle. Significant unsteady aerodynamic forces were found generated by shock wave movement, which markedly affected the occurrence of compressor cascade flutter as well as turbine cascade flutter. For the turbine cascade, the interblade phase angle significantly controlled the effect of force, while for the compressor cascade the reduced frequency controlled it. The chordwise extent of blade surface affected by shock movement was estimated to be approximately 6 percent chord length.

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Kuroda, Hiromoto, Kiyoshi Nishioka, and Hitohiko Iwasaki. "Coupling Flutter of Circular Cascading Blade Rows with Splitter Blades." Transactions of the Japan Society of Mechanical Engineers Series B 61, no. 587 (1995): 2549–56. http://dx.doi.org/10.1299/kikaib.61.2549.

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Isomura, K., and M. B. Giles. "A Numerical Study of Flutter in a Transonic Fan." Journal of Turbomachinery 120, no. 3 (July 1, 1998): 500–507. http://dx.doi.org/10.1115/1.2841746.

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The bending mode Flutter of a modern transonic fan has been studied using a quasi-three-dimensional viscous unsteady CFD code. The type of flutter in this research is that of a highly loaded blade with a tip relative Mach number just above unity, commonly referred to as transonic stall flutter. This type of Flutter is often encountered in modern wide chord fans without a part span shroud. The CFD simulation uses an upwinding scheme with Roe’s third-order flux differencing, and Johnson and King’s turbulence model with the later modification due to Johnson and Coakley. A dynamic transition point model is developed using the en method and Schubauer and Klebanoff’s experimental data. The calculations of the flow in this fan reveal that the source of the flutter of IHI transonic fan is an oscillation of the passage shock, rather than a stall. As the blade loading increases, the passage shock moves forward. Just before the passage shock unstarts, the stability of the passage shock decreases, and a small blade vibration causes the shock to oscillate with a large amplitude between unstarted and started positions. The dominant component of the blade excitation force is due to the foot of the oscillating passage shock on the blade pressure surface.

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Fang, Li Cheng, and Shun Ming Li. "A Review of the Research on Aeroelasticity in Aero Turbomachinery." Advanced Materials Research 651 (January 2013): 694–700. http://dx.doi.org/10.4028/www.scientific.net/amr.651.694.

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Aeroelasticity in the form of blade flutter is a major concern for designers in the field of turbomachinery. This paper presents a review of the research and development on blade flutter modeling, including the unsteady aerodynamic model, the structural model and flutter prediction methods. Based on the presentation of these models, the fundamental mechanism and effects of different treatments are discussed. At the end of paper, some deficiencies in the research of flutter and difficulties in modeling fluid-solid coupling effects are pointed out, to which attention should be paid in future.

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Balakshin, O. B., and B. G. Kukharenko. "Spectral analysis of turbocompressor-blade flutter." Doklady Physics 52, no. 12 (December 2007): 670–73. http://dx.doi.org/10.1134/s1028335807120075.

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Pust, Ladislav, and Ludek Pesek. "Blades Forced Vibration Under Aero-Elastic Excitation Modeled by Van der Pol." International Journal of Bifurcation and Chaos 27, no. 11 (October 2017): 1750166. http://dx.doi.org/10.1142/s0218127417501668.

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This paper employs a new analytical approach to model the influence of aerodynamic excitation on the dynamics of a bladed cascade at the flutter state. The flutter is an aero-elastic phenomenon that is linked to the interaction of the flow and the traveling deformation wave in the cascade when only the damping of the cascade changes. As a case study the dynamic properties of the five-blade-bunch excited by the running harmonic external forces and aerodynamic self-excited forces are investigated. This blade-bunch is linked in the shroud by means of the viscous-elastic damping elements. The external running excitation depends on the ratio of stator and rotor blade numbers and corresponds to the real type of excitation in the steam turbine. The aerodynamic self-excited forces are modeled by two types of Van der Pol nonlinear models. The influence of the interaction of both types of self-excitation with the external running excitation is investigated on the response curves.

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Sinha, A., J. H. Griffin, and R. E. Kielb. "Influence of Friction Dampers on Torsional Blade Flutter." Journal of Engineering for Gas Turbines and Power 108, no. 2 (April 1, 1986): 313–18. http://dx.doi.org/10.1115/1.3239905.

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This paper deals with the stabilizing effects of dry friction on torsional blade flutter. A lumped parameter model with single degree of freedom per blade has been used to represent the rotor stage. The well-known cascade theories for incompressible and supersonic flows have been used to determine the allowable increase in fluid velocity relative to the blade. It has been found that the effectiveness of friction dampers in controlling flutter can be substantial.

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Sun, Tianrui, Anping Hou, Mingming Zhang, and Paul Petrie-Repar. "Influence of the Tip Clearance on the Aeroelastic Characteristics of a Last Stage Steam Turbine." Applied Sciences 9, no. 6 (March 22, 2019): 1213. http://dx.doi.org/10.3390/app9061213.

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In this paper, the tip clearance effects on the aeroelastic stability of a last-stage steam turbine model are investigated. Most of the unsteady aerodynamic work contributing to flutter of the long blades of the last-stage of a steam turbine is done near the tip of the blade. The flow in this region is transonic and sensitive to geometric parameters such as the tip clearance height. The KTH Steam Turbine Flutter Test Case was chosen as the test case, which is an open geometry with similar parameters to modern free-standing last-stage steam turbines. The energy method based on 3D URANS simulation was applied to investigate the flutter characteristics of the rotor blade with five tip gap height varying from 0–5% of the chord length. The numerical results show that the global aerodynamic damping for the least stable inter-blade phase angle (IBPA) increases with the tip gap height. Three physical mechanisms are found to cause this phenomenon. The primary cause of the variation in total aerodynamic damping is the interaction between tip clearance vortex and the trailing edge shock from the adjacent blade. Another mechanism is the acceleration of the flow near the aft side of the suction surface in the tip region due to the well-developed tip leakage vortex when the tip clearance height is greater than 2.5% of chord. This causes a stabilizing effect at the least stable IBPA. The third mechanism is the oscillation of the tip leakage vortex due to the blade vibration. This has a negative influence on the aeroelastic stability.

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Duquesne, Pierre, Quentin Rendu, Stephane Aubert, and Pascal Ferrand. "Choke flutter instability sources tracking with linearized calculations." International Journal of Numerical Methods for Heat & Fluid Flow 30, no. 9 (January 14, 2019): 4155–66. http://dx.doi.org/10.1108/hff-06-2018-0281.

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Purpose The choke flutter is a fluid-structure interaction that can lead to the failure of fan or compressor blade in turbojet engines. In ultra high bypass ratio (UHBR) fans, the choke flutter appears at part-speed regimes and at low or negative incidence when a strong shock-wave chokes the blade to blade channel. The purpose of this study is to locate the main excitation sources and improving the understanding of the different work exchange mechanisms. This work contributes to avoiding deficient and dangerous fan design. Design/methodology/approach In this paper, an UHBR fan is analyzed using a time-linearized Reynolds-averaged Navier–Stokes equation solver to investigate the choke flutter. The steady-state and the imposed vibration (inter blade phase angle, reduced frequency and mode shape) are selected to be in choke flutter situation. Superposition principle induced by the linearization allow to decompose the blade in numerous small subsections to track the contribution of each local vibration to the global damping. All simulations have been performed on a two-dimensional blade to blade extraction. Findings Result analysis points to a restricted number of excitation sources at the trailing edge which induce a large part of the work exchange in a limited region of the airfoil. Main phenomena suspected are the shock-wave motion and the shock-wave/boundary layer interaction. Originality/value An original excitation source tracking methodology allowed by the linearized calculation is addressed and applied to a UHBR fan test case.

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Huang, S. C., and K. B. Ho. "Coupled Shaft-Torsion and Blade-Bending Vibrations of a Rotating Shaft–Disk–Blade Unit." Journal of Engineering for Gas Turbines and Power 118, no. 1 (January 1, 1996): 100–106. http://dx.doi.org/10.1115/1.2816524.

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A new approach to analyzing the dynamic coupling between shaft torsion and blade bending of a rotating shaft–disk–blade unit is introduced. The approach allows the shaft to vibrate freely around its rotation axis instead of assuming a periodic perturbation of the shaft speed that may accommodate the shaft flexibility only to a limited extent. A weighted residual method is applied, and the receptances at the connections of blades and shaft–disk are formulated. Numerical examples are given for cases with between two and six symmetrically arranged blades. The results show not only coupling between the shaft, disk, and blades, but also coupling between individual blades where the shaft acts as a rigid support and experiences no torsional vibration. The blade-coupling modes occurred only in repeated frequencies. Finally, the effect of shaft speed on the modal frequencies was investigated. Plots illustrating the occurrence of critical speeds and flutter instabilities are presented.

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Zhu, Li Da, Wen Wen Liu, Ji Jiang Wu, Shuai Xu, and Peng Cheng Su. "Dynamic Characteristic Simulation and Analysis of Blade Flutter Based on Finite Element." Advanced Materials Research 753-755 (August 2013): 973–76. http://dx.doi.org/10.4028/www.scientific.net/amr.753-755.973.

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Blade is one of the main parts of aircraft engine. Its dynamic characteristics will produce important influence on the work efficiency and the operation reliability of the turbine engine. The paper used the theory of finite element to do modal simulation analysis on the dynamic characteristic of blade flutter, aiming at the phenomenon of serious blade vibration in the process of turbine engine running. Firstly, the paper generated a three-dimensional model by using the software UG. Then the three-dimensional model was leaded into the finite element analysis software ANSYS. Simulation analysis of the model was carried out by using the Workbench module of ANSYS software. Finally, we got the former six order natural frequencies and vibration modes of the blade. In addition, we got the blade's vibration characteristics. The results of the simulation could provide numerical basis for the blades optimization design and vibration safety inspection.

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29

Chiang, Hsiao-Wei D., and Sanford Fleeter. "Flutter control of incompressible flow turbomachine blade rows by splitter blades." Journal de Physique III 4, no. 4 (April 1994): 783–804. http://dx.doi.org/10.1051/jp3:1994162.

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30

Panovsky, J., and R. E. Kielb. "A Design Method to Prevent Low Pressure Turbine Blade Flutter." Journal of Engineering for Gas Turbines and Power 122, no. 1 (October 20, 1999): 89–98. http://dx.doi.org/10.1115/1.483180.

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A design approach to avoid flutter of low pressure turbine blades in aircraft engines is described. A linearized Euler analysis, previously validated using experimental data, is used for a series of parameter studies. The influence of mode shape and reduced frequency are investigated. Mode shape is identified as the most important contributor to determining the stability of a blade design. A new stability parameter is introduced to gain additional insight into the key contributors to flutter. This stability parameter is derived from the influence coefficient representation of the cascade, and includes only contributions from the reference blade and its immediate neighbors. This has the effect of retaining the most important contributions to aerodynamic damping while filtering out terms of less significance. This parameter is utilized to develop a stability map, which provides the critical reduced frequency as a function of torsion axis location. Rules for preliminary design and procedures for detailed design analysis are defined. [S0742-4795(00)01401-0]

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31

Kodama, H., and M. Namba. "Unsteady Lifting Surface Theory for a Rotating Cascade of Swept Blades." Journal of Turbomachinery 112, no. 3 (July 1, 1990): 411–17. http://dx.doi.org/10.1115/1.2927675.

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A lifting surface theory is developed to predict the unsteady three-dimensional aerodynamic characteristics for a rotating subsonic annular cascade of swept blades. A discrete element method is used to solve the integral equation for the unsteady blade loading. Numerical examples are presented to demonstrate effects of the sweep on the blade flutter and on the acoustic field generated by interaction of rotating blades with a convected sinusoidal gust. It is found that increasing the sweep results in decrease of the aerodynamic work on vibrating blades and also remarkable reduction of the modal acoustic power of lower radial orders for both forward and backward sweeps.

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32

Liu, Tingrui. "Stall Flutter Suppression for Absolutely Divergent Motions of Wind Turbine Blade Base on H-Infinity Mixed-Sensitivity Synthesis Method." Open Mechanical Engineering Journal 9, no. 1 (September 30, 2015): 752–60. http://dx.doi.org/10.2174/1874155x01509010752.

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This paper is devoted to solve the problem of stall flutter suppression for an absolutely divergent blade of small scale wind turbine. The blade is specially designed with absolutely divergent motions for the purpose of determining the most effective methods of active control for stall flutter suppression. A 2-DOF blade section is considered, with a simplified stall nonlinear aerodynamic model being applied. H-infinity mixed-sensitivity synthesis method with a new three-weight regulation is designed to control the time-domain instability of aeroelastic equations, with a third weight being chosen to weight complementary sensitivity for tracking problems and noise attenuation to robust stabilization in H-infinity control. Effects on flutter suppression are investigated based on different structural and external parameters. Apparent effects of H-infinity mixed-sensitivity method are displayed in the paper, when the other common intelligent control methods fail. The research provides a control way for absolutely divergent turbine blade motions.

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33

Kielb, R. E., and K. R. V. Kaza. "Flutter of Swept Fan Blades." Journal of Engineering for Gas Turbines and Power 107, no. 2 (April 1, 1985): 394–98. http://dx.doi.org/10.1115/1.3239739.

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The purpose of the research presented in this paper is to study the effect of sweep on fan blade flutter by applying the analytical methods developed for aeroelastic analysis of advanced turboprops. Two methods are used. The first method utilizes an approximate structural model in which the blade is represented by a swept, nonuniform beam. The second method utilizes a finite element technique to conduct modal flutter analysis. For both methods, the unsteady aerodynamic loads are calculated using two-dimensional cascade theories that are modified to account for sweep. An advanced fan stage is analyzed with 0, 15, and 30 deg of sweep. It is shown that sweep has a beneficial effect on predominantly torsional flutter and a detrimental effect on predominantly bending flutter. This detrimental effect is shown to be significantly destabilizing for 30 deg of sweep.

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34

Kielb, R. E. "Mass Balancing of Hollow Fan Blades." Journal of Engineering for Gas Turbines and Power 108, no. 4 (October 1, 1986): 577–82. http://dx.doi.org/10.1115/1.3239950.

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This paper uses a typical section model to investigate analytically the effect of mass balancing as applied to hollow, supersonic fan blades. A procedure to determine the best configuration of an internal balancing mass to provide flutter alleviation is developed. This procedure is applied to a typical supersonic shroudless fan blade which is unstable both in the solid configuration and when it is hollow with no balancing mass. The addition of an optimized balancing mass is shown to stabilize the blade at the design condition.

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35

Cai, Jin, Qing Ze Xu, and Zheng Wang. "Flutter Analysis of Compressor Blade Based on CFD/CSD." Applied Mechanics and Materials 50-51 (February 2011): 8–12. http://dx.doi.org/10.4028/www.scientific.net/amm.50-51.8.

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Based on the CFD/CSD (Computational Fluid Dynamics / Computational Structural Dynamics) algorithm, flutter characteristic and fluid structure interaction (FSI) problems of turbomachinery blades were studied in present paper. The three-dimensional unsteady Navier-Stokes equations and three-dimensional structural model were solved by the finite volume method and the finite element method, respectively. High accuracy in calculation and data exchange were gained by using load transfer, deformation tracking and synchronization between two solvers. The procedure successfully simulated the aeroelastic responses of a high performance fan rotor, NASA Rotor 67, over a range of operational conditions, and the results were compared with the experiment. The results show that the flutter mechanics of the compressor blade could be illustrated based on mean pressure and the distribution of cycle work, which is helpful for the decision of compressor stability.

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Vedeneev, Vasily V., Mikhail Kolotnikov, and Pavel Makarov. "Experimental Validation of Numerical Blade Flutter Prediction." Journal of Propulsion and Power 31, no. 5 (September 2015): 1281–91. http://dx.doi.org/10.2514/1.b35419.

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37

Namba, Masanobu, and Ryohei Nishino. "Flutter Analysis of Contra-Rotating Blade Rows." AIAA Journal 44, no. 11 (November 2006): 2612–20. http://dx.doi.org/10.2514/1.22561.

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38

Зиньковский, Анатолий Павлович, Анатолий Леонидович Стельмах, and Сергей Николаевич Кабанник. "РЕЗУЛЬТАТЫ ОЦЕНКИ ДИНАМИЧЕСКОЙ УСТОЙЧИВОСТИ К ДОЗВУКОВОМУ ФЛАТТЕРУ ЛОПАТОЧНЫХ ВЕНЦОВ КОМПРЕССОРОВ НЕКОТОРЫХ АВИАЦИОННЫХ ГАЗОТУРБИННЫХ ДВИГАТЕЛЕЙ." Aerospace technic and technology, no. 8 (August 31, 2019): 78–84. http://dx.doi.org/10.32620/aktt.2019.8.12.

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The paper outlines the results of the investigation on the verification of the express method of prediction of dynamic stability for subsonic flutter using the blade assemblies of individual stages of the compressor of some types of aircraft gas-turbine engines at different modes of their operation. The paper gives a brief overview of the basic concepts of the developed express estimation method, possibilities of the determination of the stability limit for the blade assemblies for a subsonic flutter, as well as the results of the assessment of the dynamic stability of the compressor stages of some modern aircraft gas-turbine engines. Firstly, the reduced frequencies of vibrations of the blade assemblies under investigation and their critical values coincide practically. The mentioned critical values were determined from the test data for the straight cascades of the blade airfoils corresponding to two sections of the height of the blade airfoil portion. Hence it follows that the task can be solved employing only gas-dynamic parameters of the flow for one of the sections of the airfoil within the specified range of its height. Secondly, the prediction of dynamic stability for the subsonic flutter of the blade assemblies of separate compressor stages of some types of aircraft gas-turbine engines and the comparison of the obtained results with the data of bench tests, as well as the data obtained using other methods, were made. It was implied that the developed method allows one to determine the flutter limit with high accuracy, as well as make an optimal selection of the values of the reduced frequency of the blade vibrations for the specified range of the angle of attack of the sections of the blade assemblies upon the condition of its occurrence. Thirdly, the possibility to determine the nature of vibration excitation for the blade assemblies is considered using the analysis of the initiation of cracks in the blade root of the first compressor stage of the high-pressure gas-turbine engine. Moreover, it is shown that at large angles of attack (≥ 10°) an insignificant displacement of the dynamic stability limit of the blade assemblies may occur in the direction of large values of the reduced frequency of their vibrations.

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39

Liu, Tingrui. "Classical Flutter and Active Control of Wind Turbine Blade Based on Piezoelectric Actuation." Shock and Vibration 2015 (2015): 1–13. http://dx.doi.org/10.1155/2015/292368.

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The aim of this article is to analyze classical flutter and active control of single-cell thin-walled composite wind turbine blade beam based on piezoelectric actuation. Effects of piezoelectric actuation for classical flutter suppression on wind turbine blade beam subjected to combined transverse shear deformation, warping restraint effect, and secondary warping are investigated. The extended Hamilton’s principle is used to set up the equations of motion, and the Galerkin method is applied to reduce the aeroelastic coupled equations into a state-space form. Active control is developed to enhance the vibrational behavior and dynamic response to classical aerodynamic excitation and stabilize structures that might be damaged in the absence of control. Active optimal control scheme based on linear quadratic Gaussian (LQG) controller is implemented. The research provides a way for rare study of classical flutter suppression and active control of wind turbine blade based on piezoelectric actuation.

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40

Tripp, Nicolás G., Aníbal E. Mirasso, and Sergio Preidikman. "Numerical analysis of the influence of inertial loading over morphing trailing edge devices." Journal of Intelligent Material Systems and Structures 29, no. 18 (June 28, 2018): 3533–49. http://dx.doi.org/10.1177/1045389x18783867.

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Larger and more flexible wind turbine blades are currently being manufactured. Those highly flexible blades suffer from loading of aeroelastic nature which increases the fatigue damage. Smart blade concepts are being developed to reduce the aerodynamic loading. The state of the art favors the discrete deformable trailing edge concept. Many authors have reported adequate performance of this type of actuators in reducing the blade vibrations. However, the question of whether the actuator can maintain its authority under strong external loading remains still answered. To solve this question, actuator models that include the loading produced by the blade vibration are required. In this article, a smart morphing trailing edge model is presented that includes the inertial forces produced by the blade dynamics. The model is applied to a commercial actuator and the influence of its parameters is analyzed. Finally, a simple estimation of the inertial loading produced by a 35-m wind turbine blade at the flutter instability condition is analyzed to understand the design requirements of this type of systems.

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41

Singh, Beerinder, and Inderjit Chopra. "Elastic-Blade Whirl Flutter Stability Analysis of Two-Bladed Proprotor/Pylon Systems." Journal of Aircraft 42, no. 2 (March 2005): 519–27. http://dx.doi.org/10.2514/1.2814.

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42

Liu, Zhanhe, Jinlou Quan, Jingyuan Yang, Dan Su, and Weiwei Zhang. "A High Efficient Fluid-Structure Interaction Method for Flutter Analysis of Mistuned." Xibei Gongye Daxue Xuebao/Journal of Northwestern Polytechnical University 36, no. 5 (October 2018): 856–64. http://dx.doi.org/10.1051/jnwpu/20183650856.

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The time cost is very high by direct fluid-structure interaction method for mistuned bladed disk structures, so aerodynamic loads generally are ignored or treated as small perturbations in traditional flutter analysis. In order to analyze the flutter characteristics of mistuned blade rapidly and accurately, this paper presents an efficient fluid-structure interaction method based on aerodynamic reduced order model. system identification technology and two basic assumptions are used to build the unsteady aerodynamic reduced order model. Coupled the structural equations and the aerodynamic model in the state space, the flutter stability of mistuned bladed disk can be obtained by changing the structural parameters. For the STCF 4 example, the response calculated by this method agrees well with the results obtained by the direct CFD, but the computational efficiency is improved by nearly two orders of magnitude. This method is used to study the stiffness mistuned cascade system, and the stability characteristics of the system are obtained by calculating the eigenvalues of the aeroelastic matrix. The results show that the stiffness mistuning can significantly improve the flutter stability of the system, and also lead to the localization of the mode. The mistuning mode, mistuning amplitude and fluid structure interaction can influence the flutter stability obviously.

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43

Thermann, Hans, and Reinhard Niehuis. "Unsteady Navier-Stokes Simulation of a Transonic Flutter Cascade Near-Stall Conditions Applying Algebraic Transition Models." Journal of Turbomachinery 128, no. 3 (February 1, 2005): 474–83. http://dx.doi.org/10.1115/1.2183313.

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Due to the trend in the design of modern aeroengines to reduce weight and to realize high pressure ratios, fan and first-stage compressor blades are highly susceptible to flutter. At operating points with transonic flow velocities and high incidences, stall flutter might occur involving strong shock-boundary layer interactions, flow separation, and oscillating shocks. In this paper, results of unsteady Navier-Stokes flow calculations around an oscillating blade in a linear transonic compressor cascade at different operating points including near-stall conditions are presented. The nonlinear unsteady Reynolds-averaged Navier-Stokes equations are solved time accurately using implicit time integration. Different low-Reynolds-number turbulence models are used for closure. Furthermore, empirical algebraic transition models are applied to enhance the accuracy of prediction. Computations are performed two dimensionally as well as three dimensionally. It is shown that, for the steady calculations, the prediction of the boundary layer development and the blade loading can be substantially improved compared with fully turbulent computations when algebraic transition models are applied. Furthermore, it is shown that the prediction of the aerodynamic damping in the case of oscillating blades at near-stall conditions can be dependent on the applied transition models.

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44

Hai, Sun, Yang Lin, and Li Hongxin. "Sensitive Flutter Parameters Analysis with Respect to Flutter-free Design of Compressor Blade." Procedia Engineering 99 (2015): 39–45. http://dx.doi.org/10.1016/j.proeng.2014.12.505.

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45

Hai, Sun, Yang Lin, and Li Hongxin. "Sensitive Flutter Parameters Analysis with Respect to Flutter-free Design of Compressor Blade." Procedia Engineering 99 (2015): 1597–603. http://dx.doi.org/10.1016/j.proeng.2014.12.712.

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46

Sun, Xiaofeng, Xiaodong Jing, and Hongwu Zhao. "Control of Blade Flutter by Smart-Casing Treatment." Journal of Propulsion and Power 17, no. 2 (March 2001): 248–55. http://dx.doi.org/10.2514/2.5770.

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47

Zhang, Yangjun, Naixiang Chen, Deping Tao, and Sheng Zhou. "The effects of unsteady interactions on blade flutter." Chinese Science Bulletin 42, no. 11 (June 1997): 960–62. http://dx.doi.org/10.1007/bf02882558.

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48

Procházka, Pavel, Václav Uruba, Luděk Pešek, and VÍtězslav Bula. "On the effect of moving blade grid on the flow field characteristics." EPJ Web of Conferences 180 (2018): 02086. http://dx.doi.org/10.1051/epjconf/201818002086.

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The motivation of this paper is the continual development of the blades for the last stage of the steam turbine. The biggest problem is the slenderness of such blades and the extreme sensitivity to aeroelastic vibrations (flutter) caused by the instabilities present in the flow. This experimental research is dealing with the aeroelastic binding of the moving blades located in the blade grid with the flow field and vice versa. A parallelogram is used to ensure one order of freedom of the blade. The grid has five blades in total, three of them are driven by force control using three shakers. The deviation as well as force response is measured by strain gauges and dynamometers. The flow field statistical as well as dynamical characteristics are measured by optical method Particle Image Velocimetry. The grid is connected to the blow-down wind tunnel with velocity range up to 40 m/s. The aeroelastic binding is investigated in dependency on used actuation frequency and maximal amplitude (the intensity of force actuation) and on different Reynolds numbers. The flow field and the wake behind each individual blade are studied and the maximal interaction is examined for individual inter-blade phase angle of the grid.

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49

Zhu, Youfeng, Hongyu Zang, Xiaofei Kong, and Peng Ban. "Two-Degree Vibration Analysis of a Horizontal Axis Turbine Blade by Finite Differential Methods." Shock and Vibration 2018 (2018): 1–15. http://dx.doi.org/10.1155/2018/6087295.

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Two-degree vibration partial differential equations of large horizontal axis turbine blades were established by Kallesøe’s model and Greenberg unsteady aerodynamic theory. By means of the finite difference discretization and cantilever beam boundary condition, the equations of blades can be simplified as a general vibration system. Then a linear stationary state space on the system was built. The blade tip vibration in autonomous and nonautonomous system can be simulated by MATLAB vibration toolboxes in time domain. The convergent, flutter, and divergent vibration curves were plotted in the directions of lead-lag and flapping.

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50

Yang, Weichao, Yanrong Wang, Xianghua Jiang, and Xiaobo Zhang. "Flutter analysis of a one-and-a-half-stage fan at low speed using nonlinear harmonic method." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 234, no. 8 (February 10, 2020): 1380–94. http://dx.doi.org/10.1177/0954410020904862.

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Multirow effects on flutter stability of a 1.5-stage fan at low speed are investigated using nonlinear harmonic method in a one-way coupled fashion. In the first part, the mesh-independence verification and validation of nonlinear harmonic method to simulate multirow effects are performed. In the second part, multirow effects are separated into two parts including acoustic reflection and rotor–stator interaction induced by relative motion between rotor and stators with each part investigated individually. Effect of acoustic reflection from upstream and downstream blade rows is investigated separately using a harmonic truncation method to avoid the change of time-mean flow. The results show that acoustic reflection can have a large effect on flutter stability of rotor blade. The simulation of the rotor–stator interaction effect indicates that the rotor–stator interaction does not significantly affect the flutter stability of rotor blade in this case. Lastly, the variation of aerodynamic modal damping ratio with the size of gap between inlet guide vane and rotor is investigated. Aerodynamic modal damping ratio at a nodal diameter whose fundamental mode is cut-on varies periodically with gap size. Wave splitting method is employed to further investigate the relation between the phase difference between incoming and outgoing wave and aero damping, which can be used to improve the flutter stability at the design stage.

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Journal articles on the topic 'Blade flutter'

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